cytology C.pdf

Cytology Course (201 Zoo) For undergraduate students of Zoology- Zoology Chemistry - Biochemistry - Chemistry Preparation Prof. Dr. Abd-Elbasset M. Ebied Aly Professor of Cytogenetics Faculty of Science - Department of Zoology Academic year 2022 / 2023...

Cytology Course (201 Zoo) For undergraduate students of Zoology- Zoology Chemistry - Biochemistry - Chemistry Preparation Prof. Dr. Abd-Elbasset M. Ebied Aly Professor of Cytogenetics Faculty of Science - Department of Zoology Academic year 2022 / 2023 -1-  ‫رؤية الكلية‬ ‫التميز فى تعليم العلوم األساسية والبحث العلمى للمساهمة في بناء اقتصاد الوطن‬ ‫رسالة الكلية‬ ‫تقديم تعليم متميز فى مجاالت العلوم األساسية وإنتاج بحوث علمية تطبيقية تدعم‬ ‫اقتصاد الوطن من خالل إعداد خريجين متميزين طبقا للمعايير األكاديمية القومية‬ ‫وتطوير مهارات وقدرات الموارد البشرية وتوفير خدمات مجتمعية وبيئية تلبى‬ ‫طموحات مجتمع جنوب الوادى وبناء الشراكات المجتمعية‬ ‫رؤية القسم‬ ‫خريجون وباحثون متميزون علميا وبحثيا محليا ودوليا خدمة للمجتمع وتنمية للبيئة‬ ‫رسالة القسم‬ ‫يسعى قسم علم الحيوان بكلية العلوم من خالل ما يقدمه من برامج تعليمية متطورة‬ ‫وبحث علمى تطبيقى وبنية أساسية مناسبة إلى خريجين متميزين محليا ودوليا فى‬ ‫مجاالت العلوم البيولوجية ينتفع بهم المجتمع وسوق العمل‬ ‫‪Book data‬‬ ‫‪College: Science‬‬ ‫‪The second band‬‬ ‫‪Specialization: Zoology Chemistry - Biochemistry - Chemistry‬‬ ‫‪Publication date: 2022 / 2023‬‬ ‫‪Number of pages‬‬ ‫‪Authors: Prof. Dr. Abd-Elbasset M. Ebied Aly‬‬ ‫‪-2-‬‬ The aims of the course study 1-Giving the student abundant information about a real cell, studying living cells; its properties, structure and components, the organelles present in it, its interaction with the environment, its life cycle, division and death. 2-Introduce the student to the chemical and molecular composition of the cell. 3-Introducing the student to the different components of cells in general, with a focus on knowing some groups about each other or with each other, provided that they are related to each other. 4- Introducing the student to the genetic content of the organism and the role of the cell in the inheritance of hereditary traits. -3-  ‫بسم هللا الرحمن الرحيم‬ ‫الحمـد هلل و الصالة و السالم على رسول هللا و على آله وصحبة و سلم تسليما كثيرا‬ ‫وبعـــــــــــــد‪,,,,,‬‬ ‫جميل جدا أن يرتبط االيمان بعلم له عمقه ومغزاه ‪....‬خاصة اذا كان هذا العلم فى‬ ‫آيات هللا ‪....‬فعالم الدين الورع تسعده آيات القرآن الكريم سعادة ال تدانيها سعادة أخرى‬ ‫‪.....‬خاصة اذا تأمل فى معانيها و تذوق جمالها و كذلك يكون رجل العلم التجريبى‬ ‫المتأمل فى آيات الخلق الكثيرة التى تنظم تواجد مخلوقات هللا كما يشاء المولى عز و‬ ‫جل و التى تمتد حوله بال حدود‪.‬اذ يسعد و يخشع لنظمها المتقنة و دقتها المتناهية‪.‬‬ ‫لذا فما أجمــل ما عبــر القـــرآن الكريم أروع تعبيــــر (و فى األرض آيات للموقنين‬ ‫و فى أنفسكم أفال تبصرون)‪.‬لذا فاآليات القرآنية كثيرة اإلشارة إلى الحض على التأمل‬ ‫فى اآليات الكونية و البحث فى النواميس الطبيعية‪ ,‬ألن مغزى ذلك ال يخفى على لبيب‬ ‫‪ ,‬اذ بقدر ما نكتشف من بديع صنع هللا بقدر ما تتجلى لنا عظمته و دقته ‪ ,‬خلق فسوى‬ ‫و قدر فأبدع ( الذى خلق فسوى و الذى قدر فهدى )‪ ,‬و عندئذ نتقرب اليه أكثر و أكثر‬ ‫و نعبده عبادة قائمة على علم و هدى خير و أبقى من عبـــادة ال تساندها معرفة حقــــه‬ ‫باهلل سبحانه فى قدره و شأنه‪.‬‬ ‫االنسان بال شك خلق عظيم‪ ,‬ولكن ذلك ال يتجلى لنا اال بالبحث فى أصول هذا‬ ‫الخلق والتطلع الى تكويناته المذهلة التي أعيت العقول‪.‬وال شك أننا كلما تعمقنا في‬ ‫دراسة الجسم البشرى كلما أدركنا المعنى العظيم الذي تنطوي عليه بعض اآليات‬ ‫القرآنية والتي أشارت الى ضرورة التأمل في أنفسنا و فى كل شئ حولنا‪ ,‬فهذا يوضح‬ ‫لنا ما خفى علينا من أسرار و ما أكثر ما يخفى علينا من أسرار‪.‬فهل ندرك بحق كيف‬ ‫تعمل هذه األعضاء (السمع والحس‪ ,‬االبصار والفؤاد) فلو عرفنا ذلك حق المعرفة‬ ‫الستقر االيمان بقلب المسلم‪.‬ايمانا باهلل تعالى منزل القرآن ومرسل الرسل ومجازى‬ ‫الناس على اعمالهم كال بما كسبت جوارحه‪.‬‬ ‫وهللا أسأل أن يتقبل هذا العمل والجهد فانه جهد المقل‪.‬وأسأله أن ينفع به‬ ‫ويجعله خالصا لوجهه الكريم‪.‬و يجعله ذخرا لي عند انقطاع عملي و انتهاء أجلى و‬ ‫انه أهل التقوى و أهل‬ ‫يتجاوز به عن ذلتي و يمحو به خطيئتي‪,‬‬ ‫المعرفة‪.‬‬ ‫أ‪.‬د ‪ /‬عبد الباسط مسعود عبيــد‬ ‫‪-4-‬‬ The cell -5-  Introduction What kind of science is this that we are talking about, that it is the science of creation, a science that begins with Him and with which life, survival, existence for any being? It is the science of the beginning and the end of creatures, the science of the cell. Cell biology is defined as the science that deals in detail with the study of the cell and its contents and what goes on inside it of the various vital processes. In other words, it is the science that deals with Structural and functional system of protoplasm and its relationship to various vital activities including growth of cells and development, genetics and other different processes. Therefore, cell science is one of the branches of biological sciences that specializes in studying the composition, chemistry and functions of cells. The cell is the unit structure and functional unit of a living organism. It is made up of structural units that are cells. After the invention of the light microscope, scientists were able to see tiny units that could not be seen with the naked eye, and they called them cells. Cells are considered to be the essential units of living organisms. Therefore, the discovery of the cell is a very important matter and has a great impact, because we are living in these days the revolution of technological progress, biotechnology, which is the accurate analytical period of science, and therefore it has become almost certain to identify the vital activities and the various processes that occur within this delicate entity that is not seen with the naked eye. Here the hand of divine power is manifested in this delicate structure, so that every intelligent person can contemplate who created this entity and commanded it to work non-stop, without maintenance, without spare parts. And after identifying the accurate analysis of the cell, its main elements are separated so that scientists can identify the different forms of energy that exist inside the cell, which are called manifestations of cell life. -6- History of cytology The world is how strange it is in everything. Recently, our knowledge of animal and plant organisms did not go beyond the apparent or morphological description of the animal or plant, which is seen with the naked eye, but after the discovery of the light microscope, as we talked about before, it was possible to learn a lot about minutes. The structure of these organisms. In the year (1665-1668) Robert Hooke found, while examining a thin section of cork plant under a light microscope, that it was composed of small hollow chambers, which he called cells because they resemble honey bee cells, Therefore, Robert Hooke became the first scientist to use the term cell and defined it as a chamber, void, or cavity surrounded by a wall from the outside, but he did not mention whether this void contains other structures or not. Scientists raced to identify the contents of the cell. In the year 1700, Leiuwin Hooke discovered the nucleus inside the cell, and thus the definition of the cell became as a cavity or a void containing a nucleus and surrounded by a wall from the outside, by watching red blood cells in salmon..... And the scientist Robert Brown (1831) confirmed the presence of the nucleus inside every animal cell. In 1835, the scientist Dejardin described the contents of microorganisms as a jelly-like substance, elastic, contracted, clear, homologous, and insoluble in water, and he named this substance that possesses such characteristics as sarcod. While in 1838, Schleidin, a botanist, explained that cells are the structural and structural units of plants.. Thus, Schleidin is the first scientist to introduce the term cell to plant organisms, and therefore plant tissues are nothing but aggregations of cells. And so the cell became the structural unit of the plant, and also after one year, in 1839, the German zoologist Schwann reached the same conclusion for the animal, and the animal tissues became nothing but clusters of the cells and that the cell is the structural unit of the animal, and Schwann was the first to use the concept of cell theory, which is that “cells are living organisms, and that plants and animals are nothing but aggregations of these organisms arranged according to special laws, and this means that all Living organisms are animals or plants whose bodies are composed of cells, and there is another -7- group of scientists who have reached the same conclusion in a less or more likely way. In 1840 Perkeinje called the contents of the animal cell protoplasm, and six years later (1846) von Vonn endorsed Perkeinje's opinion and used the concept of protoplasm on the contents of the plant cell. While the scientist Max Schultz (1861), who is German, explained the similarities and differences between sarcoid and protoplasm. Also, scientists have verified that protoplasm is the basic component of cells in both animals and plants. And that the cell wall, in addition to being dead, is only found in the plant cell and is not found in the animal cell Accordingly, the cell was defined as a mass of protoplasm containing a nucleus and surrounded by a membrane from the outside, but this definition lacks accuracy for the following reasons; Some cells contain two nuclei rather than one nucleus, others contain more than two nuclei, and in contrast some other cells such as mature red blood corpuscles do not contain a nucleus. Some of this followed another group of scientists in search of a new discovery that serves humanity for the concept of the cell that represents the nerve of animals and plants.... In the year (1841) Rimac discovered direct cell division, amitosis, while Schneider in the same year was able to discover mitosis For the first time in the year (1854), the scientist Newport was able to see the entry of the sperm into the ovum of the frog animal, while Hertwig (1875) explained the fusion of the sperm with the egg, and with this characteristic, scientists were able to understand the laws of genetics. Thus, the organic organization of the cell is recognized. We all know that this era is the era of successive scientific shouts, which man will not be able to follow. One of the factors for the emergence of such rapid scientific progress is the emergence of its own technical tools (electron microscope), which changed a lot of our previous knowledge about some scientific concepts, especially the cell, hence, we had to study the cell from two different perspectives in order to properly identify the cell. The first perspective is the living cell, and the second perspective is the fixative cell. This is only possible in the presence of microscopes. -8- Microscopes Due to the small sizes of the majority of cells, which cannot be seen with the naked eye, and the contents of these cells have a close refractive index, which makes it very difficult to identify the cells and their contents, except in the presence of tools that help in knowing the composition and contents of these cells, and among these tools are microscopes, which were invented by the scientist Leeuwenhoek (1591-1623). There are different types of them according to the type of use, including simple and compound light microscope, contrast microscope, fluorescent microscope, field microscope, electron microscope and other types. What meaning the cell? A cell is a living organism that cannot be seen with the naked eye. It consists of three basic components, groups of protoplasm, with one or more nuclei inside, or without, and surrounded by a membrane or a wall from the outside. It is the basic unit from which the bodies of all living organisms are composed, and it is small in size, the