BIO 1140 Lecture Notes - Lecture 10: Caspase, Apoptosis, Xylem

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8.5h – Some Cells Are Programmed to Die
Apoptosis: the death of cells that occurs as a normal and controlled part of an organism’s
growth or development.
Programmed cell death
Common to all multicellular eukaryotes
The corpses of dead cells are engulfed and eaten by neighboring cells
Why are nematodes useful model organisms to study apoptosis?
All adult nematodes have exactly the same number of cells
The fate of each of these cells can be tracked
131 out of 1090 die – always
Protease: an enzyme that breaks down proteins and peptides.
Caspase: a protease involved in programmed cell death.
The main “executioner” enzyme
What are the causes of cell death by apoptosis?
Nuclear DNA degradation
Mitochondrial malfunctioning
Sometimes perfectly normal and healthy cells die by apoptosis!
Cells that make up the xylem elements in vascular tissue of woody plants function as
“skeletons” – they must die to fulfill their function as water-conducting pipes
CELL-DEATH GENES: APOPTOSIS
Examples…
Developing fingers and toes are initially connected by tissue, but later some of these
cells die by apoptosis – results in separated fingers and toes.
From caterpillar to butterfly, many tissues of the larva break down by apoptosis
Apoptosis results from?
Gene activation in response to molecular signals from receptors on the surfaces of
marked cells
These signals are death notices, delivered at specific times in embryonic development
When the receptor is activated, it leads to activation of proteins that kill the cell
Killing proteins are inactive in the absence of the death signal
Two proteins needed to turn on the cell-death program:
1. CED-4
2. CED-3
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