Microbiology 20: (Fry) Cell cycle 1 Flashcards
Phases of the cell cycle?
G1 -> growth
S -> Growth and replication of DNA, organelles
G2 -> growth
(interphase)
Meitosis -> segregation of chromosomes
(Cytokinesis) -> Division of cytoplasm + cell division
G0 (stationary phase / quiescence) -> cells that have exited cell cycle (midway through G1)
Why are cells in culture difficult to study?
They are asynchronous -> cell cycles are not in sync
What drugs can be used to stop cells in various phases of the cell cycle?
s-phase: aphidicolin, thymidine
m-phase: nocodazole
Can then wash out drugs to synchronise cells
Ways of measuring cell cycle stages?
1) simple observation via microscope
2) s-phase cells can be detected by radiolabelled nucleotides
Dominance of cell phases revealed by cell fusion experiment?
Meitosis is dominant over all
S phase is dominant over G1, but not G2
G1 - G2 fusion -> does not effect cycle of each nucleus in fused cell
Protein complex responsible for acting as M-phase promoting factor and S-phase promoting factor? Proteins involved in each phase?
Cdk-cyclin complex (heterodimer)
Cdk 1,2, 4 and 6
Cyclin A,B,D and E
Cdk 1 and Cyclin A, and Cdk1 and Cyclin B
-> M-phase promoting factors
Cdk 2 and Cyclin E
-> S-phase promoting factor
Cdk 4 and Cyclin D, Cdk6 and Cyclin D
-> passage through restriction point (in G1 -> further cell cycles)
Cdk 2 and Cyclin A -> passage through S-phase
What is Cdk? Structure? How does cyclin bind?
Cyclin-dependent kinase -> have catalytic cleft
serine/threonine kinase
in inactive conformation in absence of cyclin
cyclin binds via cyclin-box
Differences in expression between cyclin and cdk?
Cdks constantly expressed
- only active in presence of cyclin
Each cyclin is subject to a cyclical pattern of synthesis and degradation during the cell cycle
- different cyclins peak in abundance at different times in the cell cycle thereby activating Cdks at specific times
