the cell cycle

Question 1

state what the cell cycle is and outline its stages

Answer 1

regulated cycle of division with intermediate growth periods
1. interphase
2. mitosis / meiosis (nuclear division)
3. cytokinesis (cytoplasmic division)

Question 2

outline what happens during interphase

Answer 2

G1: cell synthesises proteins for replication e.g. tubulin for spindle fibres and cell size doubles
S: DNA replicates = chromosomes consist of 2 sister chromatids joined at a centromere
G2: organelles divide

Question 3

how is the cell cycle regulated?

Answer 3

• checkpoints regulated by cell-signalling proteins ensure damaged cells do not progress to next stage of cycle
• cyclin-dependent kinase enzymes phosphorylate proteins that initiate next phase of reactions

Question 4

describe what happens at each key checkpoint in the cell cycle

Answer 4

• between G1 and S, cell checks for DNA damage (e.g. via action of p53), after restriction point, cell enters cycle
• between G2 and M, cell checks chromosome replication
• at metaphase checkpoint, cell checks that sister chromatids have attached to spindle correctly