largest of which does not exceed 100 micrometers in size, and it is of two types: eukaryotic cells, which are cells whose nuclei are surrounded by a membrane, and examples of them are the cells that make up the bodies of each of the protests, fungi, and plants, And animals, but prokaryotic cells do not contain a nucleus surrounded by a membrane, Examples include bacteria and archaea. Components of an animal cell Animal cells are the cells from which the bodies of animals are composed. Animal cells contain organelles common to plant cells, such as the cell membrane, cytoplasm, nucleus, mitochondria, endoplasmic reticulum, Golgi bodies, ribosomes, and others. They also contain special organelles that are not found in plant cells, such as the centrosome, lysosomes, and cilia. , and flagella. Cell types The cells are of three types in terms of the nucleus: prokaryotic (bacterial cell) and eukaryotic cell (animal and plant cell), somatic cell, sexual cell, and also the cell that makes up the organ, and all of this shows the concept of cellular organization. -9- Cellular organization The cell is the structural and functional unit of living organisms, and there is no typical cell because cells differ in shape, size, and function. So, there must be three main characteristics in the cell in order for it to live a free, independent life without relying on others: the presence of the plasma membrane, the presence of the enzyme system for energy production necessary for construction processes, and the ability to reproduce. After that, cell science developed, and a modern classification of living organisms was developed, based on me. Cellular organization, in which all organisms except viruses were included in two groups 1-Organisms with prokaryotic cells 2-Organisms with eukaryotic cells Viruses are left out of this division and do not belong to any of the six known kingdoms as self-contained units. Comparison of prokaryotic and eukaryotic cells eukaryotic cells Prokaryotic cells Adjective Mostly large (10-100 microns) Mostly small (1-10 microns) cell size DNA is associated with histone DNA with some histone proteins Genotype and non-histone proteins Mitosis and meiosis Direct binary division or budding cell division They are distributed in the There are no..... except for some cytoplasmic cytoplasm and the ribosomes are ribosomes organelles larger in size It occurs as a result of complete If any, it is by transferring genes sexual system fusion of the nuclei in one direction flagella or complex cilia Simple flagella in some bacterial movement species members - 11 -  Absorption, ingestion and Most of them are absorbed, and nutrition photosynthesis relate to each some are photosynthesized other Mitochondria are present Mitochondria are not present Metabolic energy Bacteria 1- They are the largest of the prokaryotic families 2- Bacteria belong to the Monera kingdom 3- Bacteria can be divided according to their forms or according to the type of their nutrition, or according to their movement.... etc 4- All types of bacteria reproduce asexually, although sexual reproduction has been observed in some types 5-The bacterial cell consists of the following a-The nuclear material (the bacterial ring chromosome) that contains the genetic information b-Plasma juice (cytosol) and contains ribosomes and organic matter c- Cell wall: It gives the cell its well-known shape, and it is thin but solid and semi-permeable d- Plasma membrane: It is a semi-permeable membrane that contains respiration enzymes e- Capsule: It is found in some bacteria but not in others. It covers the cell wall from the outside f-Flagella: Some bacteria do not have flagella and are used for locomotion g-Cilia: are minute extensions located around the cell. - 11 - Eukaryotic Cell The eukaryotic cell consists of a mass of protoplasm that contains one or more nuclei or not and is surrounded by a membrane from the outside (animal cell) or a wall from the outside (plant cell). Fig (1): The animal cell Protoplasm Protoplasm is the living substance of which all living animal and plant organisms are composed. Without protoplasm, there is no life at any level. Therefore, Huxley said in the year (1868) the famous saying that “protoplasm is the natural basis of life.” This means that all vital activities that are carried out the living organism is caused by the chemical and natural changes that occur in the natural basis of life (protoplasm). The term protoplasm is applied to various materials of which the cytoplasm and the nucleus are composed, and some others. The term protoplasm is used for the different materials that make up the cytoplasm only. The protoplasm of one type of cell differs from another type, and it is characteristic of the cells of organs and species. It should be noted that the improvement in modern technology, examination and clarification of cellular structures and the use of vital dyes - 12 - have had a great advantage in opening up new and wide horizons in cell researches. It is noted that there are many anatomical forms in relation to the animal cell, because there are many forms of the animal cell, including these forms as well. Chemical composition of protoplasm It is not possible to identify the exact chemical composition of protoplasm, fine chemical composition of protoplasm, as it is not possible to analyze the protoplasm without killing it by chemicals, and therefore chemical changes occur that result in new substances or the disappearance of substances from the basic components of the protoplasm. Also, the protoplasm during the normal activity of the cell secretions secretions Thus, his analysis is not an accurate analysis. In addition to that, as we talked about before the protoplasm It differs from one cell to another, for example, the protoplasm of the hepatic cell differs from the protoplasm of the nerve cell, and so on. Potassium, sulfur, sodium, magnesium, phosphorus, and other elements) and it also contains carbon, hydrogen, oxygen, and nitrogen in different proportions. The elements together form two types of organic compounds (proteins - fats or lipids - carbohydrates - nucleic acids) and inorganic components (water and mineral salts). Organic components of the cell Organic compounds, mean compounds that must contain both hydrogen H and carbon C together with the presence of any other elements. The animal cell contains four types of organic compounds:- Proteins Protein materials are the most common and widespread organic materials in animal protoplasm and among the distinctive forms of living matter are protein materials and protein materials include the following components: - Carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) in addition to other elements that are found in small proportions Such as sulfur (S), phosphorus (PH), calcium (Ca), and other elements. Protein molecules are complex in structure, and their simplest structural units are amino acids. A real visualization of the structure of protoplasm and these simple units of proteins are nothing but organic acids that contain amino acids that form a long chain of them in union with each other. - 13 - Proteins - proteoses - peptones - polypeptides - dipeptides - amino acids. These amino acids pass into the blood circulation, which carries them to the cells that convert them into animal proteins similar to body proteins, under the influence of special cellular enzymes. Hence, we find that each cell has a set of free proteins, from which the cell chooses what it needs to build for itself of necessary proteins, and these proteins are called the "cell pool". Types of proteins Proteins are classified on the basis of the nature of the decomposition products of these protein substances into three types:- simple proteins The decomposition of this type of protein gives amino acids only, and among these examples are the following. A- Histones: - one of the most important features that distinguishes them is that they dissolve in water, but do not dissolve in diluted ammonia. This protein is the main component of chromosomes. Organisms differ according to the difference in their contents of proteins. B - Albumines: - Proteins that dissolve in water and also coagulate if exposed to heat C - Golobulins: This type of protein is soluble in acids, alkalis and salt solutions, but it does not dissolve in water. D - Protamines: - dissolve in water, but do not coagulate when heated Associated proteins It contains the types in which simple proteins can be combined with other substances, and it contains the following types: A- Glycoproteins: In which proteins are bound together with carbohydrates B - Nucleoproteins: - They result from the union of a protein with nucleic acid. C- Lipoproteins, which result from the union of protein with fat. - 14 - Derived proteins They are complex proteins that have undergone partial degradation, such as the decomposition of proteins into proteases, and proteoses into peptones, and so on. Sources of proteins There are two sources of proteins, one of which is animal, which is meat of all kinds, fish, birds, and eggs, while the second source is vegetarian, such as various types of legumes; Beans - lentils - peas - beans - cowpeas and others. The functions of proteins Proteins play an important and vital role for the organism, as 1-It is used as a real source of growth by adding it to the structure of the body. 2-It works to replace damaged protein fibers in the body 3- Contribute to the synthesis of hormones. 4-It has the ability to unite with other elements and substances to form important compounds for the body, such as its union with iron to form hemoglobin and others. Carbohydrates They are compounds consisting of oxygen, hydrogen, and carbon. The first two elements are found in the same proportion as they are in water. These substances are found in a complex form, such as animal starch (glycogen), vegetable starch, cellulose, and other simple ones such as monosaccharide's. Types of carbohydrates Carbohydrates can be divided into three types: Monosaccharide's, disaccharides, and polysaccharides. Monosaccharide's and disaccharides are known as sugars due to their sweet taste. Therefore, they also have the - 15 - ability to spread through saturated membranes. They also have solubility in water. As for the polysaccharides, they do not spread through the saturated membranes and do not crystallize and form colloidal solutions with water. Monosaccharide's are simple sugars, and the most important of these compounds in the animal cell are pentose and hexose sugars, and they are found united with proteins and fats. Ribonucleic acid and Deoxyribonucleic acid), while the hexose sugars are responsible for providing the vital energy needed for the body. Disaccharides consist of the union of two parts of monosaccharide's with the loss of a part of water and the most important of these types is milk sugar (lactose) and consists of two parts of glucose and galactose; Maltose consists of two parts of glucose, while cane sugar (sucrose) consists of two parts, glucose and fructose. Polysaccharides are consists of the union of several molecules of monosaccharide's with the loss of molecules of water. One of the most important polysaccharides is vegetable starch (which represents the reduced carbohydrate substances in plant cells and is formed from carbon dioxide and water in the presence of chlorophyll) and vegetable cellulose (which is the main component of the plant cell wall and also participates in the formation of the structures responsible for the formation of the structural support of the plant) and animal starch, which represents the reduced carbohydrates in animal cells, which It is of great importance to the animal, and