Mitosis and Cell Cycle - L1 Notes PDF

Cell Division  normal development health cell death mitosis cell division - where 2 identical daughter cells are formed apoptosis - programmed cell death  The cell cycle period of growth & division of somatic cells G1 = 1o growth phase S = DNA synth...

Cell Division  normal development health cell death mitosis cell division - where 2 identical daughter cells are formed apoptosis - programmed cell death  The cell cycle period of growth & division of somatic cells G1 = 1o growth phase S = DNA synthesis (replication) G2 = preparation for cell division M = mitosis C = Cytokinesis  Cell Division in Eukaryotes Nucleus Genome – Large and complex – DNA contained in linear chromosomes Chromosome number varies between species Chromosomes in different species Man 46 Gorilla 48 Mouse 40 Maize 10 Garden pea 14 Drosophila 8 E.coli 1 Human Chromosomes  Homologous Chromosomes and Sister Chromatids Homologous chromosomes = pair of the same chromosome One chromosome homologue composed of two sister chromatids Chromatids held together by a centromere  Chromosome make up Chromatin: 40% DNA, 60% protein DNA double helix coils around histone proteins, complex = nucleosome Chromatin fibre coiled within supercoil Heterochromatin- condensed, no gene expression Euchromatin- uncoils, gene expression A human metaphase spread  Number of chromosomes/cell Somatic cell -diploid (2n= 46 chromosomes) – Two homologues for each chromosome – One mat. and one pat. chromosome Gametes- haploid (n= 23 chromosomes) – Single copy of each chromosome – One mat. or one pat. chromosome  Cell division in SOMATIC cells *** Prophase Metaphase MITOSIS Anaphase Telophase Cytokinesis (IPMATC) Prophase: Formation of the mitotic spindle apparatus Metaphase Anaphase Telophase and Cytokinesis  Cytokinesis (animal cells) Cleavage furrow - sea urchin Two daughter cells still joined by thin band of cytoplasm Cell Growth Checkpoint  Cell cycle control How often to divide? Too little: an injury may go unrepaired Too much: abnormal growths develop groups of interacting proteins, CHECKPOINTS provide “control”  The Three Checkpoints: *** Check 1: Cell growth at G1 Check 2: Success of DNA replication at G2 Check 3: Mitosis at M  Key concepts cell cycle is co-ordinated to meet the needs of the cell Mitosis = cell division in somatic cells [PMAT] PMAT - prophase,metaphase, anaphase, telophase separation/disjoining of CHROMATIDS daughter cells identical to parent (2n) 2n “checkpoint” checkpoint regulation of cell cycle