Download lecture 8

Apoptosis
There are two ways that a cell can die: necrosis and
apoptosis. Necrosis occurs when a cell is damaged
by an external force, such as poison, a bodily injury,
an infection or getting cut off from the bloodsupply
(which might occur during a heart attack or stroke).
When cells die from necrosis, it's a rather messy
affair. The death causes inflammation that can cause
further distress or injury within the body..
Apoptosis
Programmed cell death (Apoptosis) is the process by
which cells in plants and animals die through self –
destruction rather than due to injury.
•Also referred to in animal cells as apoptosis, the process
is typically a part of embryonic development of all animals
and is thought to be responsible for the development of
individual digits and the elimination of excess materials in
various stages of animal development.
Apoptosis
•It is also an element of the immune system in
animals, and the process by which excess or
flawed(become cracked ) cells in the body are
eliminated to maintain homeostasis and health.
• Programmed cell death can also have a
negative effect on the body of an animal or
human being when triggered by viruses.
Apoptosis
•Programmed cell death is thought to be an especially
important part of animal growth and development in early life
and the embryonic stage.
• Examples :
1- Evidence indicates that the early development of individual
fingers and toes in a human fetus is due to the apoptosis of the
cells that would exist between the digits but die off, leaving the
remaining cells to form the individual fingers.
2- The reincorporation of a tadpole’s tail into its body as it
becomes a frog is due to cell death, rather than the continued
division and growth of those tail cells.
Apoptosis
•Unfortunately ..
- programmed cell death can be hindered by certain
viruses and other adverse physiological conditions.
The spread of cancer throughout an animal’s body is
typically due to apoptosis not properly occurring in the
organism’s body. In ideal conditions, cancerous cells
should be ordered to die by proteins in the body,
preventing those cancerous cells from dividing and
spreading.
Apoptosis
• The programmed cell death does not properly occur,
however, in many cases of cancer, leading to the spread
of potentially deadly cells throughout the body. The
human immunodeficiency virus (HIV) similarly uses
programmed cell death in a negative way by causing T
helper cells that typically fight off viruses and other
infections in the human body to begin self-destructing.
This condition, referred to as acquired immunodeficiency
syndrome (AIDS), effectively destroys the body’s immune
system, which often leads to complications or death from
other illnesses.
Apoptosis
• Programmed cell death is an important process in
development, immune defense, and cancer
protection, but it must be regulated to prevent
uncontrolled cell death.
• An inhibitor of apoptosis protein, or IAP, is a type of
protein that is able to stop apoptosis
Apoptosis
• by inhibiting caspases : (proteins that are necessary for the
initiation of apoptosis).
---NOTE : ( Caspases are the primary proteins involved in the
initiation of apoptosis, so naturally, they are the primary targets
of almost every inhibitor of apoptosis).
•They also regulate some transcription factors that are
important for the synthesis of various proteins that lead to
apoptosis.
-It is believed that inhibitors of apoptosis may be related to
tumor formation because one of the characteristics of many
cancerous cells is the inability to undergo apoptosis.
Apoptosis
•There are also regulatory proteins that exist for the
purpose of regulating inhibitors of apoptosis. The
second mitochondria-derived activator of caspase, or
SMAC