despite its presence in many body tissues, the largest part of it is found in the liver, which represents 3% of the weight of the liver, and the muscles. It is known as glycogen, and glycogen is somewhat soluble in water and is likely to dissolve. In the protoplasm, it can be indicated in the liver cells through a certain type of dyes, as it gives a red color with the best carmine dye. Nucleic acids Nucleic acids are very important chemical compounds, they are very important chemical compounds, and they are found in all living organisms, and the organism contains at least one acid, so some viruses contain - 16 - ribonucleic acid, such as the Poliomyelitis Virus, or some of them contain It contains only deoxyribonucleic acid, such as bacteria, but higher plants and animals contain both ribonucleic acid and deoxyribonucleic acid, and deoxyribonucleic acid occur in the nucleus and mitochondria only, and most of the chromosomal composition (from 90% - 95%) is when the cell is in a state of division while the cell is in the resting period or the interphase stage, and there is Deoxyribonucleic acid in the chromatin threads and In the nucleus, Deoxyribonucleic acid combines with proteins (peptones and protamine's) to form nucleoprotein. As for ribonucleic acid, it is found in different regions. Some other materials are specific compounds such as amino acids and proteins, and these materials are of particular importance in the formation of nucleic acids. The nucleic acids represent the identity card for every living organism through which the genes responsible for showing the hereditary characteristics (physical and sexual) of each organism are carried. Components of nucleic acids The simplest units of nucleic acids are nucleotides, which consist of three molecules: a five-sugar molecule (ribose or deoxyribose), a phosphoric acid molecule, and a base nitrogen molecule (pyrimidine bases or purine bases). The pentose sugar and basic nitrogen's are known as nucleosides, and the pyrimidine nitrogenous bases are cytosine, thymine, and uracil, while the purine nitrogenous bases consist of adenine and guanine, and both DNA and RNA contain adenine, guanine, and guanine. In addition to cytosine, DNA contains thymine, while RNA contains uracil. Fatty materials They are substances that represent another source of energy, and therefore consist of the same elements that make up carbohydrates, namely: Hydrogen, oxygen, carbon, and other elements. The protoplasm contains true fats and their derivatives and substances. Fatty insoluble in water, but soluble in organic solvents such as petrol and some other solvents. The importance of fat Fats play a vital and important role within the tissues of the body, and this role depends on their location and the image on them. For example, - 17 - glycerides act as a source of thermal energy and a safety bulwark against cold and help resist any harm to the body, while phospholipids are found within the nervous tissue. And it is responsible for the formation of the myelin substance, through which the nerve fibers know whether they are myelinated or not. Regulating the mechanical functioning of the skin and hair, such as cholesterol. There are two types of fats in the tissues of the body: neutral fats and phospholipids, and the second represents the true fat of the protoplasm and true fats are not affected by various factors. For example, the fats that are found in brain tissues are real fats, and therefore during the fasting period they are not affected, and we also find that the liver represents the main axis of fats inside the body. Importance in the process of fat metabolism. The liver naturally contains 4% lipids (1:3 fats Essential and phospholipids) and the rate of fat in the liver increases during the first period of the fasting process, because the fatty substances move from the body stores to the liver to oxidize them, and then the fat in the liver begins to gradually decrease. Second - inorganic components Protoplasm contains inorganic components in the form of salts united with organic components, as they combine with protein materials (amino acids) forming some hormones (thyroxin) or some other compounds (hemoglobin & haemocyanine) and the concentration varies these elements are inside the cell rather than outside it. Mineral salts They are inorganic salts that are found dissolved in protoplasm and bodily fluids, constituting approximately 1% of body weight. Examples of these are potassium chloride, sodium chloride, calcium phosphate, carbonate, and other salts. Mineral salts play an important and vital role. For example, if the amount of calcium decreases from its normal rate in the blood, it may lead to death. Also, in the case of a deficiency of sodium and potassium from their usual percentage in the body, the heart and muscles cannot perform their functions in a natural way. This is in addition to the - 18 - importance that the public knows. It is accepted by specialists that the teeth and bones consist mainly of salts. water The Lord Almighty says in his holy book, “In the name of God, the Most Compassionate, the Most Merciful, and We made from water every living thing. Water almost 000, for example but not limited to, water is used as a solvent for many different compounds, as it is the medium that is essential for the occurrence of most, if not all, of the bodily physiological processes such as digestion, respiration, excretion, absorption, excretion, and other various processes 000, along with This works to protect the body from sudden changes in temperature. The amount of water varies from one tissue to another, as the human bone tissue contains approximately 10%, while the muscle tissue contains approximately 75%. Even in one organ, the amount of water varies from tissue to tissue. For example, the white matter tissue in the brain contains 68 % While the tissue of the gray matter of the brain contains approximately 84% of water 000 Also, the amount of water for the same tissue varies according to the age of the tissue, as the tissue in the embryonic stages contains a higher percentage of water than in the aging stage, to 90% of the brain weight, while it reaches 75% of the brain weight of the adult mouse 00 and therefore the percentage of water inside the tissue is related to the functional performance of the tissue. Cytoplasm Cytoplasm is a viscous (gel-like) substance surrounded by the cell membrane. It consists of cytosol as well as inclusions and a number of cellular organelles with different functions. Components of the cytoplasm A- Cytoplasm: A sticky substance that contains water, proteins, carbohydrates, enzymes and inorganic salts. - 19 - b- Cytoplasmic organelles: living structures that float in the cytoplasm and perform certain functions that serve the life of the cell. It is divided into membranous organelles and non-membranous organelles. C- Cytoplasmic Inclusions: Non-living substances stored in the cytoplasm. It includes storage nutrients such as glycogen, fats, and pigments such as hemoglobin, melanin, etc. It also includes some crystals. Function 1-If the cell is devoid of cytoplasm, it will not be able to maintain its shape, it will be hollow and flat, and the organelles will not remain suspended in the cell solution without the support of the cytoplasm. 2-Most of the enzymatic reactions and metabolic activity of the cell occur in the cytoplasm. 3-The cytoplasm helps move substances, such as hormones, around the cell and also dissolves cellular waste. Second: the living components of the cell protoplasm The cell protoplasm includes many living components, including:- The plasma membrane The scientist Daniele (1952) dealt with the structure of the cell membrane in the form of a model known as Daniele's model of the cell membrane, in which he shows that the cell membrane consists of three layers and not one layer, the outer and inner layer is protein, while the middle layer is lipids (fats). In the form of two parts, but this structure did not explain how substances that are not soluble in fats enter the cell, Then Danielle (1954) developed his idea, explaining that the cell membrane is a non-contiguous structure and that it contains bores through which substances that do not have fat solubility pass into the cell. Danielle (1954) stated that the cell membrane is a three-layered structure, but he added that the double layer of lipids has a hydrophilic outer part while its inner part is hydrophobic, and that the cell membrane is surrounded from the outside by a thin surface layer of mucous sugary substances called the goblet envelope or sugar coat. The plasma membrane consists of both lipids and proteins. The fundamental structure of the membrane is the phospholipid bilayer, which - 21 - forms a stable barrier between two aqueous compartments. Proteins embedded within the phospholipid bilayer carry out the specific functions of the plasma membrane, including selective transport of molecules and cell-cell recognition. Lipids The cell membrane consists of three classes of lipids: phospholipids, glycolipids, and cholesterols. The amount of each depends upon the type of cell, but in the majority of cases phospholipids are the most abundant. Cholesterol molecules scatter between phospholipids, thus maintaining the plasticity of the plasma membrane, and preventing the cell membrane from being filled with phospholipids. Cholesterol is found only in animal cell membranes, and it is not found in plant cell membranes. Glycolipids are found on the outer surface of the plasma membrane, and they have a role in distinguishing cells from other cells that make up the body. Fatty acids may be saturated or unsaturated. Plasma membrane lipids are arranged in two layers, and are facultative permeable; That is, it allows certain molecules to pass through it and not others, depending on the cell's need for them. Among the types of fats in the plasma membrane are phospholipids, which are an essential part of the - 21 - bilayer plasma membrane lipids, and they consist of two parts; Hydrophilic heads, and therefore are arranged so that they face the cytosol (the watery part of the cytoplasm), the fluids that exist outside the cell, and hydrophobic tails; Therefore, there are two layers of water-loving heads; This is so that it is far from the cytosol and the fluids that exist outside the cell. 2-Proteins Proteins are the second major component of plasma membranes. There are two main categories of membrane proteins: integral and peripheral. In addition to lipids, membranes are loaded with proteins. In fact, proteins account for roughly half the mass of most cellular membranes. Many of these proteins are embedded into the membrane and stick out on both sides; these are called transmembrane proteins. The portions of these proteins that are nestled amid the hydrocarbon tails have hydrophobic surface characteristics, and the parts that stick out are hydrophilic. At physiological temperatures, cell membranes are fluid; at low temperatures, they become gel-like. Scientists who model membrane structure and dynamics describe the membrane as a fluid mosaic in which transmembrane proteins can move laterally in the lipid bilayer. Therefore, the collection of lipids and proteins that make up a cellular membrane relies on natural biophysical properties to form and function. a- Peripheral membrane proteins Peripheral membrane proteins are proteins that are not directly related to cellular communication, but rather related to other proteins that are found in the membrane. The second type of proteins are the fused membrane proteins. Proteins contained in the embedded proteins, in the membrane. Peripheral membrane proteins, which are proteins that are not directly associated with the cell membrane, but rather are associated with other proteins that are found in the membrane. b- Integrated membrane proteins The second type of proteins are the integrated membrane proteins. Integral membrane proteins are embedded in the plasma membrane, and their tips - 22 - extend to appear on either side of the membrane. Types of protein in cell membrane. Proteins can be divided according to the function they perform into the following types 1-Structural proteins have several properties, most notably the following: Building structural proteins begins immediately after DNA replication. Structural proteins are divided into three major types, and eight minor ones. Structural proteins provide support for bone, cartilage, hair and muscle Structural proteins include collagen, actin, and keratin proteins. 