Respuesta :
The significance of checkpoints can be demonstrated by considering what happens when they are impaired. What would occur if there was a gain-of-function mutation in the promoter for the cyclin E gene such that cyclin E protein was always made at high levels even under conditions in which cyclin E would not normally be made?
a. Cells will pass through the G2/M checkpoint with damaged DNA.
b. Cells will skip the S phase and go directly to G2 phase and not complete DNA replication.
c. Cells will pass through the G1/S checkpoint even if conditions are not ideal for cell division.
d. Cells will pass the M checkpoint with chromosomes unattached to spindles.
Answer:
c. Cells will pass through the G1/S checkpoint even if conditions are not ideal for cell division.
Explanation:
Cyclins are the regulatory proteins that are formed during different stages of the cell cycle. A specific cyclin during each stage bind to corresponding cyclin-dependent kinases (CDKS). The activated CDKs phosphorylate the proteins required for the progression of a cell through a specific stage of the cell cycle.
For example, Cyclin E is synthesized at the peak near the G1 -S phase transition or G1/S checkpoint. They activate the CDK-2 and allow the cells to progress from G1 to the S phase. If the cell is not prepared for DNA replication, cyclin E is not formed or is inhibited by specific protein kinases which in turn does not allow the cell to enter the S phase.
Any gain of function mutation resulting in the constitutive synthesis of cyclin E would allow the cell to pass through the G1/S checkpoint irrespective of the conditions.
