Control of The Cell Cycle

Question 1

Progression of the cell cycle is controlled by checkpoints

Answer 1

Checkpoints are mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met.

Question 2

Cyclin proteins accumulate during cell growth and are involved in regulating the cell cycle.

Answer 2

Cyclins combine with and activate clyin-dependent kinases (CDKs). Active cyclin-CDK complexes phosphorylate proteins that regulate progression through the cycle. If sufficient phosphorylation is reached, progression occurs.

Question 3

G1 checkpoint

Answer 3

The G1 checkpoint is near the end of the G1. Here the cell size is monitored. This checkpoint controls entry to the S phase. If go-ahead signal is not reached at the G1 checkpoint, the cell may switch to its non-dividing state called G0, where no cyclin proteins are produced.

At the G1 checkpoint, retinoblastoma protein (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication.

Question 4

G2 checkpoint

Answer 4

The G2 checkpoint is at the end of G2. At the G2 checkpoint, the success of DNA replication and any damage to DNA is assessed.

DNA damage triggers the activation of p53 that can stimulate DNA repair, arrest the cell or cause cell death

Question 5

Metaphase checkpoint

Answer 5

Metaphase checkpoint is during metaphase and controls progression for metaphase to anaphase.

At the metaphase checkpoint, progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules.

Question 6

Proto-oncogene

Answer 6

A proto-oncogene is a normal gene, usually involved in the control of cell growth or division, which can mutate to form a tumour-promoting oncogene.