2- Receptor proteins are a special category of proteins that support the life of the cell, and work by providing special places on them (receptors) that are ready to bind to various molecules, as this receptor, when associated with a specific molecule, can change its shape and send a signal that carries a specific meaning to the cell to cause specific response. Receptor proteins are characterized by staying most of the time on the surface of the cell, and in some other cases moving around, performing a series of complex functions. 3- Transport proteins are a type of proteins found in the cell membrane, which facilitate the process of transport and diffusion of materials, and one of its most prominent characteristics is the transportation of materials from inside to outside the cell through the plasma membrane. They are found in cell membranes, mitochondria, and chloroplasts. Glycoproteins are molecules composed of both proteins and carbohydrates. It is characterized by the following: Glycoproteins are involved in many physiological functions; as the secretion of globin, which is necessary for the immune system. Glycoproteins help the body produce collagen and myosin, which are proteins secreted in the digestive and respiratory systems. Glycoproteins in red blood cells determine your blood type. Interferes with the synthesis of some gonadal hormones, such as; Hormones of growth, puberty, and reproduction. Carbohydrates Carbohydrates are the third major component of plasma membranes. In general, they are found on the outside surface of cells and are bound either to proteins (forming glycoproteins) or to lipids (forming glycolipids) (fig. 5). These carbohydrate chains may consist of 2-60 monosaccharide units and can be either straight or branched. Along with membrane proteins, - 23 - these carbohydrates form distinctive cellular markers, sort of like molecular ID badges, that allow cells to recognize each other. These markers are very important in the immune system, allowing immune cells to differentiate between body cells, which they shouldn’t attack, and foreign cells or tissues, which they should. Chemical structure of the cell membrane As we talked about before through Danieli’s model of the cell, the cell membrane is composed mainly of lipids at a rate of up to 30% and proteins at a rate of up to 70%, and it also contains carbohydrates at a rate ranging from 1% to 5% according to Robertson in 1959. Mobility of Membrane Proteins The principal components of the plasma membrane are lipids (phospholipids and cholesterol), proteins, and carbohydrate groups that are attached to some of the lipids and proteins. Function of plasma membrane One of the important functions of the plasma membrane is the transport of materials to and from the cell, and among the most important methods of transporting materials across the plasma membrane are the following 1-Diffusion: Diffusion is the movement of solutes across the plasma membrane from an area of high concentration to an area of low concentration to reach a state of equilibrium. That is, the presence of equal concentration on both sides of the plasma membrane, without the need for energy, or transport materials, such as: enzymes. 2-Facilitated diffusion the transfer of solutes from an area of high concentration to an area of low concentration with the help of transport proteins, without the need to expend energy. 3-Active transport of substances across the plasma membrane against the direction of concentration; That is, from the region of low concentration to the region of high concentration with the help of transport proteins that act as a pump, and this type of transportation needs energy. 4-Filtration The transport of solutes, solvents, and ions across a membrane; with the help of hydraulic pressure. - 24 - 5-Osmosis is the movement of a solvent from a lower concentration of a salute to a higher concentration. 6-Endocytosis: It is a method for transporting large-sized materials into the cell, and it takes place as follows: the cell membrane folds around the material that the cell needs inside, and a sheath or a small pocket is formed that begins to shorten and deepen to form a vesicle, which then separates from the cell membrane, thus becoming inside the cell, which is a process completely opposite to the method cellular output. 7-Exocytosis The transport of substances out of the cell via secretory vesicles. Cell organelles There are many cellular organelles within the cell which are divided into two types: 1-Membranous organelles: They are surrounded by a membrane and include: endoplasmic reticulum - Golgi apparatus - mitochondria - lysosomes - vacuoles – peroxisomes. 2-Non-membranous organelles: do not contain membranes and include: ribosomes - centrosome - cytoskeleton (microtubules and filaments) - cilia and flagella. Membranous organelles There are many cellular membranous organelles within the cell as Mitochondria Many scientific researches were conducted dealing with the animal cell as well as the plant, starting from the end of the nineteenth century and until this day, advanced research is still being conducted with the development of modern technologies. Benda the world and the presence of mitochondria in all cells in 1897. The cytoplasm of the cell contains mitochondria in the form of living organisms, and they were identified through the light microscope, which showed them in the form of small granules, short rods, vesicles, or fine filaments, and these shapes took different names. It bears the shape of short rods and small threads in chondrioconts, while mitochondria are granular in shape, called chonderiomites, while - 25 - mitochondria in vesicular shape are known as chondriospheres. Mitochondria are the plant generators of energy, power plants in the cells, or divine factories within which the chemical energy present in food is converted into a type of energy that is used by the various cells of the body. Morphology of mitochondria Is it necessary for a cell to contain only one form of mitochondria? Each cell contains one or more distinct forms of mitochondria. For example, pancreatic cells contain the filamentous form of mitochondria, while the genital cells (eggs and sperms Sperms & Eggs) contain the granular form of mitochondria, while nerve cells contain two forms of mitochondria, which are short rods and small threads (Chonderioconts). We also find that the intestinal epithelial cells contain the vesicular, granular and filamentous forms within a single cell, and this means that the cell can have one form or several forms. Size , number and position of mitachondria Animal cells do not contain a single size of mitochondria, but the size of mitochondria varies according to cell activity, but it is noted that the width of mitochondria is almost constant, while its length varies from cell to cell and the user installer. The number of mitochondria varies according to the type, condition and function of the cells. For example, the liver cell of mammals, Mammalian hepatic cells, contains about 2500, while this number decreases and may reach approximately 200 in hepatoma cells. Mitochondria are spread in normal conditions throughout the cytoplasm, but in other cases, it may be concentrated in certain regions. We find that mitochondria in kidney cells are clustered in the basal region of the cell, while in other types of cells the location of mitochondria varies according to their function as an energy source. In retinal cells, mitochondria occupy the inner region of the cell's precise structure, while they occupy the edge of the cytoplasm in neurons. Structure of mitochondria We discuss the exact structure and chemical composition of mitochondria:- - 26 - Ultra structure The use of an electron microscope, through which it appears in the form of a cavity surrounded by a smooth outer membrane, the outer mitochondrial membrane that surrounds and envelops the entire organelle is 60 to 70 angstroms thick. This membrane has a protein-to-phospholipid ratio equal to that of the cell membrane (about 1:1 by weight, i.e. 50% by weight protein and 50% lipid) and contains large numbers of compact membrane proteins called purines, and inside this membrane there is another membrane called inner membrane that extends inside the mitochondrial cavity in the form of a group of crests, separators, or barriers that divide the cavity into a group of small chambers. This membrane contains over 151 different polypeptides and has a high protein-to-phospholipid ratio (more than 3:1 by weight, which is approximately one protein for every 15 phospholipids). The inner membrane is home to one-fifth of all the proteins in mitochondria. In addition, this membrane is rich in phospholipids. We also note that the inner membrane divides the mitochondria into two chambers, an outer chamber located between the outer and inner membranes, and an inner chamber bordered by the inner membrane and filled with a substance known as the interstitial substance of mitochondria. Also, mitochondrial barriers divide the inner chamber incompletely, and the existence of such barriers and their forms is considered a kind of mutation to obtain an ample surface area on which vital processes take place. Therefore, we find that the mitochondria contain very fine granules distributed regularly on the mitochondrial barriers, and these granules represent gatherings of respiratory enzymes and the liver cell contains about 15,000 respiratory enzymes, while in the cells of the bird's muscles, each cell may contain 100,000 respiratory enzymes. The matrix is the space surrounded by the inner membrane, and contains about two-thirds of all the proteins in mitochondria. The matrix is important in the production of ATP. The matrix contains a highly concentrated mixture of hundreds of enzymes, mainly mitochondrial ribosomes, rRNA, and several copies of the mitochondrial DNA genome. - 27 -  Mitochondria Chemical composition The chemical composition of mitochondria differs from one cell to another according to the conditions and the extent to which they are affected by pathological changes. Mitochondria are chemically composed of lipids (about 30%) and proteins (about 70%). Demonstration of mitochondria In order for mitochondria to be identified and explained inside the cell by providing a modern technical means represented by the use of a phase - 28 - contrast microscope, due to the inability to view them with a regular optical microscope, so mitochondria can be seen in the cell either. 1-Live cell, by injecting the cell with a specific dye that affects only the mitochondria, such as the green or black Janus stains. The green Janus stains the mitochondria in a bluish-green color, while this dye does not appear in the other contents of the cytoplasm, and that to reduce it to a base substance. 