Cell cycle

Question 1

What are the basic stages of the cell cycle?

Answer 1

1. Interphase
2. Prophase
3. Metaphase
4. Anaphase
5. Telophase
6. Cytokinesis

Question 2

What happens during Interphase?

Answer 2

• DNA is replicated and checked for errors
• Protein synthesis occurs in the cytoplasm
• Mitochondria grow and divide, increases number in cytoplasm
• Chloroplasts grow and divide in plants and algal cell cytoplasm, increases in size
• Cell respiration can occur during Interphase and many other processes.

Question 3

What are the three stages of Interphase?

IMPORTANT: Can you explain the process?

Answer 3

• G1 - Proteins are synthesised and organelles replicate. Cell increases in size
• S - synthesis phase : DNA is replicated in the nucleas
• G2 - Second growth phase: cell continues to grow in size, energy stores increased and DNA checked for errors

Question 4

What is the ‘Mitotic phase’?

Answer 4

• Where cell division occurs
• Consists of:
  
  • Mitosis - nucleas divides
  • Cytokinesis - cytoplasm divides and two cells are produced

Question 5

How would you explain G0?

CHALLENGE: Can you give an example where a cell in G0 can return back to the cell cycle?

Answer 5

• where cell leaves the cycle temporarily or permanently
• whether its for differentiation, permanent cell arrest however growing numbers of senescent cells can result in cancer/arthritis

CHALLENGE: An example where this happens is when lymphocytes are produced in a immune response.

Question 6

How is cell division monitored for DNA errors/needs for repairs or if it’s grown to the right size?

Answer 6

• Checkpoints are used at G1 & 2.
• G1 checkpoint - End of G1 phase before entry in S phase and if cell DOES satisfy requirements triggers DNA replication if NOT cell enters a resting state (G0).
• G2 checkpoint - End of G2 stage before mitotic phase. If DNA had been replicated without error, then cell initiates beginning of mitosis.

Question 7

How is the passing of a cell-cycle checkpoint brought by and explain process on a whiteboard?

Answer 7

• Brought by kinases
  
  • class of enzyme that catalyses phosphorylation.
• Tertiary structure of cyclin (checkpoint protein) changes, this activates CDK complex when appropriate kinase binds to correct cyclin.
• CDK complex catalyse activation of key cell cycle proteins by phosphorylation.
  
  • ensures cell progresses through different phases at appropriate times.
• Different enzymes break down cyclin when they’re not needed to signal a cell to move into the next phase of the cycle.

-

Question 8

How can cell cycle regulation and cancer be related?

CHALLENGE: what solution can there be for this?

Answer 8

• If there is a way to control the activity of CDKs then it may reduce/stop cell formation and prevent cancer formation.
• Cancer from tumours is a result of a mutation that affect formation of proteins such as checkpoint proteins, processes within the cell cycle.
  - overexpression of the cyclin gene from a mutation disrupts regulation of cell cycle and results in tumors and uncontrolled cell division.

CHALLENGE : If the activity of CDKs can be reduced it may reduce/stop cell division and cancer formation.