6.1.7 The Importance of Mitosis & Apoptosis

Question 1

What is mitosis

Answer 1

• Cell division producing identical cells for growth, cell replacement and tissue repair

Question 2

What is apoptosis

Answer 2

• Programmed cell death
• Old cells systematically die
• DNA of cell becomes denser
• Nuclear envelope breaks down and chromatin condenses
• Vesicles form containing hydrolytic enzymes
• Phagocytes engulfs and digests cell

Eg. Fingers and toes form as a single unit, then the cells in the separating layer undergo apoptosis and fingers form

Question 3

The control of mitosis

Answer 3

• Proto-oncogenes stimulate cell division
• Tumor-suppressor genes reduce cell division
• Tumor-suppressor genes stimulate apoptosis in cells with damaged DNA
• Ensures any genetically damaged cells (which could lead to weakness or cancer) are destroyed
• Checkpoints in cell cycle include these

Controlled by 2 groups of proteins
- Cyclins
- Cyclin-dependent kinases (CDKs)

Cyclins are regulators, CDKs are catalysts activated by cyclins.

Eg. CDKs, once activated by cyclins, can catalyse phosphorylation of target proteins, activating or inactivating them

Ensures cell cycle progresses from 1 stage to the next