Zoology 11101 Lecture 1 PDF

Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Lecture 1 Introduction The world is estimated to have 5 to 30 milli...

Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Lecture 1 Introduction The world is estimated to have 5 to 30 million species of living organisms. At present, about 2.5 million species of living organisms have been given scientific names. Over 1.5 million of them are animal species and out of which 750,000 belong to insect species alone. There are 350,000 species of plants including algae, fungi, mosses and higher forms of plants. Thus the existence of different forms of a species or genus and diverse adaptations for, varied surroundings are referred to as “biodiversity”. Zoology Zoology or animal biology is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, taxonomy & classification, habits, and distribution of all animals, both living and extinct, and how they interact with their ecosystems. The term is derived from Ancient Greek. Concept of Cell Biology All organisms are composed of cells, the smallest units of living matter.  Cells are capable of self-reproduction, and existing cells come only from preexisting cells.  Cells are very small and are measured in micrometers.  Cells must remain small in order to have an adequate amount of surface area to volume. Zoology 11101 1 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE These generalized statements are known as Cell theory. This theory was forwarded by Mathias Schleiden and Theodor Schwann in 1838 - 39. The cell theory includes four more ideas:  The cells are the building block of structures in living things  The cell is derived from other cells by division  The cell contains information that is used as instructions for growth, development and functioning  The cell is the functioning unit of life; the chemical reactions of life take place within cells. The study of the structure of cells (cytology) is part of a major branch of biology known as cell biology. Due to its wide application many new branches have sprung up in biology. Some of the new branches related to cytology are, Cytotaxonomy, Cytogenetics, Cell physiology, Cytochemistry, Molecular Biology, Cytopathology and Cytoecology. Cell Structure and Function The eukaryotic cell is much more complex and it contains many membrane bound organelles to perform specific functions. It contains a nucleus isolated from cytosol and enclosed in a well defined double membrane. Zoology 11101 2 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Table 1: Summary of the differences between Prokaryotic and Eukaryotic Cells Zoology 11101 3 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE A typical eukaryotic animal and plant cell is shown and the difference between these types of cells is given in Table 2. Table 2 The Cell Membrane (or Plasma Membrane) It is the outer limiting membrane of both prokaryotic and eukaryotic cells. It is ultra thin, elastic, living membrane. It could be observed only under electron microscope. Singer and Nicholson (1972) have proposed a fluid mosaic model for the plasma membrane. The fluid mosaic membrane is a dynamic structure and selective transport barrier. In this structure much of the protein molecules float about. Some of them are anchored to the organelles within the cell. Lipid molecules also move about. ‘Fluid mosaic model’ is applied to all biological membranes in general. Zoology 11101 4 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE The cell membrane controls the passage of materials both into and out of the cell. It regulates the passage of water and dissolved substances. Water passes through the membrane by Osmosis. Water soluble substances cross the membrane by diffusion or by active transport. Many water soluble solutes are transported by carrier proteins. Lipid soluble compounds pass more quickly by dissolving in the phospholipid layer. Nucleus The nucleus is the most important organelle of cell. It controls all metabolic processes and heredita activities of the cell. The nucleus was first discovered and named by Robert Brown in 1833. The occurrence of a nuclear membrane was first revealed by O. Hertwig in 1893. The nucleus is found in all the eukaryotic cells of plants and animals. However some eukaryotic cells such as the sieve tubes of higher plants and mammalian erythrocytes have no nucleus. Usually the cells contain single nucleus (mononucleate). However certain cells may have more than one nuclei. Accordingly they may be called binucleate or polynucleate cells. The polynucleate cells of the animals are called syncytial cells (Osteoblast cells) The shape of the nucleus may be spherical, elliptical or discoidal. In certain cells the nucleus is irregular in shape. The size of the nucleus may vary from 3 μm to 25 μm in diameter. The size is directly propotional to that of the cytoplasm. Nuclear size may also be determined by the number of chromosomes. The nucleus of the haploid cells are smaller than that of the diploid cells. The nucleus is surrounded by a nuclear envelope. This envelope is comprised of two membranes of 5-10 nm thickness. The inner nuclear membrane supports a fibrous