6.1.7 The Importance of Mitosis & Apoptosis

Question 1

What is apoptosis? Why?

Answer 1

Programmed cell death of old cells that are not needed anymore

Question 2

How does apoptosis occur? (process)

Answer 2

• DNA of cell becomes denser and more tightly packed
• Nuclear envelope breaks down
• Chromatin condenses
• Phagocytes engulf and digest cell

Question 3

What do proto-oncogenes do?

Answer 3

• Stimulate cell division

Question 4

What do tumour-suppressor genes do?

Answer 4

• Reduce cell division
• Can stimulate cell apoptosis in cells with irreparably damaged DNA
• This protects the body by ensuring cells with damaged DNA are destroyed before potentially leading to cancer

Question 5

How are checkpoints in the cell cycle monitored and why?

Answer 5

• Checkpoints to ensure no genetically damaged cells are produced
• So cell is fully ready for mitosis (DNA damage is all repaired and perfect)
• Regulated by cyclins and cyclin-dependent kinases

Question 6

What do cyclins do?

Answer 6

• Regulate progress of cell through cell cycle
• Activate cyclin-dependent kinases
• Different ones produced a different stages of cell cycle

Question 7

What do cyclin-dependent kinases do?

Answer 7

• Once activated by cyclins
• Act as catalysts
• Can catalyse phosphorylation of target proteins, activating or inactivating them
• Ensures cell cycle progresses from 1 stage to another

Question 8

Examples of internal cell stimuli which genes (monitoring the cell cycle or apoptosis) respond to :

Answer 8

• Irreparable genetic damage
• RNA Decay
• Cellular injury, etc
• Production of Cyclin D
• All initiate apoptosis in cells undergoing CELL STRESS

Question 9

Examples of external cell stimuli which genes (monitoring the cell cycle or apoptosis) respond to :

Answer 9

• Cytokines from immune system
• Hormones and growth factors
• Viruses and bacteria
• UV Light
• Pollutants
  ^ can affect balance of mitosis and apoptosis by destroying cells faster than they can be replaced or made

Question 10

How do cells respond to cell stress?

Answer 10

• Activate pathways to increase chance of survival (counteracting damage)
• Initiate apoptosis (if stress remains and it cannot be repaired, apoptosis occurs)