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Lecture

BIOL 2021 Lecture Notes - G0 Phase, Chromosome Segregation, Gene Duplication


Department
Biology
Course Code
BIOL 2021
Professor
Julie Clark

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BIOL 2021- April 30 2009
CELL CYCLE- CHAPTER 17
- All cells come from pre existing cells
- Cell cycle = cycle of a cell growth and division
- Replicate chromosomes and segregate to daughter cells
- Organelles replicate and segregate
- Increase in mass coordinator with division
- S phase and M phase are the most important
Major Events in cell cycle
- S phase: DNA synthesis (chromosome duplication)
- M phase: chromosome segregation and cell division (mitosis and cytokinesis)
4 phases
- GAP= G1 + G2

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- When cells are taking time for growing and monitoring environment to assess whether
conditions are favourable for growth
- Cell cycle: GI->S->G2->mitosis->G1
- Cells can have a G0 phase which is a resting phase
Exit from G1 to G0
- End of G1 there is a START PHASE
Commit to divide
Irreversible (cant go back, must continue in the cycle)
- Cell cycle:
a) G1+S+G2= INTERPHASE
b) MITOSIS
STAGES OF MITOSIS -> Pannel 17.1
1) Prophase
- DNA is already replicated
- Sister chromatids condense
2) Prometaphase
- Chromosomes start to attach to spindle
- Nuclear membrane begins to breakdown in animal cells
3) Metaphase
4) Anaphase
5) Telophase
- Daughter chromosomes are at poles
- Nuclear envelop
6) Cytokinesis
- Contractile ring contracts creating cleavage
Principles of cell cycle control
- Principles are similar in all eukaryotes
- Yeast mutants defective in genes for cell cycle
I.e. Cdc gene mutant
Control of cycle:
CHECKPOINTS

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1) START= enter cell cycle (point of no return)
Is environment favourable?
2) G2/M: entry into mitosis
Looks to see if DNA synthesis is complete
Looks to see if environment is favourable
3) Metaphase/anaphase transition
Are chromosomes attached to spindle
Spindle attachment checkpoint
- Checks are biochemical switches
Initiate events
Block progress if there’s a problem
- Many of the steps are controlled by CYCLIN DEPENDANT KINASE (CDK)
Never active without cyclin protein
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