Cell cycle

Question 1

Name the 5 main stages of the cell cycle

Answer 1

G0, G1, S, G2, M

Question 2

What are the 5 stages of Mitosis

Answer 2

Prophase - nuclear membrane breaks down, spindle appears, chromosomes condense
Prometaphase - Spindles attach to chromosomes, chromosomes condense further
Metaphase - chromosomes align on metaphase plate
Anaphase - sister chromatids separate at the centromere and are drawn to opposite poles
Telophase - new nuclear membranes form, spindle disappears, chromosomes decondense

Question 3

What are the three cell cycle checkpoints

Answer 3

G1/S (restriction) checkpoint
G2/M checkpoint
Metaphase / Spindle checkpoint

Question 4

How is the cell cycle regulated by cyclins and cyclin-dependent kinases

Answer 4

Cell cycle checkpoints are regulatory pathways that control the order and timing of cell cycle transitions ensuring critical evens are completed with high fidelity.
The Cell Cycle is regulated by heterodimeric protein kinases composed of:
Cyclins - Form the regulatory subunit and have no catalytic activity.
Cyclin-dependent kinases (CDKs) - Inactive in the absence of a partner cyclin. Becomes the catalytic subunit of an activated heterodimer which phosphorylates target proteins to orchestrate coordinated entry into the next phase of the cell cycle.
CDKs are constitutively expressed whereas Cyclins are synthesised at specific stages in response to various external stimuli / molecular signals.

Question 5

What is the role of p53 in cell cycle regulation

Answer 5

p53 (“the guardian of the genome”) plays an important role in controlling progression through G1/S and G2/M checkpoints
DNA damage Activated p53 Inhibits progression through checkpoint