In: Biology
Briefly describe what must happen molecularly for the following transitions during the cell cycle:
a. G1 to S
b. G2 to M
c. M to G1
During the cell cycle there are different checkpoints or transitions to ensure safe cell division. During these transitions few notable molecular processes must happen to enter into next phase. These are described briefly below:
A) G1 to S transition is ensured when cell activates cyclin and cyclin-dependent kinases which transcribe genes which will work in S-phase to replicate DNA.
B) After DNA synthesis in S-phase cell enter growth phase called G2 where cell ensure that all the DNA is replicated and not damaged. Also synthesis of proteins are done which will function during division. This is done by activity of cyclin B and CDK1.
C) During the third check point of M to G1 transition, cell ensures that all the chromosomes should have aligned and are under tension from both poles (bipolar tension). This bipolar tension is sensed to ensure to enter into anaphase of the cell cycle. The anaphase promoting complex (APC) does this function. When all above phenomena are ensured and inhibition of APC is removed it start degrading the Cyclin B and cell enters into anaphase.