Cell Life Cycle 1 Flashcards
What occurs in S phase of life cycle?
DNA replication
What happens at M phase of life cycle?
Mitosis (nuclear division) and cytokinesis (cytoplasm division)
Where is G1 phase?
In the gap between M and S Phase
Where is G2 phase?
In the gap between S and M phase.
What is the kinetochore?
A specialised complex of proteins, where spindle microtubules attach to chromosomes.
What are the three types of microtubule involved in mitotic spindle?
Astral, kinetochore, interpolar
What is cytokinesis?
The creation of two new cells. Partitioning of the 2 nuclei and organelles. Usually symmetric division occurs, unless stem cells which divide asymmetrically.
How is the cell cycle controlled?
Checkpoints exist in cell cycle where biochemical questions are posed. Contingent events regulate the process.
What are cyclin dependent kinases?
Family of enzymes which control the cell cycle, regulated by a subunit called cyclin. CDKs phosphorylate proteins involved in key cell cycle events - both structural and functional.
How is the CDK-cyclin complex formed?
Regulated by phosphorylation and dephosphorylation.
1) cyclin and CDK form an inactive cyclin-cdk complex
2) protein kinase binds two phosphates to the complex - an inhibitory and an activating phosphate
3) protein phosphatase removes inhibitory phosphate, so cyclin-cdk complex becomes active
What is the action of ubiquitin?
Targets cyclin-cdk active complex, causing the destruction of cyclin and thus the inactivation of cdk
What are the different classes of cyclins and when do they work?
S cyclin - activates CDKs just prior to S phase
M cyclin - activates CDKs and regulate entry to mitosis
G1 cyclin - activates CDKs in late G1
How is p53 involved in the cell cycle?
It arrests the cell cycle at G1 checkpoint if DNA damage occurs. Does this by functioning as a transcription factor, to turn on expression of genes that are involved in growth arrest and apostolic cell death.
What is the action of Rb receptors in a resting cell?
They are not activated by mitogens. The Rb protein is dephosphorylated and active, keeping a series of transcription factors in an inactive state. Cell proliferation does not occur.
What is the status of Rb in a proliferating cell?
Mitogens bind and activate signalling pathway, so Rb is inactivated and cell proliferation can occur.
