Apoptosis

Question 1

Apoptosis causes the digits (toes and fingers) to separate from each other during development. Describe the sequence of events

Answer 1

• enzymes break down the cell cytoskeleton
• the cytoplasm becomes dense with organelles tightly packed
• the cell surface membrane changes and blebs form
• the chromatin condenses and the nuclear envelope breaks so DNA breaks into fragments
• the cell breaks down into vesicles that are taken up by phagocytosis and the cellular debris is disposed of so that it does not damage other cells or tissue

Question 2

What is apoptosis?

Answer 2

• it is programmed cell death
• it ensures that the rate of cells produced by mitosis is the same as the rate of cells dying, so the number of cells remains constant
• apoptosis is involved in the development of body plans - mitosis and differentiation create the bulk of the body parts and apoptosis refines the parts by removing the unwanted structures
• e.g. When hands and feet first develop the digits are connected, they are only separated when the cells in the connecting tissue undergo apoptosis

Question 3

How does the correct body plan develop?

Answer 3

• all cells contain genes that code for proteins that promote or inhibit apoptosis
• during development, genes that control apoptosis are switched on and off in appropriate cells so that some die and the correct body plan develops

Question 4

What happens if there is a lack of apoptosis?

Answer 4

It can lead to cancer