mechanism of disease II

Question 1

what are causes of necrosis (step by step)?

Answer 1

usually lack of blood supply

1. result of an injurious agent or event
2. initial events are reversible, later ones are not.
3. lack of oxygen prevents ATP production.
4. cells swell due to influx of water (ATP is required for ion pumps to work)
5. lysosome rupture ; enzymes degrade other organelles and nuclear material hapzardly
6. cellular debris released, triggering inflammation

Question 2

what is the nuclear changes in appearance of necrosis?

Answer 2

nuclear changes :

1. chromatin condensation/shrinkage
2. fragmentation of nucleus
3. dissolution of the chromatin by DNAse

Question 3

what is the cytoplasmic changes in appearance of necrosis?

Answer 3

1. opacification: protein denaturation & aggregation

2. complete digestion of cells by enzymes causing cells to liquify

Question 4

what is the biochemical changes in appearance of necrosis?

Answer 4

1. release of enzymes such as creatine kinase or lactate dehydrogenase
2. release of other proteins such as myoglobin

Question 5

Give an example of necrosis.

Answer 5

• Astrocytoma

- beginning of tumour growth, as tumour gets bigger blood supply moves further away inducing necrosis.

Question 6

What are functions of apoptosis?

Answer 6

• selective process for deletion of superfluous, infected or transformed cells.

Question 7

What is apoptosis involved in?

Answer 7

• embryogenesis
• metamorphosis
• normal tissue turnover
• endocrine -dependent tissue atrophy
• a variety of pathological conditions.

Question 8

What causes apoptosis (step by step)?

Answer 8

1. programmed cell death of one or a few cells.
2. events are irreversible and energy (ATP) dependent.
3. cells shrink as the cytoskeleton is disassembled
4. orderly packaging of organelles and nuclear fragments into membrane bound vesicles.
5. new molecules are expressed on vesicle membranes that stimulate phagocytosis of these organelles packaged, with an inflammatory response.

Question 9

What is the cytoplasmic changes?

Answer 9

1. shrinkage of cell. Organelles packaged into membrane vesicles.
2. cell fragmentation. Membrane bound vesicles bud off.
3. phagocytosis of cell fragments by macrophages and adjacent cells,
4. no leakage of cytosolic components

Question 10

What are morphological features of apoptosis?

Answer 10

• Transmission EM (cytoplasm shrinks around nucleus)

- Scanning EM (vesicles and tubules bud of from the membrane)

Question 11

What are nuclear changes?

Answer 11

1. nuclear chromatin condenses on nuclear membrane.

2. DNA cleavage.

Question 12

What are biochemical changes?

Answer 12

1. expression of charged sugar molecules on outer surface of cell membrane (recognised by macrophages to enhance phagocytosis)
2. cleavage of protein by proteases.

Question 13

What does DNA fragment of apoptosis /necrosis look like?

Answer 13

When run on agarose gel with a DNA fragment stimulated

1. with apoptosis inducing agent you observe laddering, small fragments.
2. necrosis = non- specific digestion leads to DNA smear.

Question 14

What are examples of apoptosis?

Answer 14

1. metamorphosis : tadpole loses tail by apoptosis and becomes frog.
2. interdigital web loss : toes not separated, ie. humans tool (syndactyly)

Question 15

What are caspases?

Answer 15

1. cysteine aspartate -specific proteases

2. important cysteine proteases for apoptosis in both intrinsic and extrinsic causes of apoptosis.

Question 16

What regulates a living cell?

Answer 16

• a continuous balance between signals telling a cell to live(survival) or die (apoptosis)
  1. survival :
• cell - matrix contacts
• growth factors
• cytokines
  2. apoptosis
• disruption of cell-cell /cell-matrix contacts
• lack of growth factors
  3. DNA damaging
  4. death domain ligands.

Question 17

What are 2 types of apoptosis?

Answer 17

1. intrinsic
   - DNA damage -p53 dependent pathway
   - interruption of cell cycle.
   - inhibition of protein synthesis
   - viral infection (only when its withIN the cell it causes apoptosis =intrinsic)
   - change in redox state.
2. extrinsic
   - withdrawal of survival factors, eg. mitogens
   - extracellular signals (eg. TNF)
   - T cell or natural killer

Question 18

How do caspases activate and cleave proteins?

Answer 18

• inactive pro Caspase Y is cleaved to remove NH2 by another active caspase X to make an active caspase y
• initiator caspases activate themselves when in close proximity.
• activation, therefore, means bringing initiator caspases together

-Caspases form an activation cascade, where one cleaves and activates the next (analogous to kinase cascades)

Question 19

What does caspase activation lead to?

Answer 19

-caspase activation leads to characteristic morphological changes, such as shrinkage, chromatin condensation, DNA fragmentation and plasma membrane blebbing.

Question 20

what causes extrinsic apoptosis?

Answer 20

• tumour necrosis factor (TNF) binds to tumour necrosis factor receptor
• this activates death inducing signalling complex
• this stimulates to activate procaspase 8, which departs from the membrane and transports to the cytoplasm where it is activated by the caspase cascade.

induced by ligand binding to receptors, causing receptor dimer/multimer -isation
-multimerisation of receptor leads to cascade of events.

Question 21

Cytochrome C is essential for apoptosis, how is the release of cytochrome C from mitochondria regulated?

Answer 21

• BCL2 protein has pro apoptosis factors and anti apoptosis factors
• pro apoptosis = Bax,Bad,Bid = facilitate cytochrome C release
• anti apoptotic = bCL2 = inhibit cytochrome C release
• the pro and anti apoptosis factors can dimerise (more than one factor binds)and if there are more pro factors release is favoured.

Question 22

If BCL2 proteins are regulated by cytochrome C what regulates cytochrome C?

Answer 22

• gene expression
• post transcriptional modification
  1. Transcription driven by TP53
  2. Phosphorylation ie. growth factors