Bioscience Note 2023-2024 PDF

Bioscience (Code: GBDS 113) 1st semster – 1st year Dental student Dr/ Ghada Mutawa Lecturer of Bioscience at HUE 2023-2024  ‫جامعة حورس‬-‫رؤية ورسالة كلية طب األسنان‬ ‫جامعة حورس‬-‫ر...

Bioscience (Code: GBDS 113) 1st semster – 1st year Dental student Dr/ Ghada Mutawa Lecturer of Bioscience at HUE 2023-2024  ‫جامعة حورس‬-‫رؤية ورسالة كلية طب األسنان‬ ‫جامعة حورس‬-‫رؤية كلية طب األسنان‬ ‫التميز والريادة في مجال طب األسنان محليا ً وإقليميا ً ودوليا ً من حيث التعليم والبحث العلمي وخدمة‬ ‫المجتمع‬ Vision of the Faculty of Dentistry - Horus University Excellence and leadership in the field of dentistry locally, regionally and internationally in terms of education, scientific research and community service. ‫جامعة حورس‬-‫رسالة كلية طب األسنان‬ ‫إعداد خريجين مؤهلين بالمعرفة النظرية والمهارات العمليه والسلوكيات اإلنسانية التي تمكنهم من‬ ‫المنافسه في سوق العمل ونقل المعرفة من خالل إجراء الدراسات والبحوث العلمية وتقديم الخدمات‬.‫المجتمعيه المتميزه للمواطنين‬ Mission of the Faculty of Dentistry - Horus University Preparing qualified graduates with theoretical knowledge, practical skills and human behaviors that enable them to compete in the labor market and transfer knowledge through conducting studies and scientific research and providing distinguished community services to citizens. ‫عميد الكليه‬ ‫مديروحدة ضمان الجوده‬ ‫ محمد حامد غازي‬/‫د‬.‫ا‬ ‫ ريهام محمد عبد للا‬/‫د‬.‫ا‬ [email protected] ‫وحدة ضمان الجوده‬ 1 Intended Learning Outcomes (ILO's): a- Knowledge and understanding: By the end of this course, the student should be able to: 1. Identify the different types of cell, and describe different types of cell organelles 2. Recognize the different structure between DNA and RNA 3. Describe the cell cycle and steps of different cell divisions. 4. State the different stages of embryogenesis and the pattern of gene expression 5. Recognize blood, different types of blood cells, and steps of haemostasis. 6. Explain the difference between the variable types of dental stem cells. 7. Explain gene mutation and hyflick theory and its relation with cell mortality. b- Intellectual skills: By the end of this course, the student should be able to: 1. Distinguish the variation of genetic materials according to the state of the human cell. 2. Predict the future differentiation of cells 3. Compare between different cellular components of blood and plasma 4. Distinguish the different types of stem cells according to their sources and their ability to differentiate 5. Expect the type of gene mutation from the sequence of the mutant gene c- Professional and practical skills: On the end of this course, the student should be able to: 1. Practice to acquire professional skills in using the light microscope 2. Practice to scan and magnify the Eukaryotic Cell by light microscope 3. Sketch the microscopic embryonic stages 4. Demonstrate the type of blood group, and test the computability of blood transfusion 5. Acquired a professional skill and sensitivity to use the light microscopes for the investigation of different types of blood cells. d- General and transferable skills: On the end of this course, the student should be able to: 1. Develop skills related to creative thinking through self-learning 2. Develop the skills related to oral presentation and scientific research 3. Develop the skills in browsing and reading scientific resources  Content Subject page I- Introduction 1 II- Cell biology 3 III- Genetics 15 IV- Cell Cycle 24 V- Embryonic Development 37 VI- Stem Cells 45 VII- Blood 56 VIII- Gene Mutation 67 IX- Hyflick Theory 73 i  Bioscience I- INTRODUCTION Bioscience: Bioscience is a natural science concerned with the study of life and living organisms, including their growth, structure and function. Sub-disciplines of Bioscience: They are defined by the scale at which organisms are studied and the methods used to study them:  Cell biology: is the study of cell structure and function, whereas the cell is the fundamental unit of life.  Histology: is the study of the microscopic structure of tissues. It is commonly performed by examining cells and tissues under a light microscope or electron microscope.  Anatomy: is the study of large body structures visible to the naked eye, such as the heart, lungs, and kidneys.  Physiology: is the study of the functions and activities of living organs, including all physical and chemical processes.  Genetics: is the study of genes, genetic variation, and heredity in living organisms.  Embryology: the prenatal development of gametes (sex cells), fertilization, and development of embryos and fetuses. 1  Bioscience Structural levels of human body There are many levels of structure in the human body, these levels include (Fig.1): 1. Chemical level: This level is the lowest one. The body is formed of atoms that chemically combine to form molecules. N.B.: The atom is the smallest particle of an element. The word atom means indivisible. 2. Cellular level: The molecules combine to form the cells. N.B.: The cell is the smallest structural and functional unit of the body. 3. Tissue level: The cells of the same structure and function form tissues. 4. Organ level: Tissues of different types form organs. 5. System level: Some organs form a system. 6. Human body: Systems together form the human body. Each of them performs a certain function, required for the health and survival of the human being. Figure (1): Structural levels of human body 2  Cell Biology II- Cell Biology The cell Definition The cell is the structural and functional unit of the body (of all living organisms). Types There are two main types of cells (Fig.2):- 1-Prokaryotic organism: is a single-celled organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle N.B.: Prokaryotic (Gr. pro=before + karyon =nucleus). 2-Eukaryotic organism: is any organism whose cells contain a nucleus and other organelles enclosed within membranes. N.B.: Eukaryotic (eu =good&real + karyon =nucleus). Prokaryotic cell Eukaryotic cell Figure (2): Prokaryotic and Eukaryotic cell Nuclear envelop: Without nuclear envelop With nuclear envelop Example: Found in bacteria Found in all human tissues 3  Cell Biology Different Cells in the Human Body There are about 200 different types of cells in the human body. All human cells are of eukaryotic type. They are derived from a single cell (called zygote), formed because of fertilization of an oocyte by a sperm.  Each cell is specialized to perform a certain function (Fig.3); Ex:-  Muscle cell: It is a long slender cell, containing muscle fibers that aid in contraction and relaxation.  Nerve cell: It is surrounded by nerve processes, which receive and transmit impulses.  Fat cell: It contains large spaces for fat storage.  Epithelial cell: Its shape helps in the protection. It is either is flat, cuboidal or columnar. Figure (3): Different forms of Eukaryotic Cell 4  Cell Biology The Cell Structure The cell is formed of three main structures (Fig.4): A-Nucleus B- Cytoplasm C- Cell membrane Figure (4): Diagram showing Cell Structure A-Cell Membrane (Plasma Membrane) This membrane is the outer limit of the cell. It bounds the cell, separating it from the extra-cellular environment. It acts as a selective barrier that regulates the passage of certain substances into or out of the cell and facilitates the transport of specific molecules. N.B.: It is called plasma membrane because it separates the plasma of the cell from the extracellular fluid. B-Cytoplasm Cytoplasm is a fluid medium (called; cytosol), in which the contents of the cell are suspended. N.B. Cytoplasm (Gr. cyto=cell + plasm= substance or thing formed). 