Control of cell numbers

What are the importance of controlling cell numbers (3)?

• Regulates homeostasis in multicellular organisms

• Needed for growth and tissue formation

• Needed for tissue maintenance and repair

What are the phases of the cell cycle?

1. G₁ phase

2. S phase

3. G₂ phase

4. M phases - mitosis and cytokinesis

What do Cyclin-CDKs do?

Regulate the cell cycle by:

• Regulating DNA replication, mitosis and cytokinesis

• Regulating entry into different phases of the cell cycle

• Controlling checkpoints

What is the function of p53 in regulating the cell cycle?

• Pauses the cell cycle by inhibiting cyclin-CDK complexes, causing cell arrest

• Promotes DNA repair

• Can trigger programmed cell death if the cell is severely damaged. This prevents the spread of mutation

What is the function of Rb protein in regulating the cell cycle

• Inhibits cell cycle progression

• When growth factors are present cyclin-cdk phosphorylates and inhibits Rb

• Prevents uncontrolled division

What is apoptosis?

A built in suicide programme, that eliminates cells that are no longer needed or have sustained severe damage

List 2 feature of apoptosis

1. Membrane breaks down

2. Phagocytosis of apoptotic bodies by macrophages

How can apoptosis be controlled?

• Survival factors secreted by other cells block apoptosis

• Signals from other cells can trigger apoptosis

List 3 chemical reactions which damage DNA

1. Depurination - when a nucleobase is lost

2. Deamination - when a cytosine amine group is turned into a uracil

3. Ultraviolet radiation - causes thymidine dimers

Name 2 tumour suppressor genes

1. p53

2. Rb

What is a proto-oncogene

Proteins that promote entry into the cell cycle, or proteins that protect cells from apoptosis

What is tumour progression?

A multistep pathway caused by the loss of tumour suppressor genes and gain of oncogene activity

What is an oncogene?

A gene that when mutated or abnormally activated, can cause normal cells to become cancerous by promoting uncontrolled cell growth and division

What are tumour suppressor genes?

Anti-growth genes that are inactivated in cancer cells, both copies require inactivation for the growth control to be lost