2-Fixative cell image: - In this case, the cell must be fixed with a suitable fixative (Chromic acid or Osmium tetroxide) so that the components of the cell do not decompose, especially the lipoprotein structure, and after that the cell is dyed with a suitable dye. It only dyes mitochondria without dyeing other components of the cell, such as Altmann acid fuchsin, Regaud's iron-alum haematoxylin, Benda's crystal violet solution, and other dyes. Heterogeneity of mitochondria The different shapes of mitochondria within the different cells and how the cell must contain one or several different shapes in which the condition of homogeneity between these shapes is met in one organ, however, there may be more than one pattern or shape in the cells of one organ, as is the case in mammalian hepatic cells this phenomenon is called Phenomenon, "heterogeneity of mitochondria," and this difference may be attributed to the activity of the different cells. Mitochondria are filamentous, while cells in the central lobules contain a mixture of mitochondrial forms (granular and filamentous). Functions of mitochondria Mitochondria have many functions, including: 1 - Because it contains many respiratory enzymes, it is considered one of the respiratory centers for cell. 2- Mitochondria contain enzymes that perform a contradictory function, i.e. carry out a process construction in plant protozoa and catabolism in animal protozoa. 3 - It is believed that mitochondria are responsible for the production of zymogen granules in cells, therefore, the pancreas plays an important role in extracellular digestion. - 29 - 4 - Mitochondria play an important role in the process of fat metabolism. 5- Mitochondria play an important role in the formation of albuminuria in oocytes. 6- Mitochondria form the envelope of the axial filament of the mid segment of the sperm. 7-The main role of mitochondria is to produce the cell's energy currency, adenosine triphosphate (ATP), by phosphorylating adenosine diphosphate (ADP) through cellular respiration. 8-Mitochondria play a vital role in programmed cell death. Mitochondrial diseases Mitochondrial damage and resulting dysfunction is an important factor in a range of human diseases due to its influence on cell metabolism. Mitochondrial disorders usually manifest as neurological disorders such as autism. It can also manifest as: myopathy, diabetes, multiple endocrine disorders, and many other systemic disorders. Diseases caused by a mutation in mitochondrial DNA include Kearns-Sayre syndrome, MELAS syndrome and Leber hereditary optic neuropathy. In most cases, these diseases are transmitted by the mother to her children because the zygote gets its mitochondria - including mitochondrial DNA - from the egg. Diseases such as Kearns-Sayre syndrome, Pearson syndrome and chronic external progressive ophthalmoplegia are caused by large-scale mitochondrial DNA reorganizations, while others such as Melas syndrome, Leber hereditary optic neuropathy, MERRF and others are caused by mutations. Golgi apparatus In 1898, Camillo Golgi, while studying the nerve cells of some vertebrates, noticed the presence of a network or reticular structure, which he called the Golgi apparatus. Then many scientists conducted many studies that showed that all animal cells contain this structure. The Golgi apparatus is part of the endomembrane system in the cytoplasm. Structure Animal kingdom Animal kingdom are animals that contain a Vertebral column and are called vertebrates and other animals that do not contain - 31 - such a structure are known as Invertebrates 000 There are also two types of cells based on the number of chromosomes or genetic chromosomes, The first type contains the diploid number of genetic chromosomes (2n) and is called somatic cells, while the second type contains the haploid number of genetic chromosomes (n) and is called the reproductive cells or sex cells. Therefore, there is a Golgi apparatus in the somatic cells of vertebrates in the form of a network or reticular structure. Hence, this organ was described as a canal system (Gatinbi and Tohamy Moussa 1949), that is, it consists of vesicles and tubes whose cavity contains Golgi apparatus material 0, while The Golgi apparatus bears the shape of vesicles or crescents in the somatic and genital cells of invertebrates and the reproductive cells of vertebrates. The Golgi apparatus is also known as Lipochondria, Golgiosomes, or Dictyosomes. The Golgi apparatus is composed of units known as cisternae or elongated flattened sacs, a group of large vacuoles that lie at the edge of the cisterns, and clusters of small vesicles that exist between the large vacuoles. The Golgi apparatus of most eukaryotes consists of a group of flat, compact membranous vacuoles known as cisterns (also called synapses), arising from stacks of vesicles budding from the endoplasmic reticulum. Mammalian cells usually contain about 40 to 100 cisternae bundles. There are four to eight cisterns per bundle, but some protests have been observed with up to sixty cisterns. This group of cisternae is divided into three parts: conjugated, medial and unbranched forming two primary networks, the conjugate-Golgi network (CGN) and the branching-Golgi network. The coupled network (TGN) is the first cisterna and the transversal network is the last cisterna in which proteins are collected inside vesicles that leave for secretory vesicles or the cell surface. The Golgi apparatus tends to be larger in size and number in cells that synthesize and excrete large amounts of compounds. For example, a B cell that secretes immune system antibodies has many Golgi complexes. - 31 -  Structure of Golgi apparatus Types of Golgi apparatus vacuoles 1-Formative vesicles containing proteins whose destination is outside the cell. After aggregation, the vesicles bud and translocate directly to the plasma membrane and fuse with it, releasing their contents into the extracellular periphery in a process known as secretion. Antibodies secreted by B plasma cells. 2-Secretory vesicles are vesicles that contain proteins whose destination is outside the cell. After aggregation, the vesicles bud and are stored in the cell until signaled for secretion. Upon receiving this signal, the vesicles move towards the membrane and fuse with it to release their cargo. This process is known as regulated secretion. 3-Lysosomal vesicles containing proteins and ribosomes destined for the lysosome, a lysosome organelle containing several acid hydrolases, or lysosome-like storage organelles. These proteins include both digestive and membrane proteins. The vesicle first fuses with the entry and then the content is transferred to the lysosome by unknown mechanisms. Digestive proteases directed by lysosomes. Chemical composition The Golgi apparatus is composed of proteins and fats, and the fats are present in a masked form, that is, they are united with the proteins, but in a specific way, so that they do not give positive results when they are - 32 - dissolved in fat solvents or dyed with fat dyes, but in some cases In animals, fat is unmasked, as in the reproductive cells of annelids and molluscs, sex cells of Annelid & Mollusca. Pathological changes of the Golgi apparatus The Golgi apparatus is a vital organ that responds to different types of vital activities. Different physiological and pathological conditions affect the size, function, composition and location of the organ. Many morphological changes have been observed, including:- 1- Vitamin B complex deficiency causes the breakdown and fragmentation of the Golgi apparatus in mammalian neurons into small particles concentrated around the nucleus, and with continued deficiency of this vitamin, the Golgi apparatus continues to break down into particles that are difficult to see. 2- The Golgi apparatus of neurons migrates from its original location around the nucleus to the edge of the cell when the sciatic nerve is cut. 3- When cells are treated with pesticides, changes occur in the morphology of the Golgi apparatus, where the organ fragments, and continuous use of insecticides begins the Golgi apparatus gradually disappears. 4- The Golgi apparatus also breaks down into small particles when the cell is exposed to morphine poisoning, and with the continuity of morphine poisoning, the particles of the Golgi apparatus begin Golgi gradually disappear. Form, size and distribution Each type of animal cell contains a distinctive and special form of the Golgi apparatus, and this shape differs within a single cell according to its activity and also its age. But when the animal is fed, the Golgi apparatus returns to its normal shape, which it was in before the starvation process. Also, the Golgi apparatus breaks down into small particles when the cell enters the process of preserving the type. They spread evenly within the cytoplasm of the cell, and this leads to the distribution of these particles equally between the two cells resulting from the division process, although the size of the - 33 - Golgi apparatus varies from one cell to another. Depending on the type of cell and its activity, in active cells it is larger in size than in other cells that are less active. While the distribution of the Golgi apparatus inside the cells is constant and distinctive for each type of cell, for example it is spread in the cytoplasm as in the nerve cells of invertebrates or it is surrounding the central body as in the reproductive cells or in the form of a network surrounding the nucleus as in the neurons of vertebrates, as well as It is located between the nucleus and the excretory pole, as in the cells of the ductal glands. Function of Golgi apparatus 1- The Golgi apparatus is associated with the formation of secretions in different types of exocrine glands, such as the secretion of the enzyme pepsin by pepsin cells in the stomach, bile in hepatocytes, and zymogen in pancreatic cells. 2- The Golgi apparatus forms the apical body of the sperm. 3- The Golgi apparatus is the center of mucosal formation in mucosal cells. 4- The presence of vitamin A in animal cells is linked to the Golgi apparatus. For example, the Golgi apparatus secretes or concentrates vitamin A in mammalian thymocytes, while the Golgi apparatus isolates or separates vitamin A in renal cells. 5- The Golgi apparatus in gastric cells is specialized in the synthesis of fats from acids Fatty and glycerin. 6- The Golgi apparatus within the cells that make up the synovial membrane of the joints, associated with secretion Synovial fluid between joints. The Golgi apparatus plays a vital role in the formation of tooth enamel from cells Responsible for the formation of the year. 8- The Golgi apparatus is associated with the formation of colored or pigmented granules in the iris of the eye. 9- The Golgi apparatus plays an active role in preserving offspring by forming yolk sebum in oocytes. 10- The Golgi apparatus contributes to the secretion of the enzymes acid and alkaline phosphatase. - 34 - 11- The Golgi apparatus plays a role in the appearance of aging manifestations when the animal ages. 12- The Golgi apparatus is involved in the maturation of proteins and their subsequent release into cytoplasm. 13- The Golgi apparatus removes excess water from the secretory material formed and converted into cohesive granules. 14 - Did you know, my student brother 00, my student sister, that the Golgi apparatus is the factory? The only divine responsible for the synthesis of complex polysaccharides? 15- The Golgi apparatus plays an important role in the differentiation of embryonic cells, due to its presence in active state during cell differentiation. 