Apoptosis and Necrosis

Question 1

What is apoptosis?

Answer 1

Programmed cell death
Apoptosis is a cellular process in which a defined and programmed sequence of intracellular events leads to the removal of a cell without the release of products harmful to surrounding cells

Question 2

When does a cell know to apoptose?

Answer 2

When DNA damage occurs within the cell via base alteration or cross linkage

Question 3

Which protein detects DNA damage?

Answer 3

P53

Question 4

What could happen if there is a mutation in the P53 gene?

Answer 4

Cancer

Question 5

Where is there a lack of apoptosis?

Answer 5

In cancer

Question 6

Where is there too much apoptosis?

Answer 6

HIV - HIV virus can induce apoptosis. It can induce apoptosis in CD4 helper cells which reduces their num- bers enormously to produce an immunodeficient state.

Question 7

What is necrosis?

Answer 7

Necrosis is traumatic cell death which indices inflammation and repair

Question 8

What are regulators of apoptosis? (Inhibitors)

Answer 8

Inhibitors:
Growth factors
Extracellular cell matrix
Sex steroids

Question 9

What are regulators of apoptosis? (Inducers)

Answer 9

Inducers:
Glucocorticoids
Free radicals
Ionising radiation
DNA damage

Question 10

What is the intrinsic pathway for apoptosis?

Answer 10

-Uses pro- and anti-apoptotic members of the Blc-2 family
-Bax forms Bax-Bax dimers which enhance apoptotic stimuli
-The Bcl-2:Bax ratio determines the cell’s susceptibility to apoptotic stimuli
-Responds to growth factors and biochemical stress
-p53 gene induces cell cycle arrest and initiates DNA damage repair
-If damage is difficult to repair, p53 can induce apoptosis

Question 11

What is the extrinsic pathway for apoptosis

Answer 11

-Ligand-binding at death receptors on the cell surface
-Receptors include TNFR1 and CD95
-Ligand-binding results in the clustering or receptor molecules on the cell surface and the initiation of signal transduction cascade
-Caspases are activated, triggering apoptosis
-This pathway is used by the immune system to eliminate lymphocytes

Question 12

What is necrosis in general?

Answer 12

It is the the wholesale destruction of large numbers of cells by some external factor

Question 13

What is coagulative necrosis?

Answer 13

Most common type
Can occur in most organs
Cause by ischaemia

Question 14

What are some clinical examples of necrosis?

Answer 14

• Infarction due to loss of blood supply e.g. myocardial
  infarction, cerebral infarction
• Frostbite
• Toxic venom from reptiles and insects
• Pancreatitis

Question 15

What is liquefactive necrosis

Answer 15

Occurs in the brain due to its lack of substantial supporting stroma

Question 16

What is caseous necrosis

Answer 16

Causes a ‘cheese’ pattern
TB is characterized by this form of necrosis
Important - remember this -

Question 17

Gangrene

Answer 17

Necrosis with rotting of the tissue
Affected tissue appears black due to deposition of iron sulphide (from degraded haemoglobin

Question 18

Why is apoptosis important?

Answer 18

It is an important process in normal
cell turnover in the body which prevents cells with accumulated genetic damage from dividing and producing cells
which might eventually develop into cancer cells.

Question 19

How does a cell apoptose?

Answer 19

The cell triggers a series of proteins which lead to the release of enzymes within the cell
which eventually autodigest the cell. Many of these enzymes are caspases.

Question 20

Why is apoptosis important in health?

Answer 20

Development - removal of cells during development e.g.
interdigital webs
* Cell turnover - removal of cells during normal turnover
e.g. cells in the intestinal villi at the tips, to be replaced
by cells from below