sheath called the nuclear lamina. The inner nuclear membrane is surrounded by the outer nuclear membrane. The space between the inner and outer membranes is known as perinuclear space. It is a 10 to 50 nm wide fluid filled compartment. The nuclear lamina is a protein meshwork. It is a very dynamic structure. The nuclear envelope is perforated by nuclear pores. Each pore has a diameter between 10 nm to 100 nm. It has been calculated that the nuclear pores account for 5 to 15 percent of the surface area of the nuclear membrane. There is continous movement of molecules across the nuclear envelope Zoology 11101 5 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE through the pores. The nucleus is filled with a transparent semisolid matrix known as nucleoplasm or nuclear sap. The chromatin threads and the nucleolus remain suspendended in the nucleoplasm. The nucleoplasm is composed of nucleoproteins, proteins, enzymes and minerals. It contains several thread like coiled structures. These are the chromatin fibres. During the cell division they become thick ribbon like structures known as chromosomes. The chromatin is made up of Deoxy - ribose nucleic acid (DNA) and proteins. The nucleus contains one or more spherical colloidal structures called nucleoli. The size of nucleolus is related to the synthetic activity of the cell. The number of nucleoli in the cells may be one, two or four. Chemically, nucleolus contains DNA of nucleolar origin, four types rRNA, 70 types of ribosomal proteins, RNA binding proteins and RNA splicting nucleoproteins. Ribosomal subunits are synthesized in the nucleolus. Initiation, production and maturation stages of ribosomal formation happen in three distinct regions of the nucleolus. Chromosomes The chromatin fibres get condensed into chromosomes during cell divisions. They are capable of self-reproduction and they play an important role in heredity. The size of a chromosome can be measured during mitotic metaphase. It may range from 0.25 μm to 30 μm. Chromosomes and their role in cell division were first explained by A. Schneider (1873). In 1887 Benden and Bovery reported that the number of chromosomes for each species is constant. The reproductive cells such as sperm or ovum has one set of chromosomes and it is known as the haploid set(n). It is also known as the genome. The somatic or body cells contain two haploid set or genomes and are known as the diploid cells (2n). The diploid condition is arrived at by the union of the haploid male and female gametes in the sexual reproduction. Number of Chromosomes Common name Scientific name Chromosome Number Paramecium P. aurelia 30-40 Hydra H. vulgaris 32 Fruit fly Drosophila sps 8 Pigeon Columba livia 80 Man Homo sapiens 46 The shape of the chromosome changes from phase to phase. Each chromosome has a clear zone, known as centromere or kinetocore along their length. The centromere divides the chromosome into two parts. Each part is called the chromosome arm. Thus according to the Zoology 11101 6 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE position of the centromere and nature of the chromosome arm, the chromosomes may be Telocentric, Acrocentric, Submetacentric and Metacentric. Ribosomes The ribosomes are small dense, rounded and granular particles. They contain ribonucleoprotein. They occur either freely in the matrix of the mitochondria, chloroplast (in plant) and cytoplasm or remain attached with the membrane of the endoplasmic reticulum and nucleus. The ribosomes were described by G. Palade in 1952. The name ‘ribosome’ was coined by R. Roberts in 1958. The ribosomes occur in both prokaryotic and eukaryotic cells. In the cells in which active protein synthesis takes place, the ribosomes remain attached with the membranes of the endoplasmic reticulum. The cells where such active synthesis happens are pancreatic cells, hepatic cells, osteoblasts, serous cells of submaxillary gland, chief cells of the glandular stomach, thyroid cells and mammary gland cells. The ribosomes are spheroid structures with a diameter of 150 to 250 Å. Each ribosome is composed of two subunits. One subunit is large in size and has a dome like shape. The other ribosomal subunit is smaller in size and it occurs above the larger subunit forming a cap-like structure. The ribosomes are chemically composed of RNA and proteins. The ribosomal RNA (rRNA) plays a central role in the process of protein synthesis. The ribosomal proteins enhance the catalytic function of the rRNA. The functioning of rRNA is under genetic control. Mitochondria The mitochondria are filamentous or granular cytoplasmic organelles of all aerobic cells of higher animals and plants. They are also found in micro-organisms including Algae, Protozoa… Zoology 11101 7 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE In 1850, Kolliker observed as granular structures in the striated muscles. The name ‘mitochondria’ was given to them by Benda (1897-98). Sir Hans Adolph Krebs, in 1937 found out various reactions of citric acid cycle. Kennedy and Lehninger (1948-50) showed that Citric acid cycle, oxidative phosphorylation and fatty acid oxidation took place in the mitochondria. The number of