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UVic BIOL 360 - Fall 2019 > Apoptosis (ch 18) > Flashcards

Apoptosis (ch 18) Flashcards

1
Q

In humans, how many cells die each hour?

A

Billions.

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2
Q

In humans, how do the rates of cell death and cell replication compare?

A

They are exactly balanced.

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3
Q

Where does the term “apoptosis” come from?

A

Derived from the Greek word for “falling off”.

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4
Q

Is apoptosis the only kind of cell death?

A

No. There are others.

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5
Q

What model organism was critical for early experiments on programmed cell death?

A

C. elegans.

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6
Q

What differentiates apoptosis from necrosis?

A

Apoptosis: regulated, cell engulfed by phagocyte
Necrosis: unregulated, cell spills its shit everywhere

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7
Q

Give an example of how apoptosis is critical during organism development.

A

Removed unwanted cells or structures, such as webbing between digits or extraneous nerve cells.

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8
Q

What molecular technique allows us to biochemically recognize apoptosis?

A

TUNEL technique.

Tdt-mediated dUtp Nick End Labelling

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9
Q

How can phosphatidylserine signal to macrophages that a cell is undergoing apoptosis? What else does this cause?

A

Phosphatidylserine normally present on the cytoplasmic side of the membrane, but flips to the extracellular side during apoptosis. Inhibits production of inflammatory cytokines by the macrophages.

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10
Q

What phospholipid can signal to macrophages that a cell is undergoing apoptosis?

A

Phosphatidylserine on the extracellular side of the cell membrane (normally cytosolic).

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11
Q

How can observation of the mitochondria indicate that a cell is undergoing apoptosis?

A

The mitochondria will release cytochrome c into the cytosol, which can be fluorescently labelled for visualization.

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12
Q

Besides triggering the release of cytochrome c, what other event occurs in the mitochondria during apoptosis?

A

The electrical potential across the inner mitochondrial membrane is lost.

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13
Q

How long does it take for cytochrome c to be released from the mitochondria during apoptosis?

A

Not long, less than 10 minutes.

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14
Q

In what 3 ways do cells die (that we talked about)?

A
  1. Apoptosis
  2. Autophagy
  3. Necrosis
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15
Q

What role do caspases play in the cell?

A

They are the intracellular machinery responsible for apoptosis.

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16
Q

Why are caspases so named?

A

The “c” is from cysteine and the “asp” is from aspartate.

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17
Q

How are caspases activated?

A

By proteolytic cleavage and dimerization with other caspases.

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18
Q

At what amino acid do caspases cleave their protein targets?

A

Aspartic acid.

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19
Q

What are the 2 main type of caspases?

A
  1. Initiator Caspases

2. Executioner Caspases

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20
Q

How are the initiator caspases and executioner caspases related?

A

The initiator caspace cleaves the executioner caspase, triggering it to cleave other substrates and induce apoptosis.

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21
Q

Are caspases synthesized in response to an apoptotic stimuli or are they already present, only requiring activation?

A

They’re already there, just need the green light.

22
Q

As an example of the caspase cascade during apoptosis, what steps lead to DNA fragmentation?

A

Executioner caspase activates CAD by cleaving iCAD from CAD. Active CAD goes on to break DNA.

23
Q

In apoptosis, what differentiates the extrinsic pathway from the intrinsic pathway?

A

Extrinsic: Extracellular signal trigger
Intrinsic: Internal cytochrome c trigger

24
Q

Give an example of apoptosis via an extrinsic pathway.

A

Fas ligand on killer T cells binds to Fas receptors on target. Death-inducing signalling complex (DISC) forms, and then is cleaved to form an initiator caspase, etc.

25
Q

Give an example of apoptosis via an intrinsic pathway.

A

Mitochondria receives apoptotic stimuli, releases cytochrome c (Cyt C). Cyt C binds to an activator which then oligomerizes and recruits caspases, etc.

26
Q

During apoptosis via the intrinsic signalling pathway, what does cytochrome C bind to once it is released from the mitochondria?

A

Apoptotic Protease Activating Factor 1 (Apaf1).

27
Q

During apoptosis via the intrinsic signalling pathway, what domain allows Apoptotic Protease Activating Factor 1 (Apaf1) to oligomerize?

A

Caspase Activation & Recruitment Domain (CARD).

28
Q

During apoptosis via the intrinsic signalling pathway, what is an oligomer of Apoptotic Protease Activating Factor 1 (Apaf1) proteins called?

A

An apoptosome.

29
Q

What initiator caspase is involved in Fas-mediated apoptosis via the extrinsic pathway?

A

Caspase-8 (Cas-8).