16-The Golgi apparatus processes proteins coming from the endoplasmic reticulum, assembles them, and ships them to their various destinations inside and outside the cell. Endoplasmic reticular The electron microscope played an important and vital role in identifying the exact structure of the components of the cell. The ribbon membranes of the reticulum were first seen with an electron microscope in 1945 by in 1953 to describe the structure of these membranes. The endoplasmic reticulum is a cellular organelle found in eukaryotic cells that consists of an interconnected network of tubules, vesicles, and flat membrane sacs or tube-like units called cisterns. They are associated in certain regions with the plasma membrane and with the nuclear membrane in others. Membranes in the endoplasmic reticulum are an extension of the outer nuclear membrane. The endoplasmic reticulum is present in most types of eukaryotic cells but absent in red blood cells and sperm cells. There are two types of endoplasmic reticulum: the rough endoplasmic reticulum and the smooth endoplasmic reticulum. The outer face of the rough reticulum is studded with ribosomes which are the sites of protein synthesis. The rough reticulum is prominent and abundant in more cells, especially hepatocytes. The smooth reticulum does not have ribosomes on its surface and is few in most cells. It functions in the synthesis of lipids, the production of steroids and hormones, and the detoxification of natural - 35 - products of metabolism, alcohol and drugs. It is abundant in the cells of the testis, ovary and sebaceous gland. Rough endoplasmic reticulum The surface of the rough endoplasmic reticulum (also called the granular endoplasmic reticulum) is studded with protein-synthesizing ribosomes, giving it a "rough" appearance, hence its name. The site of attachment of the ribosome in the endoplasmic reticulum, however, the ribosomes are not stable parts of the structure of this organelle because they are in a continuous state of attachment and separation of the membrane. The ribosome binds to the rough reticulum only when a special protein-DNA complex is formed in the cytosol. This special complex is formed when a free ribosome begins translating mRNA for a protein whose target is the secretory pathway. Synthesis of enzymes for lysosomes and Synthesis of secreted proteins, either constitutively or systemically secreted. Smooth endoplasmic reticulum The smooth endoplasmic reticulum is sparse in most cells, and instead there are regions in the reticulum that are partly smooth and partially rough, and these regions are called the transitional endoplasmic reticulum because they contain sites for leaving the endoplasmic reticulum. Golgi apparatus. Specialized cells can have a lot of smooth lattice and in these cells smooth lattice has multiple functions, they synthesize lipids, phospholipids, and steroids. The cells that secrete these outgrowths such as those of the testis, ovary, and sebaceous gland have an abundant smooth endoplasmic reticulum. The smooth network also metabolizes carbohydrates, detoxifies natural metabolites, alcohol and drugs, and connects to receptors on cell membrane proteins and steroid metabolism. In muscle cells, it regulates the concentration of calcium ions. Allows for an increase in the area allocated for the storage of essential enzymes and the products of these enzymes. Secreted proteins are transported predominantly glycoproteins along the membrane of the endoplasmic reticulum. Because it does not have ribosomes, the endoplasmic reticulum is the cellular site for lipid and steroid synthesis, cellular detoxification, carbohydrate metabolism, and calcium ion storage. Cells specialized in secreting hormones tend to be abundant in the smooth endoplasmic reticulum. Likewise, liver detoxification cells are rich in smooth endoplasmic reticulum. The smooth endoplasmic reticulum is also the - 36 - cellular storage site for toxic calcium ions. It even contributes to Alzheimer's disease and many genetic skeletal disorders cause abnormal bone growth, weak joints, and susceptibility to joint dislocation and the endoplasmic reticulum occasionally induces apoptosis in response to an increased amount of unfolded proteins. Ribosomes The ribosome is an organelle of living cells that is composed of ribosomal proteins and ribosomal RNA. Its main job is to translate messenger RNA into peptide chains that are then cross-linked to form proteins. Thus, it is one of the important centers in the process of converting genetic information into proteins encoded within the genetic formula. Ribosomes consist of two protein units, which do not come together except in the case of protein formation. One of these units is larger than the other, these two units come together when the ribosome is ready to make a new protein. The ribosome is the factory that converts the encoded genetic information into a peptide sequence of amino acids. Ribosomes can swim in the cell freely, as in prokaryotes. In eukaryotes, however, they may be found free in the cytoplasm or attached to the cytoplasmic face of the endoplasmic reticulum membranes (specifically rough) or attached to the nuclear envelope. The ribosomes scattered in the cytoplasm produce the proteins of the cell. As for the ribosomes that are linked to the endoplasmic reticulum and the nuclear envelope, they produce the proteins of the cell membrane or those that may not belong to the cell itself, such as hormones. The ribosome is made inside the nucleus of the nucleus. And once it is manufactured, it is sent out of the nucleus through the pores in the nucleus membrane.Ribosomes differ from most organelles in that they are not - 37 - surrounded by a protective membrane. The main job of the ribosome is to make proteins for the cell. There can be hundreds of proteins that must be made for a cell, so the ribosome needs specific instructions on how to make each type of protein. And these instructions come from the nucleus in the form of RNA. Types of ribosomes 1-Prokaryotic cell ribosomes: They are smaller than the ribosomes in eukaryotic cells. It consists of 70S units (S=Svedberg-Unit). The minor unit is 30S and the major unit is 50S. The S unit is not additive, it expresses the centrifugal force of these particles. 2-Eukaryotic cell ribosomes consists of 80S units, with the largest unit being 60S and the smallest unit being 40S. The two ribosome units combined represent approximately 4.2 atomic mass units. It contains approximately 85 proteins and 3 rRNA. Structure of ribosome Large (red) and small (blue) subunit fit together Lysosomes It was discovered in 1949 by the Belgian scientist Christian de Duffy. It initially consists of adding hydrolytic enzymes to endosomes produced from the Golgi apparatus. The size of lysosomes ranges from 0.1 μm to 1.2 μm. With a pH ranging from 4.5 to 5.0, the interior of the lysosomes is acidic compared to the cellular fluid, pH 7.2. Lysosomes are organelles found in animal cells that contain digestive enzymes that break down excess or dead organelles, food, viruses, and bacteria. The lysosome is surrounded by a membrane that has a very important role in the functioning of the organelles. They are semi-spherical, membranous organelles found - 38 - in the cell, similar in function to the work of the human digestive system, as they contain active enzymes. Lysosomes convert complex substances such as fats, carbohydrates and foreign bodies into simple substances that facilitate their absorption. Lysosomes are found in almost all animal cells, and are found abundantly in cells that carry out swallowing activity, such as macrophages and white blood cells. It is noted that the proteins of the lysosomal membrane are glycosylated, which works to protect this membrane from the influence of enzymes that digest proteins present inside the lysosomes. Lysosomal enzymes are built up in the endoplasmic reticulum, then transported to the Golgi apparatus, where they are processed. Vesicles laden with these lytic enzymes travel from the mature face of the Golgi apparatus. These vesicles are known as primary lysosomes. During the process of phagocytosis, bodies are taken from outside the cell to the inside of it in vesicles surrounded by a membrane, which are called "violating phagocytic bodies". Irregular in shape, with inhomogeneous content. Diagram of Lysosomes Size and distribution of Lysosomes Lysosomes are located wherever there are units of the Golgi apparatus, as there is a close relationship between the lysosomes and the location of the Golgi apparatus in the cell. Studies have shown that primary lysosomes arise partially from the Golgi apparatus, and therefore it is natural that the location of the lysosomes is concomitant with the location of the Golgi apparatus in the cell. The size of the lysosomes varies Depending on the type and activity of the cell, the more active the cell is, the more it contains lysosomes of large sizes. - 39 - Types of lysosomes Four types of lysosomes can be distinguished: 1- Original or primary lysosomes It means how to form lysosomes. The ribosomes that are found on the membrane of the endoplasmic reticulum synthesize the enzyme acid phosphatase and collect it inside the lumen of the endoplasmic reticulum, then this enzyme is carried out outside the endoplasmic reticulum and is assembled inside the small vesicles of the Golgi apparatus This structure (a small vesicle containing the enzyme acid phosphatase) is known as the primary lysosome. Accordingly, it can be said that the primary lysosomes partially originate from the Golgi apparatus. 2-The secondary lysosomes (Digestive vacuoles or heterophagosomes) This type of lysosomes engulfs the foreign organisms that enter the cell and fragments and destroys them with the enzyme acid phosphatase, and in the end the products of the fragmentation process pass through the lysosome membrane to the cytoplasm of the cell, and thus this type of lysosomes acts as a means of defense for the cell. 3-The autophagy lysosomes This type of lysosomes engulfs parts of the cell such as the mitochondria, the endoplasmic reticulum, the Golgi apparatus, and so on. This process may lead to cell death, so this type of lysosomes is known as suicide cysts. 4-The residual lysosome bodies It means the lysosomes that contain undigested residual materials, where these lysosomes break down these materials into small particles that the cell can get rid of. - 41 -  Lysosomes also help to defend against Pathogen Behaviour of lysosomes Lysosomes are affected by many abnormal factors, physiologically and structurally, as follows: 1- If the lysosomes are exposed to X-rays, they accumulate in some cells such as nerve cells, or they fragment and disappear in another type of cells such as hepatocytes, while exposing the cells to X-rays for long periods leads to the explosion of the plasma membranes of the cells. 2- Starving the animal leads to a decrease in the number of lysosomes, and as the starvation continues, the lysosomes disappear completely from the cells. 3- When cells prepare to enter the aging phase, this is accompanied by a decrease in the number of lysosomes, especially in hepatocytes. 4- Infection of cells with some diseases leads to a decrease in the number and size of lysosomes. An example of this is the liver cell, when it is infected with cancer, the number of lysosomes decreases. Functionl significance of lysosomes 1- Lysosomes participate in the intracellular digestion process and the formation of colored fat granules 0 2- Lysosomes play an essential role in the metabolism of carbohydrates, as they are abundantly present in cells during the metabolism of carbohydrates. 