KEGS Biology Blog


YEAR 13 Wednesday 5th December F215
December 4, 2012, 9:29 pm
Filed under: Uncategorized

Apoptosis and Homeobox genes

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Apoptosis

Definition: Programmed cell death

Most cells can only replicate 50 times. This is called Hayflick’s Constant. This is because an area of chromosomes shortens every time the cell replicates. Eventually the DNA is eroded which causes a frameshift. To avoid this cells are programmed to die after 50 replications.

Apoptosis is controlled by cell signalling such as cytokines including nitric oxide which make the inner mitochondrial membrane more permeable.

Apoptosis Sequence of Events:
1. Enzymes break down the cell’s cytoskeleton
2. cytoplasm becomes dense and organelles are tightly packed.
3. cell surface membrane changes and small bits called blebs form
4. chromatin condenses and nuclear envelope breaks. DNA breaks into fragments
5. cell breaks into vesicles, taken up by phagocytosis. The cellular debris is quickly disposed of so it does not damage other cells.

This all happens very quickly.

Apoptosis is also involved in cell deletion. For example, deletion of cells between digits avoids webbed hands and feet.

Homeobox Genes:
control the development of the body plan of an organism, including the polarity (which end of head or tail) and positioning of the organs.

Example: Fruit Fly (Drosophilia melanogaster) by changing the homeobox genes the fly can have legs instead of antennae.

Fruit Fly is used because it reproduces quickly so results of changes can quickly be seen.

Comment by bethanysmith2012




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