Notes

homologous chromosomes
- identical in size
-same banding pattern
-same centromere location
-same gene loci ( location of alleles)
- different alleles
Interphase - G1,S,G2
G1 - cell stores energy, manufactures proteins and synthesize cytoplasmic organelles
S - non-dividing stage, DNA content replicates ( has sister chromatids)
G2 - growth phase, G1« cells continue to build up and store energy, manufacture protein, and cytoplasmic organelles
-duplication of centromere
M- pmat
prophase
chromatin threads tightly coil } 2 sis chromatids and 1 centromere
has a kinetochore, protein attached at centromere
mircotubles elongate via polymerisation of tubulin dimmers to form spindle fibres
centrioles move to opp ends

metaphase
kinetochore spindle fibres attaches to kinetochore of chromosomes. non-kinetochore spindle fibres interact with those of opp poles
randomly aligned on the metaphase plate

anaphase
cohesin which held sis chromatids now cleaves by enzyme separase
centromere divides > separate chromosomes
pulled to opp poles due to shortening of kinetochore spindle fibres
"opposite poles of the cells elongate the whole cell" ??

telophase
chromosomes decondense and uncoil > chromatin threads
spindle fibres disintegrates and nuclear envelop reforms
"nucleoli reappears" ? ( earlier nucleous disappears √ disintegrates x)

cytokinesis
division of the cytoplasm into 2 cells
• animals
cell membrane invaginates
ring of microfilaments contract > cleavage furrow
further shortening of microfilaments eventually separates the two daughter nuclei
• plants
series of fluid vesicles from G.A move along microtuble to middle - phragmoplast ( area of dense cytoplasm)
these vesicles fuse to form the cell plate
vesicular contents contribute to cell wall and its membranes to that of daughter cells

importance of mitosis
* Growth - increases cell no.
*Repair and Replacement - dead,wear and tear
*Asexual reproduction and regeneration - genetically identical and survive in the same habitat

genetic stability
*genetically identical to parent cell,no alterations in the genetic material and replication occurred before mitosis,
sis chromatids arranged to face opp spindle fibres
centromere duplicates and each sis chromatids has it's own


molecular control of cell cycle
cell cycle differences results from regulation at molecular level


G1 checkpoint ( restriction point)
-checks for presence of growth factor √ and DNA damage
G1 arrest if absence of GF or presence of dna damage

G2 checkpoint (DNA restriction checkpoint)
- prevents proliferation of damaged cells

M phase checkpoint (spindle checkpoint) between metaphase and anaphase
-checks for proper attachment of spindle fibres > triggers onset of anaphase
basically this ckpt ensures each daughter cell receives a complete set of chromosome


DNA damage checkpoint
-checks for dna breakage, mispairing of bases > involves p53 protein (coded for tumour suppressor gene) to trigger cell arrest, providing time for repair
if not possible p53 triggers apoptosis (cell death)


cell cycle clock





cancer


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