5  Cell Biology - Contents of the cytoplasm: it includes Organelles, Cytoskeleton (including microtubules and microfilaments) & Deposits (including; carbohydrates and lipids). Organelles: These are little organs, each of which performs its own function to maintain the life of the cell. 1- Non-membranous organelles: include free ribosomes, polysomes and centrioles. i. Ribosomes: are small granules, formed of r.RNA and proteins. N.B.: RNA acts as messenger carrying information from the nucleus to the cytoplasm. ii. Polysomes: are collections of ribosomes, held together. Figure (5): Free and attached Ribosomes Functions: Ribosomes are the actual sites of protein synthesis. N.B: The free ribosomes or that found in clusters are concerned with the synthesis of protein that used by the cell itself, while the ribosomes attached to the endoplasmic reticulum are the site of synthesis of protein, exported from the cell to other cells e.g. hormones and enzymes (Fig.5). iii. Centrosome: It is a pair of cylindrical structures, called centrioles. The centrioles are rode-shaped bodies, situated near the nucleus. 6  Cell Biology Function: They play an important role in cell division, forming two centers that produce filaments or microtubules called spindle, initiating cell division. 2- Membranous organelles: i. Endoplasmic Reticulum: It is a network of membranous channels inside the cells, (so it acts as a microcirculatory system for the cell). It is found in 2 types (Fig.6): Figure (6): Rough and Smooth Endoplasmic Reticulum - Rough Endoplasmic Reticulum (RER): appears rough (or granular), due to presence of ribosomes on its surface. - Smooth Endoplasmic Reticulum (SER): appears smooth, (no ribosomes on its surface). Function: is the folding of protein molecules in sacs called cisternae and the transport of synthesized proteins in vesicles to the Golgi apparatus. 7  Cell Biology ii. Mitochondria: are spherical or filamentous granules. It have 2 membranes; outer and inner. The inner membrane extends into the mitochondrion, forming folds, (called; cristae) (Fig.7). Functions: Mitochondria are the power station of the cell, responsible for converting the food ingested by the cell into energy (through burning of food in presence of oxygen).This process is called catabolism. Figure (7): Mitochondria iii. Golgi Apparatus: is a stack of flattened membranous sacs associated with tiny vesicles. It is found near the nucleus (Fig.8). Functions: It receives proteins (sent to it by RER), modifies, packages and releases it to different locations in the cell (e.g. formation of membranes of the cell, formation of lysosomes, etc..). So, it likes the traffic director. Figure (8): Golgi Apparatus 8  Cell Biology iv. Lysosomes: are membrane-limited vesicles that contain digestive (hydrolytic) enzymes. N.B.: Lysosomes (lysis=solution + soma=body) Function: intracellular digestion and removal of wastes. C-Nucleus Nucleus is a double-membrane bound cell organelle which present in eukaryotic cells. The nucleus constitutes most of the genetic material of the cell - the DNA. The nucleus maintains the integrity of the genes which regulate the gene expression, in-turn regulating the activities of the cell. Therefore, the nucleus is known as the control center of the cell. Structure: it includes (Fig.9): 1. Nuclear envelope 2. Chromatin 3. Nucleolus 4. Nuclear matrix (nucleoplasm) Figure (9): the Structure of Nucleus 9  Cell Biology 1- Nuclear Envelope o The nuclear envelope is also known as the nuclear membrane. o It is made up of two membranes the outer membrane and the inner membrane. o The outer membrane of the nucleus is continuous with the membrane of the rough endoplasmic reticulum. o The space between these layers is known as the perinuclear space. o The nuclear envelope encloses the nucleus and separates the genetic material of the cell from the cytoplasm of the cell. o It also serves as a barrier to prevent passage of macro-molecules freely between the nucleoplasm and the cytoplasm 2- Nuclear Pore: (Fig.10) o The nuclear envelope is perforated with numerous pores called nuclear pores. o The nuclear pores are composed of many proteins known as nucleoproteins. o The nuclear pores regulate the passage of the molecules between the nucleus and cytoplasm. o The pores allow the passage of molecules of only about 9nm wide. Figure (10): Nuclear Envelope 01  Cell Biology 3- Chromatin: (Fig.11) o The nucleus of the cell contains majority of the cells genetic material in the form of multiple linear DNA molecules. o These DNA molecules are organized into structures called chromosomes. o The DNA molecules are in complex with a large variety of proteins (histones) which form the chromosome. o In the cell they are organized in a DNA-protein complex known as chromatin. o During cell-division the chromatin forms well-defined chromosomes. o Human cells has nearly 6 feet of DNA, which is divided into 46 individual molecules Figure (11): Chromatin condensation 00  Cell Biology Chromosomes - Somatic cell has diploid number of chromosomes: 46 chromosomes (44 autosomes and 2 sex chromosomes : XX or XY)  Male =44+ XY  Female = 44+ XX - Germ cells (Sperm & ovum): have haploid number of chromosomes: 23 chromosomes  Ovum = only 22+X  Sperm = 22+X or 22+Y Figure (12): Chromosome structure - Each chromosome in the somatic cell has homologous pair; one is paternal chromosome (derived from father) and the other one is maternal (derived from mother). 01  Cell Biology - Each chromosome is formed of 2 identical parallel strands called chromatids. - The 2 chromatids are joined at the center by centromere (Fig.12). - Autosomes are numbered from 1 to 22; while chromosomes number 23 is sex chromosome. Morphology of centromere: It depends on the site of centromere (Fig.13): Figure (13): Different Morphology of chromosomes 1- Metacentric chromosome: Centromere is in the center. 2- Sub-metacentric chromosome: Centromere is closer to one end. 3- Acrocentric chromosome: Centromere is very close to one end. 4- Telocentric chromosome: Centromere is at one end. 03  Cell Biology 3- Nucleolus: o The nucleolus is not surrounded by a membrane, it is a densely stained structure found in the nucleus. o It synthesizes and assembles ribosomes and r RNA. o During cell division, the nucleolus disappears. 4- Nuclear matrix: o It is the component that fills the space between the chromatin and the nucleolus in the nucleus. o It is formed mainly of proteins, ions and metabolites. Functions of the Nucleus 1. It controls the heredity characteristics of an organism. 2. It is responsible for protein synthesis, cell division, growth and differentiation. 3. Stores heredity material in the form of (DNA) strands. 4. It is a site for transcription process in which messenger RNA (m RNA) are produced for protein synthesis. 5. It aids in exchange of DNA and RNA (heredity materials) between the nucleus and the rest of the cell. 6. Nucleolus produces ribosomes and it is known as protein factories. 7. It also regulates the integrity of genes and gene expression. 