Topic 5 Cell Division: The Cell Cycle

Question 1

• Consists of G1, S, G2, and M (miotic) phase

- Regulated by molecular signals in cytoplasm

Answer 1

Cell Cycle

Question 2

• Cell increases in size and proteins and ribosomes are synthesized
• G1 checkpoint ensures all is ready for DNA synthesis
• Most variable in length

Answer 2

G1

Question 3

• DNA synthesis occurs

- New DNA molecule replicated form first providing sister chromatids

Answer 3

S

Question 4

• Rapid cell growth
• Organelles replicated
• Genetic material prepares for cell growth

Answer 4

G2

Question 5

• More time spent in interphase (G1, S, G2) than mitosis (90 % of cell)
• Growth occurs in all 3
• Checkpoints:
  a. First and most important at end of G1: cell growth assessed, and favorable conditions checked. If fails, cell enters G0, a non-dividing state. Some cells (liver and kidney) can be induced out of G0, but nerve and muscle cells are permanently there
  b. Second at end of G2 where cell checks for sufficient Mitosis Promoting Factor levels. The accuracy of DNA replication is evaluated
  c. Third at M and occurs during metaphase. Checks if all chromosomes are attached to kinetochores. Triggers start of anaphase.

Answer 5

Key Points