Cell Division Chapter IV PDF

Chapter IV. Cell Division and Cell Transport ALTHEA JOMARI G. LAGAZO, M.Sc. and ALVIN G. DOMINGO, M.Sc. Faculty Department of Biological Sciences College of Arts and Sciences OUTLINE OF THE DISCUSSION Chapter IV. Cell Division and Cell Tran...

Chapter IV. Cell Division and Cell Transport ALTHEA JOMARI G. LAGAZO, M.Sc. and ALVIN G. DOMINGO, M.Sc. Faculty Department of Biological Sciences College of Arts and Sciences OUTLINE OF THE DISCUSSION Chapter IV. Cell Division and Cell Transport 1. Cell division a. Period of Interphase b. Mitosis c. Meiosis 2. Cell transport d. Active Transport e. Passive Transport Cell Division 1. Cell Cycle 2. Cell Division a. Period of Interphase b. Mitosis c. Meiosis  WHY DO CELLS DIVIDE??? To reproduce. To grow bigger. To repair injuries. To become more efficient. Cell Cycle Chromosome-Chromatin-DNA Helix Chromatin is a mass of genetic material composed of DNA and proteins which are found in the interphase of the cell cycle. When a cell starts to divide, the tangled mass of chromatin condense into long threads and finally rod-like bodies called chromosomes. Chromatids are the individual chromosomes but in a pair joined to the other copy by a centromere. Chromosomes are composed of DNA tightly-wound around histones. Chromosome-Chromatin-DNA Helix 1. Chromosomes: o “colored body” o seen only when the cell divides o contain genetic info in the form of DNA o are coiled chromatin 2. Composition of Chromatin o Make up chromosomes o Composed of DNA and protein called histones (helps to condense the DNA) o DNA in a chromosome is 10,000x longer than the chromosome itself o Nucleosome: DNA coiled around histones (“ball with string”) o Nucleosomes coil into supercoils – then into chromosomes o Must condense in order to separate correctly during mitosis Chromosome-Chromatin-DNA Helix 3. Chromosome Structure o Can only see chromosomes during division o Each chromosome replicates and is paired as sister chromatids joined at a centromere o Human cell = 46 chromosomes (2n) 1. “n” number = 23 = “haploid” 2. 2n = 46 = “diploid” 3. 4n = 92 (during interphase) 4. Body cells (aka somatic cells) = 2n = 46 MITOSIS 5. Sex cells (aka eggs & sperm) = n = 23 MEIOSIS Cell Cycle CELL CYCLE series of events involving cell growth and cell division that produces two new daughter cells represents all phases in the life of a cell Cell Cycle CELL CYCLE 3 Parts o Interphase o Mitosis (PMAT) - few minutes to several days o Cytokinesis Cell Cycle 1. Interphase More than 90% of the life of a cell is spent in this phase G1: cell growth, development, and protein production (longest) S: “Synthesis”, DNA replication G2: Organelles replicated (shortest) Note: DNA exists as chromatin (no chromosomes yet) Cell Cycle - Interphase G1 Phase/Post Mitotic/Pre-DNA Synthetic Phase/Gap Ist In which following events take place Intensive cellular synthesis. a. Synthesis of rRNA, mRNA ribosomes and proteins. b. Metabolic rate is high. c. Cells become differentiated. d. Synthesis of enzymes and ATP storage. e. Cell size increases. f. Decision for a division in a cell occurs. g. Substances of G stimulates the onset of next S – phase. h. Synthesis of NHC protein, carbohydrates, proteins, lipids. i. Longest and most variable phase. j. Synthesis of enzyme, amino acids, nucleotides etc. but there is no change in DNA amount. Cell Cycle - Interphase S-phase/Synthetic Phase a. DNA replicates and its amount becomes double (2C - 4C). b. Synthesis of histone proteins. c. Euchromatin replicates earlier than heterochromatin. d. Synthesis of NHC (non-histone chromosomal proteins). e. Each chromosome has 2 chromatids. Cell Cycle - Interphase G2-Phase/Pre Mitotic/Post Synthetic Phase a. Intensive cellular synthesis b. Increase in energy store c. Mitotic spindle protein (tubulin) synthesis begins. d. Chromosome condensation factor appears. e. Synthesis of 3 types of RNA and NHC proteins. f. Synthesis of ATP molecule and storage. g. Duplication of mitochondria, plastids and other cellular macromolecular complements. h. Damaged DNA repair occur. Cell Cycle - Mitotic Phase 2. M-Phase/Dividing Phase/Mitotic Phase a. M –phase is the final phase of cell cycle. b. It