3- Lysosomes play an essential role in getting rid of excess tissue from the animal's body by swallowing it 4- Lysosomes help in the process of facilitating the entry of the sperm into the egg. 5- Lysosomes have a close connection with many biological and pathological phenomena such as morphogenesis, aging, and the transformation of normal cells into cancer cells. Nissl bodies Nissl in 1889 was the first to talk about these tiny organelles, explaining that these bodies are found only in nerve cells. These bodies were described as colored bodies or basal bodies due to their strong susceptibility to dyeing - 41 - with basal dyes, and these bodies are not found only in nerve cells, so these bodies are distinguished for nerve cells from others. The offspring's bodies occupy two of the three sites within the nerve cell in each of the cytoplasm and dendrite branches, while they lack presence in the axons of these cells. Chemical composition of Nissl bodies The bodies of the offspring consist of a nuclear protein, the nuclear protein is a simple protein such as histamine and nucleic acid RNA, and this is similar to ribosomes that have the same structure, that is, a nuclear protein, but the type of protein is different, Nuclear Be a ribosome so it becomes a ribosome, Be granules or the body of an offspring He said listen and obey And there is a difference between the function of the ribosome and the body of the offspring. Demonstration of Nissl bodies We and you, my student brother and sister, can witness the greatness of the Creator, Glory be to Him, the Most High, represented in the presence of such minute organelles within a precise structure (the cell) that can only be seen with binoculars or an optical microscope from two images. Intervention from a human being, and the cell was not stained with any type of dye, by means of a contrast microscope 000 second, and the cell was fixed by a fixative that does not dissolve the bodies of the offspring, then the cell was dyed with a dye that deals only with the bodies of the offspring, such as toluidine blue or Gimsa dye. Physiological signifance of Nissl bodies Some workers in the field of scientific research may not give importance to these bodies on the grounds that they are limited to one type of cell 000 and this is the big mistake 0 why? And the answer is crystal clear in its orbit 00 and it is that the nerve cell is not like any type of cell as it consists of the nervous system that controls and controls all the vital processes that occur within the body of the organism 0 and from this concept we must recognize the physiological importance of bodies offspring, which are as follows:- 1- Some researchers believe that these bodies store oxygen in nerve cells, and therefore it was concluded that there is a close relationship between these bodies and the functional activities of these cells, through the stressful situations that the animal is exposed to, and with which these - 42 - bodies disappear and return again when something happens. Is the animal resting? 2- The bodies of the offspring are affected by the physiological state of the nerve cell 00. When the nerve is cut, for example, the bodies of the offspring disappear after a few days, and also the amount of nucleic acids decreases to a very large extent, and this indicates that the bodies of the offspring have a close relationship with the process of the presence of nuclear proteins and the motor and sensory functions of the nerve cell. 3- The migration of the bodies of the offspring from their original areas of existence to the axon of the nerve cell after its death is clear and supportive evidence to say that the bodies of the offspring store oxygen, as the migration of these bodies is nothing but a search for oxygen. The center body Cleveland (1953) was able to observe it by means of a light microscope in fibrous cells during their division, noting special behavior, general characteristics, and a tendency to a certain type of pigment. All this confirms the fact that it is present in the cytoplasm.The centrosome is one of the cytoplasmic living organelles inside the cell. It is also known as the center of division. It is found in all animal cells except fully formed red blood cells. It plays an important and vital role in the process of cell division. The centrosome is found in the interstitial cell close to the nucleus and sometimes It occupies the geometric center of the cell and in spite of this, the centrosome has a distinctive location specific to each type of animal cell. During division, the centrosome divides into two parts that migrate to the opposite poles of the achromatic spindle, and there each part is surrounded by a wide clear region called the centrosome, which in turn merges externally into the stellar sphere. Knowledge about the chemical composition, or the exact function of these different structures is still little. Centrosomes are attached to the nuclear membrane during the prophase of the cell cycle. During mitosis, the nuclear membrane breaks down, and tubules around the centrosome can then interact with chromosomes to form the mitotic spindle. The centrosome is replicated once in each cell cycle, so each daughter cell inherits one centrosome, which contains two structures called centrioles. The centrosome replicates during the S phase of the cell cycle. During prophase in the process of cell division, the two centrosomes migrate to opposite cytosolic poles of the cell. A cleavage - 43 - spindle then forms between the two centrioles. When dividing, each daughter cell takes on one centrosome. The presence of an abnormal number of centrosomes in the cell is associated with the occurrence of cancers. Structure of center body The centriole consists of a pair of interconnected centrioles. The centrioles contain cylindrical arrays of 9 groups of triangular microtubules organized in a circular manner. The centrosome contains a mature centriole called the mother centriole and an immature centriole assembled during the previous cell cycle, the nascent centriole, which is about 80% of the length of the mother centriole, which are believed to be necessary for stabilization of microtubules in the centriole and for anchoring of centrioles to the plasma membrane during mitosis. Centrosome function The centrosome is the main center for organizing microtubules in human cells and is a very small, yet very important cellular organelle for basic cellular functions, located adjacent to the nucleus. Structure of center body Function of center body The main role of the centrosome is as follows: 1-Intracellular organization of microtubules during cell division. 2-The centrosome serves for the proper formation and orientation of spindle filaments to carry out mitosis, ensuring proper segregation of the sister chromatids of each daughter cell. 3-Control of cellular shape, polarity, reproduction, motility, and cell division. - 44 - 4-Coordination of a variety of cellular processes, including cell movement, signaling, adhesion and movement of proteins by the micro-cytoskeleton and cell polarity. 5-Determine the pathways by which different cellular components can be transported to different parts of the cell. 6-Help determine the speed at which components move along transport pathways, and act as a signaling center to modify certain components before they are transported to their destinations. 7-Regulating the process of phagocytosis through the role of centrioles in changing the shape of the cell membrane. The role of center body in cell division The centrosome and its role in mitosis, the centrosome cycle consists of 4 main phases in both phases, the interphase and the mitotic phase as follows: G1 stage in which the centrosome is duplicated. G2 stage in which the centrosome matures. The first stages of mitosis (pre-anaphase) where the separation of the two centrioles occurs. The last stages of mitosis (anaphase) in which the chromosomes separate with the help of centrosomes. The centrosome is of great importance in organizing cell division, and regulating the transition between the stages of division in interphase, the most important of which is the transition from the G1 stage to the S phase. In the absence of centrioles, the accuracy of cell division decreases as problems such as meiosis and unequal cell divisions occur, which It leads to chromosomal mutations and sometimes the development of cancer cells. Cilia and Flagella Cilia and flagella were discovered by the scientist Antonie van Leeuwenhoek in the late seventeenth century. After the development of the microscope, non-motile cilia, most of which are found in animals, were observed in almost all types of cells. Cilia range from 1-10 micrometers, while the flagellum is 20–50 micrometers in length. Some cilia are also found in plant cells in the form of gametes. Cilia and flagella are two different types of microscopic appendages on cells. Cilia are found in both animals and microorganisms. Bacteria and eukaryotic gametes use flagella - 45 - for locomotion. Cilia and flagella serve the functions of movement in the cell, but in different ways, and both depend in their work on Diane - a motor protein - and microtubules. Cilia and flagella are organelles in cells that perform propulsion functions, sensory organs, cleaning mechanisms, and many other important functions in living organisms. Cilia flagella consist of 9 groups of microtubules, each group is two tubes, and in the center there is a pair of tubular groups in an arrangement called the ciliary axoneme, which is covered by the plasma membrane. Function of cilia and flagella 1-The cell body synthesizes ciliary proteins and transports them to the head of the axonal filament. This process is called intraciliary transport or intraflagellar transport. Scientists currently believe that about 10% of the human genome is dedicated to cilia and their genesis. 2-These hair-like organelles move cells and transport materials. It can also transport fluids in marine organisms, such as oysters, to enable them to transport food and oxygen. Cilia contribute to respiration by preventing debris and potential pathogens from invading the body. 3-Cilia and flagella play an active role in the life cycle of the cell and also play an important role in cellular communication. Peroxisomes Peroxisomes are small vesicles, single membrane-bound organelles found in the eukaryotic cells. They contain digestive enzymes for breaking down toxic materials in the cell and oxidative enzymes for metabolic activity. They are a heterogeneous group of organelles and the presence of the marker enzymes distinguished them from other cell organelles. Peroxisomes play an important role in lipid production and are also involved in the conversion of reactive oxygen species such as hydrogen peroxide into safer molecules like water and oxygen by the enzyme catalase. Mostly peroxisomes occur as an individual organelle, e.g. in fibroblasts. They also exist in the form of interconnected tubules in liver cells known as peroxisome reticulum. - 46 - Peroxisome Structure Peroxisomes vary in shape, size and number depending upon the energy requirements of the cell. These are made of a phospholipid bilayer with many membrane-bound proteins. The enzymes involved in lipid metabolism are synthesized on free ribosomes and selectively imported to peroxisomes. These enzymes include one of the two signaling sequences- Peroxisome Target Sequence one being the most common one. The phospholipids of peroxisomes are usually synthesised in smooth Endoplasmic reticulum. Due to the ingress of proteins and lipids, the peroxisome grows in size and divides into two organelles. Peroxisomes do not have their own DNA. Proteins are transported from the cytosol after translation. Peroxisome Function The main function of peroxisome is the lipid metabolism and the processing of reactive oxygen species. Other peroxisome functions include:  They take part in various oxidative processes.  