CELLULAR BIOLOGY

Question 1

What are the phases of the cell cycle?

Answer 1

• G1 phase
• S phase
• G2 phase
• M phase
• G0 phase

Question 2

Which phases of the cell cycle are collectively referred to as interphase?

Answer 2

• G1 phase
• S phase
• G2 phase

Question 3

What is the G0 phase of the cell cycle

Answer 3

A non-dividing state

Question 4

What is quiescence?

Answer 4

Cells in G0 phase temporarily and can return to G1 phase in response to external stimuli

Question 5

List the different tissue categories based on the rate those tissues undergo cell division/go through the cell cycle

give examples for each

Answer 5

• Labile tissues: frequently dividing cells e.g. skin cells
• Stable tissues: cells which divide in response to stimuli e.g. liver cells
• Permanent tissues: non-dividing cells e.g. neurones, skeletal muscle and cardiac muscle cells

Question 6

What is senescence?

Answer 6

Cells is senescence are metabolically active but can no longer divide

Question 7

How do cells enter senescence?

Answer 7

Telomeres one each end of the chromosomes shorten with each cell division, eventually these telomeres are shortened so much that the cell stops dividing and enters senescence

Question 8

Which cell types do not enter senescence?

Answer 8

• Stem cells
• Pathogenic cells
• Neoplastic cells

Question 9

How do certain cells prevent senescence?

Answer 9

The telomerase enzyme synthesises telomeres back onto each end of the chromosomes

Question 10

How does the G1 checkpoint regulate the cell cycle?

Answer 10

Checks for:
- cell growth
- nutrients
- presence of growth factors (mitogens)
- DNA damage/mutations

Question 11

How does the G2 checkpoint regulate the cell cycle?

Answer 11

Checks for:
- Completion of DNA replication
- DNA damage/mutations

Question 12

How does the M checkpoint regulate the cell cycle?

Answer 12

Checks for:
- chromosome attachment to spindle fibres at the metaphase plate during metaphase

Question 13

What are the two tumour suppressor proteins?

Answer 13

• p53
• pRb (retinoblastoma)

Question 14

How does p53 regulate the cell cycle?

Answer 14

1. DNA damage/mutations stimulate p53
2. p53 stimulates the cell to enter G0 phase (to allow for DNA repair) or apoptosis

Question 15

How does pRb (retinoblastoma) regulate the cell cycle?

Answer 15

1. Un-phosphorylated Rb inhibits the transcription factor E2F
2. The presence of mitogens stimulates cyclin D synthesis
3. Cyclin D forms are activated complex with CDK-4 and CDK-6 known as the Cyclin D/CDK-4&6 complex
4. This complex phosphorylates Rb, causing the transcription factor E2F to dissociate from Rb and activate gene transcription, allowing the cell to move from G1 to S phase

Question 16

What are the different types of cell death?

Answer 16

• Apoptosis
• Necrosis

Question 17

Which physiological processes require homeostasis?

Answer 17

• Homeostasis
• Animal development
• Immune system

Question 18

List apoptotic stimulants

Answer 18

• DNA damage/mutations
• Growth factor (mitogen) withdrawal
• Hypoxia
• Ishcaemia

Question 19

Describe the process of apoptosis

Answer 19

1. Chromatin condenses
2. Cytoplasm shrinks and the cell membrane ‘blebs’
3. Cell contents is packaged into membrane bound apoptotic bodies
4. Phosphatidyl-serine is exposed on the surface and recognised by macrophages which engulf the cell fragments

Question 20

What is the key group of enzymes required for apoptosis?

Answer 20

Caspases

Question 21

List necrotic stimulants

Answer 21

• Oxygen deprivation
• Physical agents (mechanical trauma, extreme heat, radiation, electric shock)
• Chemical agents/drugs
• Pathogenic agents

Question 22

Describe the process of necrosis

Answer 22

1. Chromatin clumps together
2. Cell and organelles swell, causing the cell to lyse
3. Cell contents is spilled out into the surroundings, triggering an immune response