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Cellular pathology > Cell damage and cell death > Flashcards

Cell damage and cell death Flashcards

1
Q

What are the causes and mechanisms of cell damage/death?

A
  • Genetic
  • Inflammation
  • Physical
  • Traumatic damage
  • Infection
  • Chemical
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2
Q

What are the 3 basic mechanisms which causes cell death?

A
  1. Necrosis
  2. Apoptosis
  3. Autophagic cell death
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3
Q

What is the most common cause of cell death?

A

Necrosis

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4
Q

When does necrosis occur?

A

Occurs after stresses such as ischemia, trauma, chemical energy

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5
Q

What is apoptosis?

A

Programmed cell death

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6
Q

What is apoptosis designed to do?

A

Designed to eliminate unwanted host cells through activation of a co-ordinated, internally programmed series of events affected by a dedicated set of gene products

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7
Q

What is autophagic cell death responsible for?

A

Autophagy is responsible for the degradation of normal proteins involved in cellular remodeling found during metamorphosis, aging and differentiation as well as for the digestion and removal of abnormal proteins

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8
Q

What is the cause of necrosis and give examples?

A 
• Usually caused by lack of blood supply to cells or tissues, e.g.
	○ Injury
	○ Infection
	○ Cancer
	○ Infarction
           Inflammation
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9
Q

What is affected in necrosis?

A

Whole group of cells are affected in necrosis

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10
Q

What is necrosis the result of?

A

Result of an injurious agent or event

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11
Q

What happens if large amounts of water enter cells?

A

If large amounts of water enter, there is irreversible swelling

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12
Q

Steps involved in necrosis

A
  1. Whole group of cells are affected
  2. Result of an injurious agent or event
  3. Energy deprivation causes changes like cell is unable to produce ATP because of oxygen deprivation
  4. As there is no ATP, ion pumps don’t function and hence causing a water influx
  5. Haphazard destruction of organelles and nuclear material by enzymes from ruptured lysosomes
  6. Cellular debris stimulates an inflammatory response
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13
Q

What are the three microscopic appearance of necrosis?

A
  • Nuclear change
  • Cytoplasmic change
  • Biochemical change
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14
Q

What do we observe in nuclear change in necrosis?

A
  1. Chromatin condensation/shrinkage

2. Fragmentation of nucleus

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15
Q

What do we observe in cytoplasmic changes in necrosis?

A
  1. Opacification: denaturation of proteins with aggregation.

2. Complete digestion of cells by enzymes causing cell to liquify (liquefactive necrosis).

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16
Q

What do we observe in biochemical changes in necrosis?

A
  1. Release of enzymes such as creatine kinase or lactate dehydrogenase
  2. Release of proteins such as myoglobin
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17
Q

What is the function of necrosis?

A

• Removes damaged cells from an organism
• Remove cell debris
-Failure to do so may lead to chronic inflammation

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18
Q

What is apoptosis?

A

Selective process for the deletion of superfluous, infected or transformed cells

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19
Q

What are the 2 types of apoptosis and examples?

A 
• Intrinsic
	○ DNA damage – p53-dependent pathway
	○ Interruption of the cell cycle
	○ Inhibition of protein synthesis
	○ Viral Infection
	○ Change in redox state
• Extrinsic 
	○ Withdrawal of growth factors (e.g. IL-3)
	○ Extracellular signals (e.g. 
           TNF)
          § T cell or NK (Natural 
             Killer) (e.g. Granzyme)
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20
Q

What are caspases and what do they play a role in?

A

They are cysteine proteases that play a central role in the initiation of apoptosis

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21
Q

What do caspases do?

A

Cleave proteins that have the cysteine and aspartate residues together

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22
Q

How are most proteases synthesised?

A

Most proteases are synthesised as inactive precursors requiring activation

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23
Q

How can the inactive precursor of proteases be activated?

A

Usually partial digestion by another protease

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24
Q

What are inactive precursors known as?

A

Inactive precursors known as pro-caspases

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25
Q

What is apoptosis mediated by?

A

Apoptosis is mediated by an intracellular proteolytic cascafe

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26
Q

Steps in procaspase activation

A
  • Inactive procaspase Y can be activated by active caspase X

- Large and small subunit form a dimer to form activated form

27
Q

Steps in caspase cascade

A

○ Active initiator caspase (i.e. 8/9) will activate other caspases
○ As a result of this activation, cytosolic proteins that contain cysteine and aspartate residues are cleaved
○ Actin cytoskeleton in cells starts to breakdown
○ Cells start to collapse
○ Caspase can activate other effector caspases (i.e. 1, 3, 6, 7) resulting in amplification of proteolysis
○ Also cleave nuclear lamin which is usually needed for the nuclear envelope

28
Q

What does the caspase activation lead to?

A 
• Caspase activation leads to characteristic morphological changes of the cell such as:
	○ Shrinkage
	○ Chromatin condensation
	○ DNA fragmentation
        ○Plasma membrane 
          blebbing
29
Q

What is the DNA fragmentation of normal cells?

