.png)
CELL - APOPTOSIS; NECROSIS; MUTATION; CANCER |FINDYOURSELF
Cell
Apoptosis-Programmed
cell death
•
When
cells are no longer needed or become a threat to that organism, they undergo a
suicidal programmed cell death or also known as apoptosis.
•
This
involves a specific proteolytic cascade that causes the cell to shrink
and condense, to disassemble its cytoskeleton and alters its cell surface so
that its neighbouring macrophage can attach to CM and digest it.
•
Apoptosis
is initiated by activation of a family of proteases called CASPASES.
•
These
are enzymes that are synthesized and stored in cell as inactive PROCASPASES.
•
Mechanism
of activation of caspases are complex but when activated they cleave and
activate other procaspases.
•
A
cascade is triggered which breaks down protein in the cell.
•
Cell
dismantles and its remains are ingested by neighboring phagocytic cells.
•
Mostly
apoptosis occurs in tissues that are remodeled during development.
•
It
is balanced with formation of new cells in healthy adults.
•
Otherwise
body tissues would grow or shrink excessively.
•
Abnormalities
of apoptosis results in neurodegenerative diseases like Alzheimer’s disease,
cancer, autoimmune disorders etc.
•
Some
drugs which are used in cancer chemotherapy induce apoptosis in cancer cells.
Necrosis
•
When
cell die as a result of acute injury, it results in swelling and bursting due
to loss of CM integrity.
•
This
process is called necrosis.
•
Necrotic
cells spill their contents, causing inflammation and injury to neighboring
cells.
Cancer
•
It
is caused by mutation or abnormal activation of cellular genes that control
cell growth and mitosis.
•
Abnormal
genes are called Oncogenes.
•
100
different oncogenes have been discovered.
•
In
cells antioncogenes are also present, which suppress the specific oncogenes.
•
Loss
of or inactivation of antioncogenes leads to cancer.
Why cancer does not develop after every mutation
1. Mutated cells have less survival capability and die.
2. Most mutated cells have normal feedback controls that
prevent excessive growth.
3. Potentially cancerous cells are often destroyed by body’s
immune system before they grow into cancer.
Mutated cells form abnormal proteins, these results in
formation of Abs which destroys them.
4. Usually several different activated oncogenes are required
simultaneously to cause cancer.
•
Not
everyone develops cancer although new cells are forming and mutation must be
taking place in them.
•
It
is b/c of precision with which DNA chromosomal strands are replicated and
also proofreading process which cuts and repairs abnormal DNA strands.
•
Probability of mutation increases more when person is exposed to certain chemical, physical or biological
factors including following:-
1.
Ionizing radiation like x-rays, gamma rays, radioactive substances, UV light predispose to
cancer.
•
Ions
formed in these cases are highly reactive and can rupture DNA strands causing
mutation.
•
2. Chemical substances are capable of mutation, such substances are called CARCINOGENS.
•
E.g.
cigarette smoke causes about one quarter of all cancer deaths.
•
Workers
in plants producing aniline dye derivatives are likely to develop cancer.
•
3.Physical irritants, like some types of food causes continued abrasion of the lining of
intestinal tract.
•
It
can lead to rapid mitotic replacement, which increases the chances of mutation.
•
4. Hereditary tendency, one or more cancerous genes are already mutated in
inherited genome.
•
Only
few additional mutations are required to develop cancer.
•
5. Certain viruses can cause cancer.
•
In
case of DNA viruses, DNA strand of virus insert directly into one chromosome,
causing mutation.
•
In
case of RNA viruses, some carry enzyme called REVERSE TRANSCRIPTASE.
Invasive characteristic of cancer cell
•
The
major differences b/w cancer cell and normal cell are:-
1. Cancer cell does not respect usual cellular growth limits
b/c they do not require same GF that are necessary for growth of normal cell.
2. Cancer cells have less tendency to adhere to one another
and wander through tissues, to enter blood stream and transported throughout
the body.