04  Genetics III- Genetics Genetics: It is study of the human inheritance. Inheritance: It is the passage of hereditary traits from one generation to the other. Alleles: the term used (a) for copies or forms of a gene controlling a certain trait (Fig.8) Figure (14): Allele Some genetic terms (Fig.):- - Genotypes: Genetic makeup (2 alleles) : AA, Aa, aa - Phenotypes: Physical trait: tall, Short, Black hair, Blue eye …. There are 2 possibilities of Phenotypes: Dominant (AA&Aa) or Recessive (aa) - Homozygous  same alleles (pure) : (AA&aa) - Heterozygous  different alleles (hybrid) (Aa) Figure (14): Homozygous and Heterozygous 51  Genetics Nucleic acids: are large biomolecules, essential for all known forms of life. Nucleic acids, which include DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), are made from monomers known as nucleotides. Nucleotide structure: Figure (15): Nucleotide structure Each nucleotide has three components (Fig.15): 1. Sugar called Pentose 2. Phosphate group (H3PO4) 3. Nitrogenous bases: Cytosine (C), Guanine (G), Adenine (A), Thymine (T) and uracil (U). NB: If the sugar is 2-deoxyribose, the nucleic acid is DNA. If the sugar is ribose, the nucleic acid is RNA. RNA has Uracil as a nitrogenous base in instead of Thymine (Fig.16). Figure (16): DNA & RNA 51  Genetics 1- DNA (Deoxyribonucleic acid) DNA is a molecule that carries the genetic instructions used in the growth, development, functioning and reproduction of all known living organisms. -Most DNA molecules consist of two biopolymer strands coiled around each other to form a double helix. The two DNA strands are termed poly deoxyribo-nucleotides chain since they are composed of 2-deoxy- nucleotides (Fig.17). DNA Double Helix Figure (17): DNA Double Helix o Each nucleotide attach to the next one on the same strand by 3' & 5' phosphodiester linkage (Covalent bond) o 2 polymer nucleotide chains are held together by H-bonds between the nitrogenous bases (Base Pairs formation). o Double hydrogen bonds between A &T o Triple hydrogen bonds between C &G to form double helix. 51  Genetics o The two polynucleotide chains run in opposite directions (Fig.18). Figure (18): Bonds between nucleotides on DNA 2- RNA (Ribonucleic acid) - RNA is a polymeric molecule essential in various biological roles in expression of genes. RNA have 3 different types; m.RNA, r.RNA and t.RNA. Each type has specific function. - Monomer of RNA is Ribo- nucleotide, and the polymere of RNA is poly ribo-nucleotides chain. - Uracil is a unique nitrogenous base for RNA. 51  Genetics Gene Expression (Protein Synthesis) Definition: Gene expression is the process by which the genetic materials contained within a gene turned into protein which has a physiological role in human body (Fig.19). Figure (19): Gene Expression Gene: It is a small piece of genetic material written in coding regions on DNA. N.B.: there are coding DNA sequence (CDS) called Exons, and non- coding DNA sequence called Introns (Fig.20). Introns are non-coding sections of a gene, transcribed into the precursor mRNA sequence, but ultimately removed by RNA splicing during the processing to mature m.RNA. 51  Genetics Figure (20): Exons and Introns  The process of gene expression involves two main stages:- 1- Transcription:- - Transcription is the process of protein synthesis that involves copying the genetic information contained within DNA into an m.RNA. - During transcription, certain enzyme called helicase unwinding the DNA strand and allow the enzyme RNA polymerase to transcribe only a single strand of DNA (template strand) (Fig.21). - DNA contains the four nucleotide bases adenine (A), guanine (G), cytosine (C) and thymine (T) which are paired together (A-T and C-G). When RNA polymerase transcribes the DNA into mRNA molecule, adenine pairs with uracil (A-U). - At the end of transcription, mRNA is transported to the cytoplasm for the completion of protein synthesis. Figure (21): Transcription II. Translation:- - Conversion the message (genetic materials) within the nucleotide sequences of mRNA into specific amino acid sequences. The amino 02  Genetics acid sequences are joined together to form a protein. It performs by help of transfer RNA (Fig.22). - Transfer RNA is shaped like a clover leaf with three hairpin loops. It contains an amino acid attachment site on one end and a special section in the middle loop called the anticodon site. - The anticodon recognizes a specific area on mRNA called a codon. A codon consists of three continuous nucleotide bases that code for an amino acid (the monomer of protein) or signal the end of translation. - Transfer RNA along with ribosomes read the mRNA codons and produces a polypeptide chain (the polymer of protein). When a termination codon is reached on the mRNA molecule, the translation process ends. The polypeptide chain undergoes several modifications before becoming a fully functioning protein. Figure (22): Translation 05  Genetics Types of RNA RNA molecules are produced in the nucleus of our cells and can also be found in the cytoplasm. There are three primary types of RNA:- 1- MessengerRNA (m.RNA): Figure (23): Messenger RNA - It plays an important role in the transcription of DNA. - As DNA can't leave nucleus, m.RNA carries a message from DNA into cytoplasm (Ribosome). - It contains codons, each codon consists of 3 nucleotides (Fig.23). 2-Transfer RNA (t.RNA): Figure (24): Transfer RNA 00  Genetics - It plays an important role in the translation portion of protein synthesis. - Its job is to transfer amino acid to polypeptide chain on Ribosome. - It carries amino acid on one end and anti-codon on the other end (Fig.24). 3- Ribosomal RNA (r.RNA) Figure (25): Ribosomal RNA -It is a component of cell organelles called ribosomes. A ribosome consists of 40% ribosomal proteins & 60% r.RNA. -Ribosomes are typically composed of two subunits: a large subunit and a small subunit (Fig.25). -Ribosomal subunits are synthesized in the nucleus by the nucleolus. r.RNA is responsible for creating the peptide bonds between the amino acids in the polypeptide chain. 02  Cell Cycle IV- Cell Cycle Events of cell cycle (Fig.26): Figure (26): Cell Cycle 1- Cell growth (Interphase) 2- Cell division (karyokinesis &Cytokinesis) Interphase This is phase in-between the cell divisions. During this phase, the cell grows and performs all its metabolic activities. Figure (27): Interphase  The nuclear membrane and nucleolus are apparent at this phase, but the chromosomes are not apparent (still chromatin) (Fig.27). 42  Cell Cycle  However, if the cell is going to divide, the chromosomal content (DNA) is duplicated. Therefore, for a short time before beginning of mitosis, the cell contains double dose of genes.  Interphase Includes 3 phases during which cell contents are duplication: 1. G1: First growth phase, growth and duplication of all cellular content except DNA. 2. S: DNA synthesis phase, duplication of genetic materials (DNA). 3. G2: Second growth phase, double check for growth and duplication; and also preparation for division. 42  Cell Cycle CELL DIVISION Definition: It is the process by which the cell reproduces itself (Fig.28). Figure (28): Cell Division Significance of cell division: Tissues produce new cells for the following purposes: 1-Body development and growth: this is associated with increasing the cell number. 2-Tissue repair: replacement of cells that continually lost throughout life. 3-Fertilization: Production of new germ cells (sperms or ova). Types of cell division: 1-Mitosis: This type occurs in the somatic cells. 2-Meiosis: This type occurs in the germ cells. 