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Week Number: 15
Seminar Date: Wednesday 15th November
Time: 10am-11am
An Introduction to Apoptosis
Apoptosis is an important mechanism that has been adopted across biology, we need to
understand this to understand how our bodies work. Apoptosis is the regulation of cell within
cellular entities, used to kill cells deliberately when it needs to at the right rate.
Apoptosis is an old term, originating from apo=from and ptosis=falling. It was first coined
in 1972 by Andrew Wyllie and John kerr, when looking into the microscope they noticed that
the cells change their morphology, break apart and die. They termed this Apoptosis.
It is important to separate types of cell death, there are two types:
Necrosis: this is where a cell dies in an untimely way due to uncontrolled external factors.
For example, when someone is injured, there is a chance of bacteria entering the blood
stream, in severe cases this can cause gangrene and cell death.
Apoptosis: this is controlled cell death that maintains the rate of cell growth.
In one case the cells burst and trigger an immune response, on the other case the cells
separate and don’t trigger an immune response.
For example, there are two things that could happen:
-The cell could burst and spill out, causing an inflammatory response. i.e. scepsis
-The cells kill themselves by digesting their content while maintaining the bilayer of the cell,
meaning the contents do not spill out.
Cell division occurs all the time, how does your body maintain cell number? It kills cells
regularly in an ordinary fashion. This maintains cell numbers in the body.
Video of Apoptosis – ‘Cellular apoptosis – R. Sabbatini’
In the video the immune cells are moving around, and protrusions are coming out of the cell,
checking on any damaged cells. One of the cells changes rapidly and looks like it is
bubbling, this is apoptosis.
Your liver has cells that are constantly dividing, there needs to be a programme that controls
the number of cells. This is called Apoptosis. If you did not have cell death, you would end
up having 2 tones of bone marrow and a gut 16 km long. This helps maintain the number of
cells and remove infected cells.
Apoptosis is linked to stress responses, too much stress can damage the cell. If the
damage is great, apoptosis will be triggered, and the cell will be killed.
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, I.e. Sunburn – exposing yourself to UV damages your skin cells and in some cases cannot
be repaired. The pealing of your skin is the killing of the cells through apoptosis.
This can also happen with other stresses, any stress the cell receives has hard wired
apoptosis. For example:
- DNA damage
- Cytoskeletal damage by chemotherapeutics
- Hold/cold
- Medicated stress
- Metal stress
I.e. A heart attack causes damage to the heart tissue. As your heart starts to back up you
have lots of oxidated damage to your heart which lead to apoptosis and tissue damage.
Metamorphosis examples:
o A frog losing its tail, this change in shape is due to apoptosis.
o Digit formation - in all vertebrae embryos your digits are webbed. In some this
webbing is gone or reduced, this is from apoptosis to form the embryo shape.
o Nervous system- when your brain develops you make many neurons. These
neurons’ try to find synaptic junctions between each other, if they fail to do this they
are killed by apoptosis. This is the pruning of neuron cells to form a final product.
Every aspect of your biology is governed by killing and producing cells in a regular
fashion. When apoptosis fails to occur, it can cause webbed feet, or the body constantly
grows tissue and form tumors.
How does it work?
The process was initially worked out in a nematode worm, which also goes through
apoptosis. Every cell in these worms has a mapped lineage so biologists know exactly how
many cells they have and how many times they divide. They noticed of the 1100 cells found
in a worm 131 of these cells are killed as the cell develops. This is important if you want to
create the same phenotype. These researchers then found out which genes controlled this
process, one of the genes is controlling cell death. If you take this cell out, cell death no
longer happens.
Robert Horvitz – key figure.
‘Genetic pathway of PCD in C.Elegans’
A healthy cell à the decision for the cell to die à committed to cell death à get killed à
chopped into smaller bits for the immune system to engulf.
This process is conserved. When looking closer, they began to map these processes.
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