Cell division

Cell division

1. ·

   • G1 - biosynthesis - proteins made, organelles replicate
   • S - synthesis of new DNA - replication of chromosomes
   • G2 - growth - enlargement of developing cell
   • M - nuclear division - mitosis and cytokinesis - cleavage of cytoplasm

2. Mitosis

   • Need for mitosis
     • Asexual reproduction
     • Growth
     • Repair
       • identical - same function
     • Replacement
       • e.g. RBCs and skin cells
   • Prophase
     • chromosomes supercoil (shorten and thicken)
       • consist of pair of sister chromatids
     • nuclear envelope breaks down and disappears
     • centriole divides into 2
     • each daughter centriole moves to poles to form the spindle
   • Metaphase
     • chromosomes move to the equator
     • each chromosome attaches to a spindle thread by its centromere
   • Anaphase
     • centrome splits
       • sister chromatids separate from each other
         • each becomes an individual chromosome
     • spindle fibres shorten
       • chromatids pulled to opposite poles
         • V shaped appearance as centromere leads
   • Telophase
     • chromosomes reach poles
       • New nuclear envelope forms around each set
     • spindle breaks down and disappears
     • chromosomes uncoil
   • Cytokinesis
     • cells splits into 2 identical daughter cells
   • Budding in yeast
     • asexual reproduction
     • bud forms at surface
       • cell undergoes interphase and mitosis
         • budding cell contains a nucleus that has an identical copy of parent cell's DNA
           • bud separates off

3. Meiosis

   • produces gametes in gonads (sex organs)
   • homologous chromosomes have same genes but different alleles
   • one chromosome from each pair goes to daughter cell
   • daughter cells are haploid (23 chromosomes in humans)
   • daughter cells are not genetically identical to parent cells or from each other