represents the phase of actual division. c. Prior to it, the cell components have undergone duplication. d. M – phase is, therefore, the stage of separation of already duplicated components. e. It consists of karyokinesis (division of nucleus) and cytokinesis (division of cell protoplast.). Cell Cycle - G0 Phase G0 – Phase (Quiescent Stage) a. Cells are not actively dividing b. The cells remain metabolically active. c. They do not grow or differentiate unless called to do so Three G0 states: 1. Quiescence 2. Senescence 3. Differentiation Cell Cycle - G0 Phase G0 – Phase (Quiescent Stage) Three G0 states: 1. Quiescence a reversible state occurs due to lack of nutrition and growth factors 2. Senescence irreversible state occurs due to ageing and serious DNA damages 3. Differentiation irreversible state is the process in which a stem cell changes from one type to a differentiated one. Cell Division Cell Division Human cell = 46 chromosomes (2n) 1. “n” number = 23 = “haploid” 2. 2n = 46 = “diploid” 3. 4n = 92 (during interphase) 4. Body cells (aka somatic cells) = 2n = 46 MITOSIS 5. Sex cells (aka eggs & sperm) = n = 23 MEIOSIS Cell Division - Mitotic Phase MITOSIS Division of somatic cells (non-reproductive cells) in eukaryotic organisms. A single cell divides into two identical daughter cells. Daughter cells have same # of chromosomes as does parent cell. Cell Division - Mitotic Phase MITOSIS 4 Sub-phases 1st – Prophase 2nd – Metaphase 3rd – Anaphase 4th – Telophase followed by Cytokinesis Cell Division - Mitotic Phase Prophase 3 Major Events 1. chromosomes condense 2. spindle fibers form (spindle fibers are specialized microtubules radiating out from centrioles) 3. chromosomes are captured by spindle Cell Division - Mitotic Phase Prophase 3 Major Events condensing chromati nucleu n chromosome s nucleolu s s centriole s Cell Division - Mitotic Phase Prophase Animal cell Plant cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Cell Division - Mitotic Phase Metaphase - (organizational phase) chromosomes align along equator of the cell, with one kinetochore facing each pole centrioles chromosomes spindle fibers Cell Division - Mitotic Phase Metaphase - (organizational phase) Animal cell Plant cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Cell Division - Mitotic Phase Anaphase (separation phase) sister chromatids separate spindle fibers attached to kinetochores shorten and pull chromatids towards the poles. free spindle fibers lengthen and push poles of cell apart Cell Division - Mitotic Phase Anaphase (separation phase) Animal cell Plant cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Cell Division - Mitotic Phase Telophase spindle fibers disintegrate nuclear envelopes form around both groups of chromosomes chromosomes revert to their extended state cytokinesis occurs, enclosing each daughter nucleus into a separate cell Cell Division - Mitotic Phase Telophase Animal cell Plant cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm Cell Division - Cytokinesis Cytokinesis the cytoplasm of a single eukaryotic cell divides into two daughter cells The actual splitting of the daughter cells into two separate cells occurs differently in both plant and animal cells Cell Division - Cytokinesis Cytokinesis Plant cells undergo cytokinesis by forming a cell plate between the two daughter nuclei. Animal cells undergo cytokinesis through the formation of a cleavage furrow. A ring of microtubules contract, pinching the cell in half. Cell Division - Cytokinesis Cytokinesis Cell Division Cell Division MITOSIS Photomicrograph of mitotic division of a Plant Cell Prophase Metaphase Anaphase Telophase Cell Division REMEMBER! Interphase Prophase Metaphase IPMATC Anaphase Telophase Cytokinesis I Pray More At The Church Julie Camp’s mitosis power point - http://sciencespot.net/Pages/classbio.html#Anchor-mitosis Cell Division Stages of Mitosis Meiosis “Meiosis is the type of cell division that results in four daughter cells, each with half the number of chromosomes of the parent cell.” Meiosis A process where a single cell divides twice Forms four haploid daughter cells Cells produced are gametes: Sperms in males Eggs in females Meiosis has 2 stages: First stage (Meiosis I) Second stage (Meiosis II) Each stage consists of several phases. Meiosis I : Reductional Cell Division Purpose: Sexual reproduction through fusion of male (sperm) and female (egg) gametes Gametes are haploid: Contain half the number of chromosomes compared to other body cells Meiosis results in the formation of haploid cells. Mitosis VS Meiosis 1.It occurs in two stages of the nuclear and cellular division as Meiosis I and Meiosis II. DNA replication occurs, however, only once. 2.It involves the pairing of homologous chromosomes and recombination between them. 3.Four haploid daughter cells are produced at the end, unlike two diploid daughter cells in mitosis. Phases of Meiosis I Meiosis 1 Prophase 1 Prophase I is longer than the mitotic prophase and is further subdivided into 5 substages, leptotene zygotene pachytene diplotene diakinesis Phases of Meiosis I Meiosis 1 Prophase 1 Leptotene - The chromosomes begin to condense and attain a compact structure Zygotene - Initiateshomologous chromosome pairing - Process: Chromosomal synapsis - Accompanied by: Formation of synaptonemal complex - Result: Pair of synapsed homologous chromosomes - Forms: Bivalent or tetrad complex Phases of Meiosis I Meiosis 1 Prophase 1 Pachytene - Key Event: Crossing over of non-sister chromatids - Occurs between: Homologous chromosomes - Location: Recombination nodules - Result: Chromosomes remain linked at crossover sites Diplotene - Key Event: Dissolution of the synaptonemal complex - Result: Separation of homologous chromosomes in bivalents - Exception: Chromosomes remain connected at crossover sites - X-shaped structures formed during separation: Chiasmata Phases of Meiosis I Meiosis 1 Prophase 1 Diakinesis -Key Events: Termination of chiasmata Assembly of the meiotic spindle -Purpose: Separate homologous chromosomes -Additional Changes: Nucleolus disappears Nuclear envelope breaks down Phases of Meiosis I Meiosis 1 Metaphase 1 The bivalents align at the equatorial plate and microtubules from the opposite poles attach to the pairs of homologous chromosomes. Phases of Meiosis I Meiosis 1 Anaphase 1 The two chromosomes of each bivalent separate and move to the opposite ends of the cells. The sister chromatids are attached to each other. Phases of Meiosis I Meiosis 1 Telophase 1 The nuclear membrane reappe ars and is followed by cytokinesis. This gives rise to a dyad of cells. Phases of Meiosis I Stages of Meiosis II Prophase II It immediately sets off after the cytokinesis when the daughter cells are formed. The chromosomes begin to condense accompanied by the dissolution of the nuclear membrane and the disappearance of the Golgi apparatus and ER complex. Stages of Meiosis II Metaphase II The chromosomes are connected to the centriole poles at the kinetochores of sister chromatids through the microtubules. They also get aligned at the equator to form the metaphase plate. Stages of Meiosis II Anaphase II In this phase of meiosis II, there is a simultaneous splitting of the centromere of each chromosome and the sister chromatids are pulled away towards the opposite poles. As the chromatids move towards the poles, the kinetochore is at the leading edge with the chromosomal arms trailing. Stages of Meiosis II Anaphase II The chromosomes dissolve again into an undifferentiated lump and a nuclear envelope develops around it. Followed by cytokinesis, telophase II marks the end of meiosis. Four haploid daughter cells are formed as a result. Significance of Meiosis Animal Reproduction: Occurs through fusion of gametes Gametes fuse to form a zygote Zygote contains genetic material from both parents Significance of Meiosis Meiosis as a Solution: Meiosis reduces the number of chromosomes in gametes Half the number of parent germ cells Prophase I of meiosis allows recombination of homologous chromosomes Importance of Recombination: Recombination introduces genetic variation Key to evolution through sexual reproduction References Miller S.A. and Tupper, T.A. 2019. Zoology. McGraw-Hill. New York. Samberg, E. 2018.Vertebrate Zoology.Syrawood Publishing House. New York, NY Prasad, S.N and Kashyap.2011. A Textbook of th Veterbrate Zoology. 14 Ed. New Age Publishers. New Delhi