30
Q

What initiator caspase is involved in cytochrome c-mediated apoptosis via the intrinsic pathway?

A

Caspase-9 (Cas9) of CRISPR-Cas9 fame!

31
Q

Is digit development more affected by knockout of Cas9 or knockout of Apaf1?

A

Apaf1 believe it or not. You’ll still lose the webbing between your fingers even if you don’t have functioning Cas9, but not without Apaf1.

32
Q

What are 2 examples of proteins which can inhibit apoptosis via the extrinsic pathway?

A
  1. Decoy receptors

2. Intracellular blocking proteins (FLIP)

33
Q

What are some examples (5) of things which can trigger apoptosis via the intrinsic pathway?

A
  1. DNA damage
  2. Injury
  3. Lack of oxygen
  4. Lack of nutrients
  5. No survival signals
34
Q

What is the function of the Bcl2 protein family?

A

To regulate the intrinsic apoptotic pathway, specifically release of cytochrome c from the mitochondria.

35
Q

Is Bcl2 well conserved between species? Would it be interchangeable?

A

Yes. Human Bcl2 even has the same function in nematodes!

36
Q

What 2 proteins in the Bcl2 family are anti-apoptotic?

A
  1. Bcl2

2. BclXₗ

37
Q

What 2 proteins in the Bcl2 family are pro-apoptotic effectors?

A
  1. Bax

2. Bak

38
Q

What 5 proteins in the Bcl2 family are pro-apoptotic BH3-only proteins?

A
  1. Bad
  2. Bim
  3. Bid
  4. Puma
  5. Noxa
39
Q

Which protein domain is the only one shared by all the subcategories of Bcl2 proteins? What domains do the others have?

A

BH3.
Anti-apoptotic: BH1-BH4
Pro-apoptotic effector: BH1-BH3
Pro-apoptotic BH3-only: duh…

40
Q

Either Bak or Bax is needed for the intrinsic apoptotic pathway. What differentiates these?

A

Bak: always bound to mitochondrial membrane
Bax: in cytosol, requires translocation to mitochondria

41
Q

Why is either Bak or Bax necessary for the intrinsic apoptotic pathway to function?

A

Because they aggregate to form channels in the mitochondrial membrane in response to an apoptotic stimulus, allowing cytochrome c (+others) to exit.

42
Q

What effect do Bcl2 and BclXₗ have on the intrinsic apoptotic pathway? How do they function?

A

They are anti-apoptotic, inactivating the intrinsic pathway by inhibiting aggregation of Bax and Bak on the mitochondrial membrane.

43
Q

What effect do Bad, Bim, Bid, Puma, and Noxa have on the intrinsic apoptotic pathway? How do they function?

A

They are pro-apoptotic, inhibiting the anti-apoptotic Bcl2/BclXₗ to allow Bax and Bak to aggregate on the mitochondrial membrane.

44
Q

in the intrinsic apoptotic pathway, how would Bid, Bcl2, and Bak interact?

A

Bid —–| Bcl2 —–| Bak —–> apoptosis
AND
Bid —–> Bak —–> apoptosis

45
Q

How do inhibitors of apoptosis (IAPs) function? Why are they necessary?

A

Bind to the cleaved caspase and inhibit downstream effects. Needed to prevent accidental apoptosis.

46
Q

Beyond simply binding to caspases, some inhibitors of apoptosis (IAPs) __________ caspases.

A

Polyubiquitylate caspases.

47
Q

How are inhibitors of apoptosis (IAPs) removed from caspases once bound?

A

Anti-IAPs are released from the mitochondria with cytochrome c causing the IAPs to unbind from the caspases, allowing apoptosis to proceed.

48
Q

In what 3 ways can a cell respond to an extracellular survival signal?

A
  1. Increase anti-apoptotic Bcl2 production
  2. Inactivate pro-apoptotic BH3-only proteins (by phosphorylation)
  3. Inactivate anti-IAPs
49
Q

In cancer, which Bcl2 family protein is being affected to allow tumour growth?

A

Excessive production of Bcl2 (B Cell Lymphoma!) leading to reduced apoptosis and tumour growth.

50
Q

What cell cycle check does mutation of a p53 tumour suppressor protein allow the tumour to bypass?

A

Cell will proliferate even if the DNA is damaged.

51
Q

What size of band is necessary to be able to recognize apoptosis on an agarose gel?

A

Any size. If it shows up, you’ll be able to tell.

52
Q

What happens in a fly cell if you block anti-IAPs?

A

Block apoptosis by allowing IAPs to block caspases.

UVic BIOL 360 - Fall 2019 (10 decks)

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