1- Mitosis This type occurs in the somatic cells, resulting in the formation of 2 daughter cells; each of which contains the same number of chromosomes, as the parent cell. 42  Cell Cycle  Mitosis includes two events; A- Nuclear division (karyokinesis) B- Cytoplasmic division (cytokinesis). A- karyokinesis; include four stages or phases: i- Prophase: Figure (29): Prophase - The chromatin is condensed into chromosomes, each of them is formed of 2 identical (sister) chromatids, connected together by button like body called centromere (Condensation). Mother cell has 46 D-chromosomes. - Centrioles move away from each other toward each pole of the cell, forming a mitotic spindle in-between them, as they move (Fig.29). - The nuclear membrane begins to disappear and the pairs of chromatids are attached randomly to the spindle (prometaphase). 42  Cell Cycle ii- Metaphase: Figure (30): Metaphase - The chromosomes align along the cell equator, being attached to the spindle fibers by the centromeres (Fig.30). iii- Anaphase: Figure (31): Anaphase - The centromeres split, and then the chromatids move to the opposite ends of the cell. - Movements of chromatids are probably due to contraction of the fibers of the spindle (Fig.31). 42  Cell Cycle iv- Telophase: Figure (32): Telophase - The nuclear membrane and nucleus reform again. - At the late stage chromosomes at each end of the cell start to uncoil to form chromatin again (Decondensation); each daughter cell has 46 S-chromosome (Fig.32). B- Cytokinesis Figure (33): Cytokinesis - (Division of cytoplasm) occurs, resulting in formation of two daughter cells (Fig.33). 42  Cell Cycle 2- Meiosis It is a special type of cell division, restricted to germ cells (in ovary or testis) and resulting in the formation of haploid gametes (Sperms and ovum) with half the normal number of chromosomes. It consists of two divisions; meiosis I and meiosis II:- Meiosis I: consists of reduction division, resulting in formation of two cells with haploid number of chromosomes (Fig.34) A- Karyokinesis I; include four stages or phases: i-Prophase I: Figure (34): Prophase I - The chromatin is condensed into chromosomes (Condensation), and mother cell has 46 D-chromosomes (Fig.34). - Each paternal and maternal D- chromosome arrange beside each other to prepare for crossing over. - Crossing over or synapsing is a physical exchange of chromosome parts. crossing-over is the process that can give rise to genetic recombination and produce tetrad chromosomes. The nuclear envelope start to disappear at prometaphase I, allowing the spindle to enter the nucleus. 03  Cell Cycle i-Metaphase I: Figure (34): Metaphase I - The pairs of tetrad D-chromosomes align along the cell equator, being attached to the spindle fibers by the centromeres (Fig.34). ii- AnaphaseI: Figure (35): Anaphase I - The tetrad D-chromosomes split and move to the opposite ends of the cell. - Movements of chromosomes are probably due to contraction of the fibers of the spindle (Fig.35). 03  Cell Cycle iii- Telophase I: Figure (36): Telophase I - The nuclear membrane and nucleus reform again. - At the late stage tetrad D-chromosomes at each end of the cell start to uncoil to form chromatin again (Decondensation); each daughter cell has 23 D-chromosome (Fig.36). B-Cytokinesis I Figure (37): Cytokinesis (Division of cytoplasm) occurs, resulting in formation of two daughter cells; each cell has unique version of genetic materials (Fig.37). 04  Cell Cycle Meiosis II: consists of equal division (like mitotic division), but not proceeded by duplication of chromosomes (interphase II lacks S-phase). B- Karyokinesis II; include four stages or phases: i-Prophase II: Figure (38): Prophase II - The chromatin is condensed into chromosomes (Condensation), and each mother cell has 23 tetrad D-chromosomes (Fig.38). - The nuclear envelope start to disappear at prometaphase II, allowing the spindle to enter the nucleus. i-Metaphase II: Figure (39): Metaphase II - The tetrad D-chromosomes align along the cell equator, being attached to the spindle fibers by the centromeres (Fig.39). 00  Cell Cycle iv- AnaphaseII: Figure (40): Anaphase II - The tetrad D-chromosomes split into 2 tetrad chromatids and move to the opposite ends of the cell due to contraction of the fibers of the spindle (Fig.40). v- TelophaseII: Figure (41): Telophase II - The nuclear membrane and nucleus reform again. - At the late stage tetrad S-chromosomes at each end of the cell start to uncoil to form chromatin again (Decondensation); each daughter cell has 23 S-chromosome (Fig.41). 02  Cell Cycle B-Cytokinesis II Figure (42): Cytokinesis II (Division of cytoplasm) occurs, resulting in formation of four daughter cells; each cell has unique version of genetic materials (Fig.42). - In addition, the daughter cell has a new collection of genetic materials, due to process of crossing over (synapsing) and random distribution of homologous chromosomes at the equator of the dividing cell to produce tetrad chromosomes. This results in specious variations (i.e. each person is different from the other) (Fig.43). Figure (43): Meiotic Cell division 02  Cell Cycle Differences between Mitotic and Meiotic Cell Division The main differences include the following: Mitotic division Meiotic division Site Somatic cells Germ cells (in gonads) Results: Two cells Four cells Number of Diploid 2N Haploid N chromosomes of (46 chromosomes) (23 chromosomes) the daughter cell Important for the Development, growth Fertilization by sperm and occurrence of and tissue repair. ovum. 02  Embryogenesis V-Embryonic Development Definition Embryogenesis is the process of cell division and cellular differentiation of the embryo that occurs during the early stages of development. Human development entails growth from a one celled zygote to an adult human being (Fig.44). Figure (44): Embryogenesis Steps of Embryogenesis A- Fertilization Fertilization takes place when the sperm (Fig.45) has successfully entered the ovum (oocyte) (Fig.46) and genetic material carried by the gametes, fuse together, resulting in the zygote, (a single diploid cell).  This usually takes place in the lateral third of the fallopian tubes. Figure (45): Sperm Figure (46): Ovum (oocyte) 73  Embryogenesis Stages of Fertilization:- Successful fertilization is enabled by 4 processes:- 1. Chemotaxis: Figure (47): Chemotaxis - Chemotaxis (Response to chemical stimulus): is the 1st process which directs the movement of the sperm towards the ovum (Fig.47). 2. Adhesive compatibility: - Adhesive compatibility is the 2nd process of fertilization when sperm adhered to the ovum by its acrosome. 3. Acrosomal reaction: Figure (48): Acrosomal reaction 73  Embryogenesis - Acrosomal reaction takes place when the front part of the sperm head is capped by an acrosome which contains digestive enzymes to break down the zona pellucida and allow its entry. The entry of the sperm causes calcium to be released which blocks entry to other sperm cells. A parallel reaction takes place in the ovum called the zona reaction (Fig.48). 4-Zona Reaction: This sees the release of cortical granules that release enzymes which digest sperm receptor proteins, thus preventing polyspermy. The granules also fuse with the plasma membrane and modify the zona pellucida in such a way as to prevent further sperm entry.  