Which option about cell cycle checkpoint is correct?
a) the decision to cross the R point is irreversible
b) some decisions made at checkpoints are reversible
c) all decisions made at checkpoints are reversible
d) option a & b
e) option a & c
There are five major transitions between sequential stages of the cell cycle in eukaryotes: G1a/G1b - the ‘restriction or R point’ in mammalian cells, ‘Start’ in yeast; G1/S - initiation of DNA synthesis; G2/M - entry into mitosis; metaphase/anaphase - chromosome alignment on the mitotic spindle; telophase/G1 - exit from mitosis and return to G1 phase. Progression through each of these transitions is irreversible. Thus, the correct answer is a) the decision to cross the R point is irreversible