Apoptosis

Question 1

What is apoptosis?

Answer 1

The controlled death of a cell.

Question 2

What is necrosis?

Answer 2

The uncontrolled death of a cell.

Question 3

What are the mechanisms of apoptosis?

Answer 3

Enzymatic breakdown: Enzymes break down cells cytoskeleton.
Cell shrinkage: Cytoplasm becomes more dense, and organelles become tightly packed.
Blebbing: Cell surface membrane changes and forms small protrusions called blebs.
Fragmentation: Nucleus breaks down and DNA is cleaved into fragments.
Apoptotic bodies: Cell breaks down into several membrane bound vesicles.
Phagocytosis: Bodies are quickly ingested by phagocytosis so cell debris does not damage neighbouring cells.

Question 4

Why do we need apoptosis?

Answer 4

• For development (shaping body parts)
• Homeostasis (maintaining correct number of cells)
• Immune system (removing B and T lymphocytes that might attack the body)
• Disease prevention (removing cells with damaged DNA)

Question 5

What role does apoptosis have in nervous system refinement?

Answer 5

The body produces more neurons than it needs, so neurons that do not make useful synaptic connections are targeted and destroyed by apoptosis.

Question 6

What role does apoptosis have in metamorphosis?

Answer 6

When tadpoles metamorphasise into frogs, the tail must be removed by apoptosis, catalysed and stimulated by thyroxine, the tail is removed and the nutrients are recycled for their legs.

Question 7

What role does apoptosis have in limb development?

Answer 7

Apoptosis removes the cells between fingers in early development of hands, and failure of this leads to syndactyly.

Question 8

What is the P53 gene?

Answer 8

The P53 gene codes for a protein which acts as a tumor suppressor if and hen DNA damage is detected, so P53 triggers apoptosis.

Question 9

What internal stimuli can influence and trigger P53?

Answer 9

DNA damage, and mitochondrial stress.

Question 10

What external stimuli can influence and trigger P53?

Answer 10

Cell signalling molecules, like cytokines or hormones.

Question 11

Why is it better for cells to die via apoptosis rather than necrosis?

Answer 11

Because necrosis means that the contents of the cell are released, so that leads to inflammation, whereas apoptosis means that the contents of the cell is not released and is recycled, so does not cause inflammation and is more efficient.

Question 12

Describe the role of apoptosis in the development of an embryo. [3]

Answer 12

• Early development, fingers are originally webbed.
• Cells between fingers broken down and fingers made clear and shaped.
• Failure leads to syndactyly.

Question 13

Explain why the cell components are broken down into membrane-bound apoptotic bodies rather than the cell bursting? [2]

Answer 13

• Contents releasing via necrosis leads to inflammation
• Contents are preserved via apoptosis, more efficient and nutrients can be recycled and used for other developments.

Question 14

State what is meant by a homebox gene.

Answer 14

A hoembox gene is a homeotic regulatory gene that codes for the homeodomain. The gene product binds to DNA, initiating transcription.