The zygote contains the combined genetic material 46 chromosomes carried by both the male and female gametes which consist of the 23 chromosomes from the nucleus of the ovum and the 23 chromosomes from the nucleus of the sperm. The 46 chromosomes undergo mitotic division which leads to the formation of the embryo having two cells. B- Cleavage - This first division marks the beginning of the cleavage process which continues with the division of the first 2 cells by mitosis to give 4 cells which then divide to give 8 cells and so on. This is quite a slow process taking from 12-24 hours for each division (Fig.49) Figure (49): Cleavage 73  Embryogenesis - The zygote undergoes further cleavage, increasing the number of cells without any increase in the size of the initial zygote. This means that the proportion of nuclear genetic material is greater than that of the cytoplasm in each cell (Fig.50). Figure (50): Compaction - When eight blastomeres have formed they are undifferentiated and aggregated into a sphere, and when the cells number about sixteen or thirty-two the solid sphere of cells is termed a morula. C. Blastulation The process of forming the blastocyst, cleavage itself is the first stage in blastulation ,typically four or five days old and are a hollow microscopic ball of cells called the blastocyst Figure (51): Blastula 04  Embryogenesis The blastocyst includes three structures (Fig.51): - The Trophoblast: which is the layer of cells that inner surrounds the blastocyst. - The blastocoel: this is the hollow cavity inside the blastocyst. - The inner cell mass: approximately 30 cells at one end of the blastocoel. N.B.: The inner cell mass will give rise to the embryo, while the fetal part of the placenta will form from the outer trophoblast layer. D- Gastrulation Figure (52): Gastrula - Gastrulation is a step in the embryonic development, during which the single-layered blastula is reorganized into a trilaminar ("three- layered") structure known as the gastrula. - These three germ layers are known as the ectoderm, mesoderm, and endoderm (Fig.52). 04  Embryogenesis E- Organogenesis Specific layers of embryo give rise to specific organ systems (Fig.53):- - Ectoderm generates the outer layer of the embryo and produces the surface layer (epidermis) of the skin and forms the nerves. - Endoderm becomes the innermost layer of the embryo and produces the digestive tube and its associated organs (including the lungs). - Mesoderm becomes sandwiched between the ectoderm and endoderm and generates the blood, heart, kidney, gonads, bones, and connective tissues. Figure (53): Differentiation 04  Embryogenesis Pattern of Gene Expression - There are 210 different types of cells in human body - Although all cell types have the same genome (DNA sequences) and differentiate from the 1st singled cell (zygote), but each type have different morphology and different function. - This differentiation is related to pattern of gene expression, which mean each type of cells turning genes on and off (Fig.54). Figure (54): Cell Differentiation Ex: - gene that code expressed into protein for the muscle contraction different from the white blood cells. 07  Embryogenesis Turning genes on&off through embryonic development:  Zygote is homogenous with no left &right or up & down  Polarity of zygote depends on the point of sperm entry during fertilization or the environment as: uterine wall. So the zygote has two sides (polar and non-polar).  Polar side have the chemical substances which diffuse through the early embryo , so the cells have different concentrations ( high – medium – low ) of this substance according to the distance from polar side.  Some genes turning on & off according to the concentration of this substances, so the position of this cells in early embryo determine the type of cells. 00  Stem Cells VI- Stem cells Definition: A cell that has the ability to continuously divide and differentiate (develop) into various other kind of cells/tissues. When a stem cell divides, each daughter cell has the potential to either remain a stem cell or become another type of cell with more specialized function such as muscle cell red blood cell or brain cell (Fig.55). Figure (55): Stem Cell Stem cell function : Figure (56): Differentiation of stem cell. Stem cells are the raw material from which all of the body’s mature, differentiated cells are made. Stem cells give rise to brain cells, nerve cells, heart cells, pancreatic cells, etc (Fig.56) 54  Stem Cells Unique properties of Stem Cell (Dynamic cells): - Are undifferentiated “master” cell that do not yet have a specific function. - Can change to one or several different cell types (differentiate) under proper conditions. - Can undergo unlimited cell division and self-renewal (Fig.57) Figure (57): Properties of stem cells Stem cells are unspecialized:  It doesn't have any tissue-specific structures that allow it to perform specialized functions - SCs can't work with its neighbors to pump blood through the body (like a heart muscle cell). - SCs can't carry molecules of oxygen through the bloodstream (like a red blood cell). - SCs can't transport electrochemical signals to other cells that allow the body to move or speak (like a nerve cell). 54  Stem Cells Division of Stem Cells 1- Symmetric division gives us a rise to two identical daughter cells, both have stem cell properties. 2- Asymmetric division produces only one stem cells and a progenitor cell with limited self-renewal potential. Progenitors can differentiate into a mature cell (Fig.58). Figure (58): Types of division of stem cells Main types of Stem Cells: 1- Embryonic Stem Cells (ESCs). 2- Adult Stem Cells (ASCs). 1- Embryonic Stem Cells: Embryonic stem cells created from inner cell mass cells that exist only in very early embryos (blastocyst) and are capable of giving rise to all of the cell types in the body (Fig.59). 54  Stem Cells Figure (59): Embryonic stem cells 2- Adult stem cells:- Are undifferentiated cells, found throughout the body after development, that multiply by cell division to replace dying cells and regenerate damaged tissues. Also they known as somatic stem cells (Fig.60). Figure (60): Adult Stem Cells 54  Stem Cells Examples of Adult stem cells:- 1- Hematopoietic stem cells Hematopoietic stem cells are found mainly in the bone marrow and give rise to all the blood cell types. Hematopoietic stem cells also reside in umbilical cord blood. 2- Mesenchymal stem cells Mesenchymal stem cells (MSCs) are the stromal origin (connective tissue cells of any organ) and may differentiate into a variety of tissues. MSCs reside in bone marrow, placenta and umbilical cord blood. 3- Mammary stem cells Mammary stem cells provide the source of cells for growth of the mammary gland during puberty and gestation and play an important role in carcinogenesis of the breast. 4- Intestinal stem cells Intestinal stem cells divide continuously throughout life and produce the cells lining the surface of the small and large intestines. 5- Endothelial stem cells Endothelial Stem Cells are one of the three types of multipotent stem cells found in the bone marrow. They are a rare group with the ability to differentiate into endothelial cells, the cells that line blood vessels. 6- Olfactory adult stem cells Olfactory adult stem cells have been successfully harvested from the human olfactory mucosa cells, which are found in the lining of the nose and are involved in the sense of smell. 54  Stem Cells 7- Spermatogonial stem cells Spermatogonial progenitor cells found in the human testicles and have ability to produce sperms (the male gamete). Comparison between embryonic and adult stem cells:- Adult stem cells Embryonic stem cells Created from the 3 cell layers Created from inner cell Origin in (gastrula stage), also reside mass cells that exist only in or near their adult tissue. in very early embryos (blastocyst) Multipotent; Oligopotent; Pluripotent stem cells Potentiality unipotent stem cells Are capable of giving rise to Are capable of giving rise Function functional cells in their tissue to all of the cell types in the body Haematopiotic, endothelial Inner cell mass in Examples and mesenchymal stem cells blastocyst 45  Stem Cells Potential types of stem cells: 1- Totipotent stem cell: - these cells have unlimited capabilities for differentiation, as it have ability to form extra embryonic membranes (placenta), and all cell types in embryo. Ex: Morula and zygote. 