A

One thick band due to high MW so doesn’t run in electrophoresis

30
Q

What is the DNA fragmentation of apoptotic cells?

A

○ Can see clear laddering
○ Fragments
○ In apoptotic cells, nucleosomes and the DNA around them are intact but there is activation of nucleases that cleave within nucleosomes

31
Q

What is the DNA fragmentation of necrotic cells?

A

Smear

32
Q

How is the fragmentation of necrotic cells?

A

Fragmentation of DNA is random because cells do not have nucleosomes

33
Q

What are the 3 microscopic appearances of apoptosis?

A
  • Nuclear changes
  • Cytoplasmic changes
  • Biochemical changes
34
Q

What are the nuclear changes of the microscopic appearance of apoptosis?

A
  1. Nuclear chromatin condenses on nuclear membrane

2. DNA cleavage

35
Q

What are the cytoplasmic changes in the microscopic appearance of apoptosis?

A

○ Shrinkage of cell. Organelles packaged into membrane vesicles
○ Cell fragmentation. Membrane bound vesicles bud off
○ Phagocytosis of cell fragments by macrophage and adjacent cell
○ No leakage of cytosolic components

36
Q

What are the biochemical changes in the microscopic appearance of apoptosis?

A

○ Expression of charged sugar molecules on outer surface of cell membranes (recognised by macrophages to enhance phagocytosis)
○ Protein cleavage by proteases, caspases

37
Q

How do we activate initiator caspase?

A

By induced proximity

38
Q

Examples of induced proximity

A
  • In response to receptor dimerization upon ligand binding

- Cytochrome C release from the mitochondria

39
Q

What is the extrinsic pathway?

A

• Transmembrane receptor can recruit adaptor protein
○ Adaptor protein will make dimers through death domain
○ Can also bring with it inactive procaspase 8
• Cells receive death ligand (TNF)

40
Q

What does TNF induce the formation of?

A

TNF induces the formation of a death inducing signalling complex

41
Q

Steps involved in the formation of DISC

A
  • TNF brings receptors that come together
  • Close proximity brings together procaspase 8
  • Proteolysis of procaspase 8 results in activation
42
Q

What does cytochrome C trigger?

A

Another way of triggering apoptosis

43
Q

What does it mean if cytochrome C is present in the mitochondrial matrix protein?

A

If cytochrome C detected in cytoplasm, indicates cell will die

44
Q

What does cytochrome C have a binding site on?

A

Has a binding site on APAF

45
Q

What does APAF have and what can it bind and recruit?

A

APAF has domain that can bind and recruit procaspases

46
Q

What is the release of cytochrome C regulated by?

A

Regulated by the BCL family

47
Q

What do BCL-2 family members form?

A

BCL-2 family members form dimers

  • Homodimers
  • Heterodimers
48
Q

Examples of antiapoptotic factors

A
  • BCL-2

- BCL-XL

49
Q

Examples of pro-apoptotic factors

A

-Bax

50
Q

Where is Bax located?

A

Bax is located in mitochondrial membrane

51
Q

What do Bax dimers create?

A

Bax dimer creates pore in the middle of the mitochondrial membrane

52
Q

What can cytochrome C be released through and to activate what?

A

Cytochrome C can be released through the pore into the cytosol to activate caspase 9

53
Q

What does BCL-2 form in normal cells and what does this prevent from escaping?

A

In normal cells, BCL-2 forms a ‘lid’ on top of the pore of the dimer so cytochrome C cannot escape

54
Q

What type of signal is Akt/PKB kinase?

A

Is a survival signal

55
Q

What is the substrate of Akt/PKB kinase?

A

Substrate of this is the pro-apoptotic protein BAD

56
Q

Where is BAD located and phosphorylated by what?

A

BAD is in the cytoplasm and can be phosphorylated by AKT

57
Q

What is phosphorylated BAD?

A

Phosphorylated BAD is inactive

58
Q

What happens if the cell stops receiving survival signal?

A
  • Akt is no longer active so cannot phosphorylate BAD

- Excess unphosphorylated BAD can compete with BAX for binding to BCL-2

59
Q

What happens when apoptosis occurs due to DNA damage and what happens if this doesn’t happen?

A

P53 TF is activated which activates transcription of cell cycle inhibitor P21 to stop cell cycle and try to repair DNA
-If this doesn’t happen, P53 will activate transcription of autogenes

60
Q

What is one of the target genes of P53 and what does this mean?

A

• One of target genes of P53 is BAX so increased transcription of BAX

  • Excess of BAX = excess BAX dimers that can create pores for the cytochrome C to pass through
    • This is because there are not enough BCL-2 molecules to act as a lid to the pore
61
Q

What does activation caspase 9 cause?

A

Cell death

62
Q

What are the most common mutations in cancer?

A

Mutations in the p53 gene are the most common mutations in cancer

63
Q

What do some mutations destroy the ability of to induce apoptosis?

A

Some mutations destroy the ability of p53 to induce apoptosis

Cellular pathology (12 decks)

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