mitochondria in a cell depends on the type and functional state of the cell. Certain cells contain large number of mitochondria e.g., eggs of sea urchin contain 140,000-150,000 mitochondria. Oocytes of amphibians contain 300,000 mitochondria. Liver cells of rat contain only 500- 1600 mitochondria. They vary in size from 0.5 μm to 2.0 μm. Due to their minute nature they cannot be seen under light microscope. Each mitochondrion is bound by two highly specialized membranes. The outer membrane is smooth. It is separated from the inner membrane by a 6-8 nm wide space. The inner membrane is highly convoluted, forming a series of enfolding known as cristae. Thus mitochondria are double membrane envelopes. The inner membrane divides the mitochondrial space into two distinct chambers. The outer compartment is the peri- mitochondrial space. It is found between outer and inner membranes. The inner compartment is the matrix space. It is filled with a dense gel like substance called mitochondrial matrix. The matrix contains lipids, proteins and circular DNA molecules. The outer and inner membranes, intermembrane space and mitochondrial matrix contain several enzymes. Hence the mitochondria perform several important functions such as oxidation, dehydrogenation, oxidative phosphorylation and respiratory chain of the cell. Mitochondaria play a key role in the oxidation of carbohydrates and fats, they are considered as the actual respiratory organs of the cells. During such biological oxidations large amount of energy is released. The energy is utilized by the Zoology 11101 8 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE mitochondria for synthesis of the energy rich compound known as adenosine tri phosphate or ATP. Due to this function, the mitochondria are also known as “power houses” of the cell. In animal cells mitochondria produce 95 % of ATP molecules. Endoplasmic Reticulum (ER) Electron microscopic study of sectioned cells has revealed the presence of a three dimensional network of sac-like and tubular cavities called cisternae bounded by a unit membrane inside the cell. Since these structures are concentrated in the endoplasmic portion of the cytoplasm, the entire organisation is called the endoplasmic reticulum. This name was coined by Porter in 1953. The occurrence of ER varies from cell to cell. They are absent in erythrocytes, egg cells and embryonic cells. The ER is the site of specific enzyme controlled biochemical reactions. Its outer surface carries numerous ribosomes. The presence of ribosomes gives a granular appearance. In this condition ER is described as rough endoplasmic reticulum (RER). RER is the site of synthesis of proteins. Ribosomes are absent on smooth endoplasmic reticulum (SER). SER is concerned with lipid metabolism. Morphologically ER may occur in three forms namely 1. Lamellar form 2. Vesicular form and 3. Tubular form. Lamellar form or Cisternae : These are long, flat, sac like tubules. Their diameter is about 40- 50 μm. The RER has a synthetic role. It is mostly seen in cells of pancreas, notochord and brain. Vesicles :- These are oval, vacuolar structures. Their diameter is about 25-500 μm. They occur in most of the cells. Tubules :- These are branched structures forming the reticular system along with the cisternae and vesicles. They have a diameter of 50-190 μm. They occur in almost all cells. Functions :- 1. It provides skeletal framework to the cell. 2. It facilitates exchange of molecules by the process of osmosis, diffusion and active transport. 3. Enzymes of ER control several metabolic activities. 4. They serve as intracellular transporting system. 5. It conducts intra-cellular impulses. 6. It helps to form nuclear membrane after cell division. 7. SER synthesises lipids. Zoology 11101 9 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Golgi apparatus The Golgi apparatus was discovered by an Italian neurologist, Camillo Golgi in 1873. This apparatus occurs in almost all animal cells except red blood cells. Animal cells usually have a single Golgi apparatus. Some cells have more of Golgi apparatus. In most of the ectodermal and endodermal cells it occurs in between the nucleus and the periphery. In nerve cells it occupies a circum-nuclear position. The simplest unit of the Golgi apparatus is the cisterna. A cisterna is about 1 μm in diameter. It has a membrane bound space. This space accumulates secretions. Numerous such cisternae are associated with each other and appear in a lamellar arrangement. In the lamellar arrangement the space between each cisterna is 20-30 nm. A group of these cisternae is called the dictyosome. A group of dictyosomes constitute the Golgi apparatus. Typically a Golgi apparatus appears as a complex arrangement of interconnecting tubules, vesicles and cisternae. The Golgi apparatus is the site of synthesis of biochemicals. They also collect proteins and lipids made in the ER and add additional substances. Lysosomes These are tiny vesicles surrounded by a membrane. Lysosomes are involved in intracellular digestion and are primarily meant for destroying unwanted and aged organelles inside the cells. Lysosomes were initially named as ‘perinuclear