2- Pluripotent stem cell: - these cells have ability to give rise to all tissues of organism. They are embryonic stem cells Ex: Inner cell mass of blastocyst. 3- Multipotent stem cell: - this cell has ability to give rise to many but not all cell types. Ex: Hematopoietic stem cells. 4- Oligopotent cell :– these cells have ability to give rise to few types of cells; they are more restricted than multipotent. Ex: Lymphoid stem cells. 5- Unipotent cells or monopotent:- these cells have ability to give rise to a single differentiated cell line Ex: spermatogonial stem cells. 45  Stem Cells Dental Stem Cells Figure (61): Dental Stem Cells  There are many examples of Dental Pulp stem cells (Fig.61):- 1- Dental Pulp Stem Cells (DPSCs) 2- Stem Cells from Human Exfoliated Deciduous teeth (SHED) 3- Stem cells from Apical Papilla (SCAP) 4- Periodental ligament Stem Cells (PDLSCs) 5- Gingival Mesenchymal Stem Cells (GMSCs) 1- Dental Pulp Stem Cells (DPSCs):- Figure (62): Dental Pulp Stem Cells 45  Stem Cells - Site: DPSCs are mesenchymal type of stem cells inside dental pulp (Fig.62) - Ability of differentiation: DPSCs can differentiate into odontoblasts, osteoblasts, and chondrocytes - Application: regeneration of pulp and dentine 2- Stem Cells from Human Exfoliated Deciduous teeth (SHED):- Figure (63): SHED - Site: SCs which isolated from the pulp of human exfoliated deciduous teeth (Fig.63). - Ability of Differentiation: SHED have higher potential than DPSCs, because SHED able to differentiate into greater types of cells like: osteoblasts, odontoblasts, adipocytes and neural cells. - Applications: SHED can generate mineralized tissue, which can be used to enhance orofacial bone regeneration. 45  Stem Cells 3- Stem Cells from Apical Papilla (SCAP):- Figure (64): Stem Cells from Apical Papilla - Site: SCAP residing in the tooth root apex (Fig.64) - Ability of Differentiation: odonoblast - Application: Regeneration of Root dentin. 4- Periodontal ligament Stem Cells (PDLSCs):- Figure (65): Periodontal ligament Stem Cells 45  Stem Cells Site: Periodontal ligament (Fig.65) Ability of differentiate: PDLSCs can differentiate Cementum Application: Periodontal tissue repair 5- Gingival Mesenchymal Stem Cells (GMSCs):- Figure (66): Gingival Connective Stem Cells - Site: Gingival connective tissue (Fig.66). - Ability of differentiation: have osteogenic potential. - Application: Bone regeneration in mandibular defects. 44  Hematology Blood Definition: It is a special type of connective tissue, i.e. it is the only fluid tissue in the body. It contains the living blood cells, being suspended in a non-living matrix called plasma. Composition of Blood - It is formed of cells, suspended in plasma:- I. Blood Cells: They represent about 45% of the total volume of blood. They include the following types: 1. Red blood cells "Erythrocytes"; that carry oxygen. 2. White blood cells "Leukocytes"; that fight infection. 3. Blood Platelets or Clotting cells "Thrombocytes"; that help in blood clotting. II. Plasma: - It represents about 55% of the total volume of blood. - It is a clear straw-colored fluid. - It is formed of:  Water (about 90%)  Dissolved substances (about 10%). The dissolved substances include the following: 1. Proteins (about 7%): include; i. Albumin (it keeps the osmotic balance "keeps water inside the blood"), ii. Globulin (for body defenses "antibodies") iii. Fibrinogen iv. Prothrombin. 65  Hematology - The last two proteins are needed for blood clotting. 2. Electrolytes (about 1%), e.g. sodium, potassium, magnesium, calcium... 3. Substances transmitted by the blood, (about 2%). They include; i. Nutrients, e.g. glucose, amino acids, fatty acids and vitamins. ii. Waste products, e.g. urea and uric acid. iii. Hormones; secreted from endocrine glands. iv. Respiratory gases, e.g. oxygen and carbon dioxide.  It is examined by spun of a sample of blood in a centrifuge machine. Three areas appear, as follows: 1. A reddish mass appears at the bottom: formed by the red blood cells "Erythrocytes". It represents about 45% of the total volume. This is called haematocrit value. - Haematocrit value is the percentage of red blood cells in a volume of blood. It is about 45%. 2. A clear straw-coloured fluid appears above: formed by the blood plasma. It represents about 55% of the total volume. 3. A thin whitish layer called "Buffy coat" appears at the junction between the above two regions: The white blood cells "leukocytes" form it. It represents less than 1% of the total volume (Fig. 67). 65  Hematology Figure (67): Centrifugation of Blood sample -Main proprieties of Blood 1- Color of Blood: - It depends on the amount of oxygen, carried by the blood. The color varies from bright red (oxygen-rich) to dark red (oxygen- poor). 2- Viscosity of Blood: - The blood is 5 times more viscous (more thickly) than water. This is mainly depending on: Plasma viscosity (Plasma Proteins) and RBCs Viscosity (Hematocrit value). 3- Volume of Blood: - In the adults, it is about 5 - 6 liters. 65  Hematology - Functions of Blood 1- Transport Functions: o It carries respiratory gases; O2 from the lungs to the tissues and CO2 from the tissues to the lungs for excretion. o It carries nutrients; from the alimentary tract to the liver and then to the tissues of the body. o It carries waste products; resulting from activity of the tissues to the kidneys for excretion. o It carries heat; from the active heat-producing cells to the less active cells, (It distributes the body heat). o It carries the chemical messengers "hormones"; to the target organs and tissues, to regulate their functions (It distributes the body hormones). 2- Protective Functions: o It fight infections; through its contents of plasma proteins (Globulin) and white blood cells. 1- Clotting Functions: It helps to arrest haemorrhage through its contents of blood platelets (thrombocytes) that help in clotting of the blood. Blood Cells They include the following types: 1. Red blood cells "Erythrocytes". 2. White blood cells "Leukocytes". 3. Platelets "Thrombocytes". 65  Hematology 1. Red blood cells "Erythrocytes"  Shape of the cell: They are very minute and numerous, biconcave, non-nucleated disc-shaped bodies (Fig.68).  Size of the cell: It is very minute, having a diameter of about 7 microns (micron = 1/1000 millimeter).  Count of the cells: They are very numerous about 5 million per cubic millimeter of blood.  Contents: They have no nucleus, but contain a special type of complex protein known as haemoglobin. Figure (68): RBCs Haemoglobin:  Composition: - Haemoglobin is a complex protein, formed of a globin (PolyPeptide molecules: α &β chain) and iron-containing substances called haem (Fig.69). It has a great attraction to oxygen, i.e. it combines (carry oxygen) in the lungs (forming oxy-haemoglobin). Haemoglobin is measured in grams per 100 ml (about 15 gm per 100 ml). 56  Hematology Figure (69): Haemoglobin Life span of red blood cells: Red blood cell lives about 120 days, after which it is ingested by cells in the spleen and lymph nodes. Haemoglobin is split into: i. Globin that returns to the protein stores in the body or excreted in urine if the breakdown is increased. ii. Haem that is further split into iron and pigment "bilirubin". The iron is re-used again. The pigment is converted in the liver into bile pigment and excreted in the faeces. 