They take part in lipid metabolism and catabolism of D-amino acids, polyamines and bile acids.  The reactive oxygen species such as peroxides produced in the process is converted to water by various enzymes like peroxidase and catalase.  In plants, peroxisomes facilitate photosynthesis and seed germination. They prevent loss of energy during photosynthesis carbon fixation. Metabolism of Peroxisomes Isolated peroxisomes are permeable to small molecules such as sucrose. During the isolation process, they often lose proteins that are normally confined to the peroxisomal matrix. In all living cells, peroxisomes are the sealed vesicles surrounded by a single membrane. Cytoskeleton The cytoskeleton of a cell is made up of microtubules, actin filaments, and - 47 - intermediate filaments. These structures give the cell its shape and help organize the cell's parts. In addition, they provide a basis for movement and cell division. For instance, cilia and (eukaryotic) flagella move as a result of microtubules sliding along each other. The cytoskeleton is a structure that helps cells maintain their shape and internal organization, and it also provides mechanical support that enables cells to carry out essential functions like division and movement. There is no single cytoskeletal component. Rather, several different components work together to form the cytoskeleton. The cytoskeleton of eukaryotic cells is made of filamentous proteins, and it provides mechanical support to the cell and its cytoplasmic constituents. All cytoskeletons consist of three major classes of elements that differ in size and in protein composition. Microtubules are the largest type of filament, with a diameter of about 25 nanometers (nm), and they are composed of a protein called tubulin. Actin filaments are the smallest type, with a diameter of only about 6 nm, and they are made of a protein called actin. Intermediate filaments, as their name suggests, are mid-sized, with a diameter of about 10 nm. Unlike actin filaments and microtubules, intermediate filaments are constructed from a number of different subunit proteins. In many types of cells, networks of actin filaments are found beneath the cell cortex, which is the meshwork of membrane-associated proteins that supports and strengthens the plasma membrane. Such networks allow cells to hold — and move — specialized shapes, such as the brush border of microvilli. Actin filaments are also involved in cytokinesis and cell movement. Intermediate filaments come in several types, but they are generally strong and ropelike. Their functions are primarily mechanical and, as a class, intermediate filaments are less dynamic than actin filaments or microtubules. Intermediate filaments commonly work in tandem with microtubules, providing strength and support for the fragile tubulin structures. All cells have intermediate filaments, but the protein subunits of these structures vary. Some cells have multiple types of intermediate filaments, and some intermediate filaments are associated with specific cell types. - 48 -  Nucleus The first person to discover the nucleus was the scientist Leeuwenhoek in 1700, then Robert Brown came after him in 1831, confirming that the nucleus is an essential and permanent part of the cell. Since then, studies have been continuing on the anatomical and functional components of the cell. A nucleus, as related to genomics, is the membrane-enclosed organelle within a cell that contains the chromosomes. An array of holes, or pores, in the nuclear membrane allows for the selective passage of certain molecules (such as proteins and nucleic acids) into and out of the nucleus. The nucleus is one of the most obvious parts of the cell when you look at a picture of the cell. It's in the middle of the cell, and the nucleus contains all of the cell's chromosomes, which encode the genetic material. So this is really an important part of the cell to protect. The nucleus has a membrane around it that keeps all the chromosomes inside and makes the distinction between the chromosomes being inside the nucleus and the other organelles and components of the cell staying outside. Sometimes things like RNA need to traffic between the nucleus and the cytoplasm, and so there are pores in this nuclear membrane that allow molecules to go in and out of the nucleus. It used to be thought that the nuclear membrane only allowed molecules to go out, but now it's realized that there is an active process also for bringing molecules into the nucleus. The shape of the nucleus The shape of the nucleus is often linked to the shape of the cell. As a general rule, most of the nuclei are spherical or oval in shape, and this does not preclude the presence of the nucleus in other shapes: elongated, clustered, sticky, pyramidal, pear-shaped, renal, etc. Nucleus size Often the size of the nucleus is not fixed or changes frequently. Despite this, there is a general relationship between the size of the nucleus and the size of the cytoplasm of the cell. This relationship is known as the cytoplasmic nuclear coefficient (SN). This means that the cytoplasmic nuclear coefficient has a constant value, meaning that the increase in the volume of The nucleus must be followed by an increase in the size of the cytoplasm, and when there is a failure to maintain the constant value of this coefficient, it is an indication that the cell has entered the process of division. - 49 - Number of nucleus inside the cell The normal image of a cell is that it contains one nucleus, but not all cells have the normal number of nuclei. Some of them contain two nuclei (liver cells, nerve cells, and cartilage cells), and some of them contain a cellular compact, i.e. more than two nuclei, as in bone cells. Bone cells that are found in the bone marrow and also striated muscle fibers. Nucleus location It is natural that the nucleus does not exist in one location within the cell, and this is due to the different types of cells, but it is distinct and constant in one type of cell 0 and the nucleus inside the cell has a number of sites 000 Think with me after you put the nucleus in the center of the cell as a location other than this? Structure The nucleus goes through two stages in its life history: A- The interphase, and it is called the metabolic phase, and it means the period that comes between each two successive divisions, and therefore it is called the “resting phase.” This does not mean a total resting phase of the nucleus, but resting on division only, and the nucleus performs all its functions except for division. B- The stage of division, which means the period of division in the cell, i.e. the period occupied by the different stages and forms of division. The nucleus is a spherical-shaped organelle that is present in every eukaryotic cell. The nucleus is the control center of eukaryotic cells. It is also responsible for the coordination of genes and gene expression. The structure of the nucleus includes nuclear membrane, chromosomes, nucleoplasm, and nucleolus. The nuclear envelope, also known as the nuclear membrane, is made up of two lipid bilayer membranes that in eukaryotic cells surround the nucleus, which encloses the genetic material. The nuclear envelope consists of two lipid bilayer membranes: an inner nuclear membrane and an outer nuclear membrane. The space between the membranes is called the perinuclear space. It is usually about 10–50 nm wide. The outer nuclear membrane is continuous with the endoplasmic reticulum membrane. The nuclear envelope has many nuclear pores that allow materials to move between the cytosol and the - 51 - nucleus. Intermediate filament proteins called lamina form a structure called the nuclear lamina on the inner aspect of the inner nuclear membrane and give structural support to the nucleus. The inner nuclear membrane encloses the nucleoplasm, and is covered by the nuclear lamina, a mesh of intermediate filaments which stabilizes the nuclear membrane as well as being involved in chromatin function. It is connected to the outer membrane by nuclear pores which penetrate the membranes. While the two membranes and the endoplasmic reticulum are linked, proteins embedded in the membranes tend to stay put rather than dispersing across the continuum. It is lined with a fiber network called the nuclear lamina which is 10-40 nm thick and provides strength.The nuclear envelope is punctured by around a thousand nuclear pore complexes, about 100 nm across, with an inner channel about 40 nm wide. The complexes contain a number of nucleoporins, proteins that link the inner and outer nuclear membranes. Chromatin Chromatin can exit as either euchromatin or heterochromatin. Euchromatin is the form of chromatin present during gene expression, and has a characteristic ‘beads on a string’ appearance. It is activated by acetylation. In contrast, heterochromatin is the ‘inactive’ form, and is densely packed. On electron microscopy, euchromatin stains lighter than heterochromatin which reflects their relative densities. Nucleolus The nucleolus is the site of ribosome and ribosomal RNA production. On microscopy, it appears as a large dense spot within the nucleus. After a cell divides, a nucleolus is formed when chromosomes are brought together into nucleolar organizing regions. During cell division, the nucleolus disappears. Nucleus Function Following are the important nucleus function:  It contains the cell’s hereditary information and controls the cell’s growth and reproduction.  The nucleus has been clearly explained as a membrane-bound structure that comprises the genetic material of a cell. - 51 -   It is not just a storage compartment for DNA, but also happens to be the home of some important cellular processes.  First and foremost, it is possible to duplicate one’s DNA in the nucleus. This process has been named DNA Replication and produces an identical copy of the DNA.  Producing two identical copies of the body or host is the first step in cell division, where every new cell will get its own set of instructions.  Secondly, the nucleus is the site of transcription. Transcription creates different types of RNA from DNA. Transcription would be a lot like creating copies of individual pages of the human body’s instructions which may be moved out and read by the rest of the cell.  The central rule of biology states that DNA is copied into RNA, and then proteins. Shapes and sizes of animal cells Most animal cells range in size from 10 to 100 microns. The size and shape of cells in organisms varies greatly. The difference reaches its deepest when we find that there are thousands of shapes, types and sizes of cells in a single organism originating from a single cell. It seems that this difference in the size and shape of cells is due to important reasons such as age, location of cells and their embryonic development, as well as function, which is of great importance in determining size and shape. Types of animal cells shaped For example, red blood cells have a disc-shaped shape that helps them pass through narrow blood vessels. - 52 -  Red Blood cells Neurons are characterized by their large size and the presence of many prominent appendages from the cell body, in addition to the presence of a long prominent protrusion that is associated with other neurons located far away in another location, and thus they can transmit thousands of nerve messages through their dendrite appendages associated with thousands of axons of other neurons. Fat cells and eggs are among the largest cells in size, due to the presence of a lot of nutrients stored in these cells. Nerve