Cell Division Chapter 4 PDF

CHAPTER 4: CELL DIVISION  mitosis and meiosis Introduction Cell division – new cells arise from pre-existing cells. Parent cells divide equally into two cells daughter cells Responsible for: importance of cell division i) growth...

CHAPTER 4: CELL DIVISION  mitosis and meiosis Introduction Cell division – new cells arise from pre-existing cells. Parent cells divide equally into two cells daughter cells Responsible for: importance of cell division i) growth of organism ii) replacement of old cells iii) repair of damaged cells and tissues iv) reproduction ex binary fission  Haploid & Diploid cells girl XX boy XY Haploid all 23 chromosomes are not the same  One set of chromosomes  Half the number of chromosomes (n)  In humans, number (n) = 23 must be haploid to avoid uncontrollable  Gametes (sex cells- sperm & ova) cell division carry out mitosis and divide producing identical daughter cell is not identical cuz different genes and penetrate into womb characteristics are same ex; hair colour Diploid zygote after sperm n ovum fertilising same size and same shape= homologous chromosome  Two sets of chromosomes  Chromosomes present in pairs (2n)  In humans, 2n = 46  All body cells (somatic cell) meiosis reduces the cell division meaning to maintain chromosome number  Karyokinesis (nuclear division) - division of the genetic material / chromosomes - each daughter cell receive exactly one complete In eukaryotes involves set, ideally accurate and identical copies Cytokinesis (cytoplasm division) - division of cytoplasm of the parent cell. - each daughter cell receives about half the cytoplasmic content  Karyokinesis Mitosis (equation division) Meiosis (reductional division)  Cell Cycle The recurring sequence of events that includes the duplication of a cell's contents and its subsequent division. DNA MULTIPLICATION In single-cell organisms, each round of the cell cycle produce an entirely new organism. In humans and other higher-order animals, cell death and growth are constant processes replace damage n dead cells cell cycle is necessary for maintaining appropriate cellular conditions.  The cell cycle has a number of universal trends: 1. DNA packaged into chromosomes must be replicated. 2. The copied contents 2 cells formed of the cell must migrate to opposite ends of the cell. 3. The cell must physically split into two separate cells. interphase Two major phases of cell cycle Division phase: Interphase: resting age true or false its false cuz its M phase G1 (Growth 1 / Gap 1) Cytoplasmic phase S (Synthesis) metabolically active G2 (Growth 2 / Gap 2) past year question  Interphase A period of intense synthesis and growth in the cell Cell produces many materials required for its own growth and activities Genetic material DNA replicates during interphase. Division phase Process of nuclear division, which involves separation of chromatids and their redistribution as chromosomes into daughter cells. Cytokinesis occurs after completion of nuclear division. sister chromatids need to preapare materials n things for S phase Gap 1 phase Cell grows in preparation for DNA replication, and certain intracellular components, such as the centrosomes undergo replication. Protein and RNA are synthesized Normal metabolic activities take place Longest phase. 46 chromosomes = 92 chromatids they are identical so its sister chromatids Synthesis phase DNA packaged into chromosomes is replicated/ DNA duplicated/ synthesized To allows each cell created by cell division to have the same genetic make-up. Synthesis of a number of proteins and enzymes that are involved in DNA synthesis. Chromosomes remain extended/ Each chromosome 2 chromatids joined at the centromere Gap 2 phase Mitochondria and chloroplast replicate, tubulin is synthesized. Chromosomes prepare to condense. Centrioles already replicated. Asters are formed Increase energy because its preparing for important phase which is mitosis M phase Nuclear division Cytoplasmic division M phase starts at the end of G2 and ends at the start of the next G1 phase. It includes the four stages of nuclear division (mitosis), as well as cytoplasmic division (cytokinesis).  Mitosis Process where a successive nuclear division 2n 2n in a diploid cell occurs. 