dense bodies’. The name ‘lysosome’ was coined by C.de Duve in 1955. Lysosomes occur in all animal cells. However they are not found in mature mammalian erythrocytes. Muscle cells contain very few lysosomes. They are numerous in epithelial cells of secretory and excretory organs. Each lysosome is a round structure. It is filled with a dense material. Their shapes and Zoology 11101 10 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE densities vary. Their size ranges from 0.2 to 5 μm. Lysosomes originate either from the Golgi apparatus or directly from the endoplasmic reticulum. Lysosomes may contain up to 40 types of hydrolytic enzymes. The enzymes are mostly proteases, nucleases, glycosidases, lipases, phospholipases, phosphatases and sulphatases. The enzymes they contain are used in the dissolution and digestion of redundant structures or damaged macromolecules from within or outside the cell. For example, when an animal cell ingests food into a food vacuole, lysosmes fuse with the vacuole and break down the contents. Their enzymes digest carbohydrates, fat and proteins. When a cell dies its own lysosomes release the enzymes that digest the remains of the cell in a process known as autolysis. The Cytoskeleton The cytoskeleton contains actin filaments (microfilaments), intermediate filaments, and microtubules, which maintain cell shape and allow the cell and its organelles to move. Therefore, the cytoskeleton is often compared to the bones and muscles of an animal. However, the cytoskeleton is dynamic, especially because its protein components can assemble and disassemble as appropriate. Apparently a number of different mechanisms regulate this process, including protein kinases that phosphorylate proteins. 1- Actin filaments are long, extremely thin, flexible fibers (about 7 nm in diameter) that occur in bundles or meshlike networks. Each actin filament contains two chains of globular actin monomers twisted about one another in a helical manner. Actin filaments play a structural role when they form a dense, complex web just under the plasma membrane, to which they are anchored by special proteins. They are also seen in the microvilli that project from intestinal cells, and their presence most likely accounts for the ability of microvilli to alternately shorten and extend into the intestine. 2-Intermediate filaments (8–11 nm in diameter) are intermediate in size between actin filaments and microtubules. They are a ropelike assembly of fibrous polypeptides, but the specific type varies according to the tissue. Some intermediate filaments support the nuclear envelope, whereas others support the plasma membrane and take part in the formation of cell-to- cell junctions. In the skin, intermediate filaments, made of the protein keratin, give great mechanical strength to skin cells. Intermediate filaments are also highly dynamic and will disassemble when phosphate is added by a kinase. There are several types of intermediate filament, each constructed from one or more proteins characteristic of it. keratins are found in epithelial cells and also form hair and nails; nuclear lamins form a meshwork that stabilizes the inner membrane of the nuclear envelope; neurofilaments strengthen the long axons of neurons; vimentins provide mechanical strength to muscle (and other) cells. Despite their chemical diversity, intermediate filaments play similar roles in the cell: providing a supporting framework within the cell. Zoology 11101 11 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE 3-Microtubules  are straight, hollow cylinders whose wall is made up of a ring of 13 "protofilaments";  have a diameter of about 25 nm;  are variable in length but can grow 1000 times as long as they are wide;  are built by the assembly of dimers of alpha tubulin and beta tubulin;  are found in both animal and plant cells. In plant cells, microtubules are created at many sites scattered through the cell. In animal cells, the microtubules originate at the centrosome Microtubules participate in a wide variety of cell activities. Most involve motion. The motion is provided by protein "motors" that use the energy of ATP to move along the microtubule. Centrioles The centrioles are two cylindrical, microtubular structures found near the nucleus. When a centriole supports a flagellum or cilium, it is called the basal body. The centrioles are absent in prokaryotes, red algae, yeast cells and flowering plants and some non-flagellated or non-ciliated protozoans. The centrioles range in size from 0.15-0.25 μm in diameter. In most of the animal cells the centrioles are the focal point for the centrosome. The centrosome organizes cytoplasmic microtubules during interphase in mitosis. It provides the two poles of the mitotic spindle. The centrioles form the basal body and the cilia. In spermatozoon one centriole gives rise to the tail fibre or flagellum. The centrioles are also involved in ciliary and flagellar activity. Zoology 11101 12 Dr. Ahmed M. EL-SABROUT Department: Applied Entomology and Zoology. Class: level one. Subject name & code: Zoology 11101. Dr. Ahmed Mohamed EL-SABROUT FACULTY OF AGRICULTURE Zoology 11101 13 Dr. Ahmed M. EL-SABROUT