2. White blood cells "Leukocytes" They are the only 'complete cells' in the blood; that they contain nuclei and organelles. 56  Hematology  Size: Their size is larger than that of red blood cells (of about 10 micron in diameter)  Count: but they are less numerous, total leukocytic count; is 4000- 11000/cubic millimeter.  Percentage: less than 1% of the total blood volume.  Functions of leukocytes: Figure (70): Function of WBCs - They represent 'the movable protective army of the body'. They protect the body against damage caused by bacteria, viruses, parasites and tumors. They have a character, not found in red cells; that they can slip out of the blood vessels to areas of inflammation and immune response (Fig.70). 56  Hematology They are classified into 2 main types (Fig.71): 1. Granulocytes (polymorphonuclear leukocytes): They contain granules in their cytoplasm, so they are called granulocytes. In addition, their nuclei show several lobes, so they are called polymorphonuclear (poly=many, morph=form). They are divided into 3 types according to their staining; Neutophils, Eosinophils and Basophils. a. Neutrophils (about 70% of total white blood cells): They do not stain intensely with either dye. They are called phagocytes (phag=eat or swallow) because they are able to ingest and destroy small particles, e.g. bacteria and cell debris. b. Eosinophils: (about 4% of total white blood cells): They stain with a red acidic dye called eosin. They increase in allergy, and thought to engulf substances that trigger the allergies. c. Basophils: (about 1% of total white blood cells): They stain with basic (alkaline) dyes. Their granules contain heparin (anticlotting substance) and histamine (a chemical that is involved in allergic response), so they are associated with the allergic reactions. 2. Agranulocytes: They have clear cytoplasm (without granules) and non-lobed nucleus. They include; monocytes and lymphocytes. a. Monocytes (about 5% of total white blood cells): They are the largest of the white cells. Also, they contain one large horseshow- shaped nucleus, so they also called mononuclear cells. They are phagocytic cells. 56  Hematology b. Lymphocytes (about 20% of total white blood cells): They are formed in the lymphatic tissue and are concerned in production of antibodies. Figure (71): Types of WBCs 3. Platelets "Thrombocytes"  They are small fragments (not actual cells). They appear as darkly stained, small, irregular shaped bodies, in-between the other blood cells. They develop in the bone marrow from a large cell called megakaryocyte that is fragmented into 50 or more anucleated pieces.  They are needed for the process of clotting. 56  Hematology Haemostasis - It is the process by which the blood loss is prevented after an injury. - It includes the following 3 stages that work together (Fig. 72): Figure (72): Haemostasis a. Vascular spasm (vasoconstriction): Vasoconstriction is narrowing of the lumen of the cut blood vessel to slow the blood loss. b. Platelet plug formation: Many platelets reach rapidly to the site of injury and form a temporary seal 'platelet plug' to stop the blood flow. c. Coagulation "Blood clotting": This is a complex process that involves clotting of fibrin around the platelet plug and pulls the edges of the cut together. Normally; blood clots within 3-6 minutes. 56  Hematology 55  Gene Mutation GENE MUTATION  A gene mutation is defined as an alteration in the sequence of nucleotides in DNA.  In gene mutations, the DNA code will have a base (or more( missing, added, or exchanged in a codon.  This change can affect a single nucleotide pair or larger gene segment of a chromosome. Types of Gene Mutation: A- Point Mutation (Substitution Mutation):  Point mutations are the most common type of gene mutation.  Also known as base pair substitution.  Change in a single nucleotide polymorphism (SNP).  Point mutation can be categorized into three types: 1- Silent mutation 2- Missense mutation 3- Nonsense mutation 1- Silent Mutation In a silent mutation, a nucleotide is substituted but the same amino acid is produced anyway. This can occur because multiple codons can code for the same amino acid. For example, AAG and AAA both code for lysine, so if the G is changed to an A, the same amino acid will form and the protein will not be affected. 76  Gene Mutation 2- Missense mutation The missense mutation occurs when one nucleotide is substituted and a different codon is formed. The resulted codon produces a different amino acid in the sequence of amino acids. For example, if a missense substitution changes a codon from AAG to AGG, the amino acid arginine will be produced instead of lysine. 3- Non-Sense Mutation: A nonsense mutation occurs when one nucleotide is substituted and this leads to the formation of a stop codon instead of a codon that code for an amino acid. A stop codon a certain sequence of bases (TAG, TAA, or TGA in DNA, and UAG, UAA, or UGA in RNA) that stops the production of the amino acid chain. 76  Gene Mutation  Way of Substitution Mutation: 1- Transition mutation A transition is the replacement of a base by the other base of the same chemical. 2- Transversion mutation A transversion is the opposite the replacement of a base of one chemical category by a base of the other. 76  Gene Mutation B- Frame shift mutations:  This type of mutation occurs when the addition or loss of DNA bases changes a gene's reading frame. A reading frame consists of 3 bases, each code for one amino acid.  A frame shift mutation shifts the grouping of these bases and changes the code for amino acids.  The resulting protein is usually nonfunctional. There are 2 types of frame shift mutation: 1- Insertion (Adding) Mutation 2- Deletion Mutation 1- Insertion Mutation An insertion changes the number of DNA bases in a gene by adding a nitrogenous base in DNA. As a result, the protein coded by the gene may not function properly. 67  Gene Mutation 2- Deletion A deletion changes the number of DNA bases by removing a nitrogenous base in DNA. Examples of genetic mutation: 1- Dental agenesis (Hypodontia & Oligodontia) Inhertience lack of one or more teeth in humans. a) Hypodontia: 1–6 teeth (excluding molar 3) are missing b) Oligodontia: more than 6 teeth (excluding molar 3) are missing. c) Hyperdontia: Presence of one or more extra teeth that appear in addition to the regular number of teeth. d) Anodontia: the complete absence of teeth (very rare). - Hypodontia: caused by frameshift insertion mutation. A frameshift insertion of 7 basepairs (GCAAGTT) in MSX1 gene - Oligodontia:Frameshift mutation caused by base insertion mutation. 