2n 2 diploid cells form. 2n 2n Occurs in all body cells except gamete. Ensures that the next generation will have 2n 2n the same number of chromosomes (DNA) 2n and genetically identical to the parent cell. Mitosis Pak MAT - Prophase - Metaphase - Anaphase Two daughter cells are formed. - Telophase Genetically Identical. http://www.johnkyrk.com/mitosis.html Interphase Preparing phase Nucleoli visible Nuclear envelope intact Chromosomes still long and thin, not visible inside the nucleus Centrosome replicate two pairs of centrioles Prophase thin thread like Chromatin condense and become visible in the light microscope. Nucleolus and nuclear membrane disappears. Centrioles moving to opposite ends of the cell. Spindle fibers attach to kinetochore of centromere. Kinetochore The vertebrate kinetochore is a complex structure that specifies the attachments between the chromosomes and microtubules of the spindle and is thus essential for accurate chromosome segregation. it will be holding so tightly until spindle fibre shorten ex u pull someone until their hands becomes two Metaphase Spindle fibers align the chromosomes along the middle of the cell Spindle fiber (metaphase plate) equatorial plane To ensure that when the chromosomes are separated, each new nucleus will receive one copy of each chromosome fishing fish mouth is kinotechore we pull the fish towards u the rod wire becomes short- Anaphase Chromosomes separate. Chromatids move to opposite sides of the cell. not shortening Pulled by depolymerization of the microtubules. spindle fibre Leads by centromeres  prophase and telophase are oppsites only Cleavage furrow Telophase decondense Chromosomes arrive at opposite poles of cell. Nuclear membranes and nucleoli appear. Chromosomes disperse, no cytokinesis longer visible under the light microscope. Spindle fibers disperse Cytokinesis begin.  1]actin formed at the center of the cell 2]actin contract 3]pinches off cytoplasm 4]form two daugher cells 5]forms cleavage furrow Cleavage of an animal cell (SEM) Cytokinesis (animal) In animal cells, cytokinesis results when a fiber ring composed of a protein called actin around the center of the cell contracts pinching the cell into two daughter cells. cleavage furrow 1]vesicles accumulates at equator 2] vesicles pulls together to form larger vesicles 3] cellulose in the cell forms cell wall 4] cell plate is formed Cytokinesis (plant) In plant cells, a cell plate of cellulose forms in the vicinity of the equators and divides the cell into two daughters. golgi apparatus form new cell plate  Differences between mitosis in plant and animal cells Characteristic Animal cells Plant cells Formation of spindle Formation of spindle Formation of spindle fibres fibres between 2 pairs fibres in the absence of of centrioles centrioles Aster formation Present Absent Cytokinesis Involves furrowing & Involves formation of cleavage of cytoplasm cell plate Where it occurs In tissue throughout the Mainly in meristem body tissues  importance Significance of Mitosis Growth Cell replacement Allows genetic stability within the populations of cells (daughter cells formed are genetically identical to their parent cell, no variation) binary fission Basis of asexual reproduction Repair and regeneration  mitosis meiosis meiosis II 2n=4 Process where two successive nuclear division in a diploid cell occurs. 4 haploid cells form. meiosis reduces the number of chromosomes 2n n occurs in reproductive cells (gametes). Meiosis ensures that the next generation will have: - diploid number of chromosomes - combination of traits that differs from the parent (variation).  daughter cells which are haploid Meiosis I Meiosis II 4 daughter cells which are haploid cells Prophase I Prophase II mid sem Metaphase II Leptotene Anaphase II Zygotene Telophase II Pachytene Diplotene Diakinesis Metaphase I Anaphase I Telophase I Two daughter cells are formed 2nn - Chromosome undergoes replication, making an identical copy of itself. - Chromosomes are still long and thin, not visible inside the nucleus. - Cells spend most of their life in this non-reproductive phase.  chromatin condenses chromosomes. - pairing of homologous a pair of chromosomes that have the same shape,size chromosomes. and centromeres are at middle - crossing over occur (*chiasmata). - nuclear membrane and nucleolus disappear. nuclear spindle develops. chromosomes arrange equator of the spindle Meiosis I Five different substages in prophase 1  homologous chromosomes are alligned at the equatorial plate tetrads line-up along the equator of the spindle (equatorial plate). - spindle fibers attach to the centromere region of each homologous chromosome pair. Meiosis I tetrads separate, pulled by microtubules - move to opposite poles of the cell.  chromosomes form a compact group at each pole. - two daughter nuclei haploid (n) chromosomes. - nuclear membrane reforms - nucleolus reappears. Meiosis I Meiosis II: Chromosomes condense again, following a brief interphase (no DNA replication) centrioles replicate. nucleolus and nuclear envelopes (if formed during Telophase I) dissolve. - spindle fibers reform Meiosis II - spindles moving chromosomes into equatorial area Meiosis II centromeres split. chromatids of the chromosomes separate pulled to the opposite poles.  S PHASE - DNA REPLICATION - chromosomes gather into nuclei. - cytokinesis separate the cells - nuclear membrane and nucleolus reappear. - daughter cell n NO DNA REPLICATION Meiosis II  Meiosis I Prophase I Metaphase I Anaphase I Telophase I Prophase II Metaphase II Anaphase II Telophase II Meiosis II  Produce gametes for sexual reproduction Maintain diploid chromosome number across generations. Increase genetic variation when male and female gametes fuse together