L12- Cell cycle: controlling when to divide Flashcards
What are the steps in the cell cycle in mitosis?
M- Mitosis (division) G1- Gap1- Cell gets ready to divide S- synthesis phase G2- gap 2 cell grows in size so it can become 2 cells divides..
When is the cell cycle not the same?
Meiosis, early embryogenesis, polyploid cells.
Is there an S phase between divisions 1 and 2 in meiosis?
No. There’s no second DNA replication.
What’s the difference about the cell cycle in early embryos? (xenopus)
First 12 cell cycles have no G1 or G2 phases- cells get smalls
What must the cell do for the cell cycle to happen?
- Decide if environment permits cell division (signals)
- Duplicate DNA ONCE
- Grow before dividing (size)
- Duplicate other cellular structures
- Seperate DNA (mitosis) before the rest of the cell (cytokinesis).
Which direction can the cell cycle be?
Must be unidirectional. Once the cell has committed to divide and duplicate- there shouldn’t be a way to go back.
What controls the phase transition?
MPF- maturation promoting factor
What does MPF consist of?
2 subunits: cyclin and a cyclin-dependent kinase (cdk)
When is cdk present and when is it active?
Cdk is always present but inactive without cycling. Cyclin accumulates at phase transition. Active cyclin- cdk complex drives the cell cycle forward.
What ensures the cycles of cyclin accumulation are at the correct time?
Production and degradation of cyclin. This ensures unidirectionality.
What are cycling dependent kinases:
- regulated by?
- Inactivated by?
- Phosphorylation
2. degradation
Which phase are chromosomes replicated in?
S-phase
What holds sister chromatids together after replication?
Cohesins
What are condensins activated by?
Phosphorylation by M-Cdk