67  Gene Mutation 2- Sickle-Cell Anemia - Hemoglobin is a protein found in red blood cells, and is responsible for the transportation of oxygen through the body. - There are two chains that make up the hemoglobin protein: beta- globins and alpha-globins. - Sickle-cell anemia is caused by a point mutation in the β-globin chain of hemoglobin, causing amino acid glutamic acid to be replaced with the amino acid valine at the sixth position. - A single point mutation in this polypeptide chain of beta globlobin is resulted in the disease known as Sickle Cell Anemia. Sequence for Normal Hemoglobin AUG GUG CAC CUG ACU CCU GAG GAG AAG UCU GCC GUU ACU START Val His Leu Thr Pro Glu Glu Lys Ser Ala Val Thr Sequence for Sickle Cell Hemoglobin AUG GUG CAC CUG ACU CCU GUG GAG AAG UCU GCC GUU ACU START Val His Leu Thr Pro Val Glu Lys Ser Ala Val Thr 67  Hayflick Limit Hayflick Limit Hayflick limit - The Hayflick limit is the number of times a normal human cell will divide before cell division stops. - The normal human cell will divide between 40 and 60 times, So normal cells are not immortal. Explanation: - Before the theory; it was believed that cells had an unlimited potential to replicate. - But Hayflick theory was approved that normal cell has limited capacity of division. - Hayflick theory explains the reason behind the aging of cell populations and appears in the overall physical aging of an organism. - Generally it depends upon the length of a chromosome’s telomeres Telomeres: - Telomeres are repeating DNA sequences found at the ends of chromosomes, which cap the arms of chromosomes. Telomeres provide stability to the chromosome and protect them against DNA loss associated with cell division. - The properties of DNA replication prevent the cells from fully copying the ends of linear DNA (telomeres). Because of the nature of lagging-strand synthesis, DNA polymerase can't completely replicate the 3'end of DNA. 37  Hayflick Limit - Each time a cell undergoes mitosis, the telomeres on the ends of each chromosome shorten slightly. Cell division will stop once telomeres shorten to a critical length. 37  Hayflick Limit Telomerase - Telomerase is an enzyme which is used as a template when it elongates telomeres. - Telomerase is active in stem cells and most cancer cells, but is normally absent in most normal cells. Telomere and telomerase in human stem cells: - Embryonic Stem cells have high levels of telomerase activity during rapid proliferation. - In the developmental stage, telomerase activity gradually decreases in most somatic cells after birth. - In adult stem cells, the level of telomerase activity is low and not sufficient enough to stably maintain their telomere length. So Adult stem cells are considered to be mortal and finally undergo telomere shortening. - Cancer cell might be immortal because it has high activity of telomerase enzyme. 37  Question Bank Question Bank Choose the correct answer: 1- Pattern of gene expression means ……………………. a- Conversion of all genetic materials into proteins b- Conversion of specific genes into proteins c- Turning genes off d- Turning genes on 2- DNA consists of ………………………………………….. a- 2 coiling strands run in opposite direction. b- 2 coiling strands run in the same direction. c- 2 straight strands run in opposite direction. d- 2 straight strands run in the same direction 3- Duplication of genetic materials takes place during ………………….. a- G1&G2-Phases b- G1-phases c- G2-phases d- S-Phase 4- Chromosomes are splitting into chromatids during ………………... a- Anaphase b- Metaphase c- Prophase d- Telophase 76  Question Bank 5- …………………………… differentiate into skin during embryogenesis. a- Ectoderm b- Ectoderm c- Mesoderm d- Trophoblast of blastula 6- The function of free ribosomes is …………………………………... a- Distribution of protein in and outside the cell b- Folding and packing protein c- Production of protein for cell itself d- Production of protein which is exported as hormones and enzymes 7- Daughter cells of meiosis I have …………….. a- 23 – D chromosomes b- 23 – S chromosomes c- 46 – D chromosomes d- 46 – S chromosomes 8- Early embryo after 4th cleavage has ……………………………. a- 16 cells b- 2 cells c- 4 cells d- 8 cells 77  Question Bank 9- Bond links between ribo-nucleotides on RNA single strand is called …..... a- 3,5 phosphodiester bond b- Double and triple hydrogen bond c- Peptide bond d- Triple hydrogen bond 10- Chemotaxis is the 1st stage of fertilization which …….……………. a- Allows sperm entry b- Helps sperm adhering ovum c- Helps sperm reaching lateral third of fallopian tube d- Prevents polyspermy 11- Coding regions on DNA are called ………..…………….. a- Anti-codons b- Codons c- Exons d- Introns 12- ……………….. is the functional part of sperm during chemotaxis. a- Acrosome b- Flagellum (tail) c- Neck d- Nucleus 78  Question Bank 13- ………………... is the power station of the cell. a- Centrioles b- Golgi apparatus c- Lysosome d- Mitochondria 14- ……………. is considered as prokaryotic cell. a- Bacterial cell b- Fat cell c- Muscle cell d- Nerve cell 15- ……………… has genetic material in form of chromatin. a- Anaphase b- Interphase c- Metaphase d- Prophase 16- ………………… is considered as non-membranous organelle. a- Centrioles b- Mitochondria c- Golgi apparatus d- Endoplasmic reticulum 79  Question Bank 17- ………………….. is embryonic stage which has 16-32 cells. a- Blastula b- Gastrula c- Morula d- Zygote 18- Trophoblast produces ……………………. during embryogenesis. a- Lung b- Nerves c- Placenta d- Skin 19- In fertilization; Acrosome digests zona pellucida during ………… a- Acrosomal reaction b- Adhesive compatibility c- Chemotaxis d- Zona reaction 20- ………………. is considered as homozygous dominant genotype. a- AA b- Aa c- aa d- Tall 80  Question Bank True or false: 1- Blastula has inner cavity called blastocoel. ( ) 2- Pentose is sugar of RNA, but 2-deoxy ribose is the sugar of DNA. ( ) 3- Adhesive computability in fertilization means the movement of sperm toward ovum. ( ) 4- The last stage of meiosis and mitosis is cytokinesis ( ) 5- During G1-phase; cell has duplicated DNA. ( ) 6- Zona pellucida is modified at the last stage of fertilization to prevent polysperm. ( ) 7- G and C linked together by triple hydrogen bond, but adenine and thymine linked together by double hydrogen bond. ( ) 8- Blastula consists of tri-laminar layers of ectoderm, endoderm and mesoderm. ( ) 9- Ovum and sperm have haploid number of chromosomes, but zygote has diploid number of chromosomes. ( ) 10- Compaction occurs during cleavage when proportion of cytoplasm becomes greater than the proportion of genetic material. ( ) 11- Introns is non-coding regions on t.RNA ( ) 81  Question Bank 12- Crossing over the genetic materials between paternal and maternal D- chromosomes takes place during mitosis II. ( ) 13- Poly peptide chain is the polymer of protein, and poly nucleotides chain is the polymer of DNA. ( ) 14- Embryogenesis is process of cell division and cellular differentiation which occurs during early stages of development. ( ) 15- Lymphoid stem cells is considered as oligopotent stem cells, but spermatogonial stem cells is unipotent stem cells. ( ) 16- Sperm receptor protein is digested during zona reaction of fertilization ( ) 17- Cells differentiate according to its position in early embryo. ( ) 18- Nucleolus is non-membranous structure which disappears during cell division. ( ) 19- Telocentric is the morphology of chromosomes which has centromere at the center of chromosome ( ) 20- Nuclear envelope disappears completely at metaphase ( ) 82  Question Bank Compare between the following:- 1- Embryonic stem cells Adult stem cells Function Potentialities Example 2- Transcription Translation Role in gene expression Site of process 83  Question Bank 1- Acrosomal Reaction Zona Reaction Number of the step in fertilization Function A) Eukaryotic cell Prokaryotic cell Definition Example 84  Question Bank B) Nucleotide in DNA Nucleotide in RNA Sugar (with drawing) Nitrogenous bases Meiosis I Meiosis II Anaphase (only drawing) Number of daughter cells &chromosomes 85  Question Bank Erythrocytes (RBCs) Leukocytes (WBCs) Number/mm3 Size (μ) Function Prokaryotic Eukaryotic Nucleus Example Basophils Neutrophils Type (category of WBCs) Function Percentage (%) 86  References 1) Iain Brassington & Bloomsbury Academic (2013); Bioscience and the Good Life. 2) Paul Doerder, et al. (2013); General Biology 3) Fikrettin Sahin (2016); Dental stem cells 4) Elliot Berman (2015); The Stem Cell Revolution.