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Apoptosis
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Aims:
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Must be able to define the term apoptosis.


Should be able to outline the stages of
apoptosis.
Could be able to explain the purposes of
apoptosis.
Basics
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Apoptosis – Programmed cell death.

A balance is needed between cell replication and cell
death.

If the balance is not regulated then uncontrolled
increase in cells = TUMOUR.

If a tumour continues to grow and invades healthy
tissue = MALIGNANT = CANCER.

Too LITTLE apoptosis can lead to CANCER.

Too MUCH apoptosis can lead to DEGENERATIVE
diseases e.g. Alzheimer’s.
In Detail
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Apoptosis and Necrosis are different.
Necrosis occurs if the cell is damaged causing
damage to the membrane resulting in cells
swelling then bursting.
Apoptosis is controlled as cells respond to signals
from one of two signal pathways:
1. Mitochondrial pathway
2. Death receptor pathway
Mitochondrial Pathway

Signals from inside the cell.

If serious damage occurs inside the cell OR if the
cell is infected with a virus.

Proteins on the surface of the mitochondria are
activated.

Mitochondrial membrane breaks.

Sequence of events triggered including the cutting
DNA with the use of enzymes (CASPASES).
Death Receptor Pathway

Signals from outside the cell.

Could be triggered because:
– Cell not developed fully – E.g. embryonic
brain cells
– More cells than are needed – uses energy to
keep cells alive e.g. immune cells
– No longer useful – E.g. T and B cells after
recovering from a disease. Cells between fingers
and toes in embryonic development.
The Process
1.
Cells receive message from outside using death receptors in cell
membranes or from the breakdown of the mitochondrial membrane.
2.
Many different caspases activated within the cell.
3.
Message sent to phagocytes in the area.
4.
Signalled cells begin to shrink and develop small bumps (BLEBS) on
surface.
5.
Caspases enter through nuclear pores, DNA and proteins in nucleus
are degraded, mitochondria break down.
6.
Other organelles preserved in membrane enclosed fragments.
7.
Phagocytes engulf fragments. Secrete cytokines that inhibit
inflammation.
Apoptosis activated by
intrinsic or extrinsic
pathway
Cell Shrinkage chromatin
condensation
Diagram
Normal Cell
Nuclear
collapse
Lysis of apoptotic
bodies
Apoptotic body
formation
Video
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Apoptosis
Activity
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Answer the questions from p213 in
Biozone books.