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Bio 360 - Cell Biology > Topic 8 - Apoptosis > Flashcards

Topic 8 - Apoptosis Flashcards

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1
Q

What is Apoptosis?

A
  • programmed cell death (but not the only kind - necrosis: premature death of cells in living tissue by autolysis)
  • greek word for “fallin off”
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2
Q

On what organism was apoptosis reintroduced as a legitimate pathway

A
  • idea proposed in the 70s, only 20 years later was it agreed upon based on C. elegans study
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3
Q

What is the difference between Apoptosis and Necrosis

A

Necrosis: swelling, bursting, mess from inflammatory response
Apoptosis: shrink and condense - cytoskeleton collapses - nuclear envelope disassembles - chromatin condenses - Blebs (apoptotic bodies) - Macrophages engulf these Blebs

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4
Q

When is programmed cell death critical?

A
  • during early development; when unwanted structures are eliminated
  • further regulates cell numbers and does a quality control
  • ex. frogs lose their tails, their fingers reshape
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5
Q

The purpose of Apoptosis is to…

A
  • eliminate abnormal cells; assisted by the immune system by checking for cells with self antigens
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6
Q

What does rapid turn over refer to?

A
  • the rapid response to an infection leads to more cells produced that can be supported by survival factors – a challenge in cancer and infections
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7
Q

What is the TUNEL Technique?

A
  • apoptosis can be biochemically recognizable via observing fragmented DNA through gel electrophoresis
  • Tdt-mediated dUTP nick end labelling
  • this refers to knicking DNA at linker regions between nucleosomes
  • in this technique the Terminal Deoxynucleotidyl Transferase (Tdt adds labelled dUTP to 3’ -OH of DNA
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8
Q

How does phosphatidyl serine function with apoptosis?

A
  • this PS is typically on the cytoplasmic side of the membrane
  • during apoptosis though, it will flip to the extracellular side to function as a signalling molecule to macrophages
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9
Q

What is unique about the PS apoptotic method?

A
  • PS-dependent phagocytosis inhibits the production of inflammation inducing signals (cytokines) by the phagocytic cell
  • it provides a signal for macrophages who do not respond to self antigens
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10
Q

What role does mitochondria play in apoptosis?

A
  • during apoptosis the mitochondria will loose the electron potential across the inner membrane (the site for cytochrome C)
  • this cause the relocation of cytochrome C enzyme from the intermembrane space to the CYTOSOL
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11
Q

How can you identify the location of cytochrome C to determine the status of the cell?

A
  • a cytochrome-C-GFP and a mitochondrial Stain will co-localize the position of the cytochromce
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12
Q

Is cytochrome c released slowly over time or rapidly?

A
  • Cytochrome C is released rapidly within 5 minutes

- it precedes flipping by the phosphatidyl serine

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13
Q

What are the Caspases?

A
  • family of proteases with a cysteine in their active sites which cleave specific aspartic acid AA***
  • they are synthesized as Pro-caspases which require proteolytic cleavage performed by other caspases to activate themselves
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14
Q

What intracellular machinery is responsible for apoptosis?

A
  • apoptosis machinery is always present in the cell but in the INactive form
  • a family of proteases called Caspases with cysteine in their active sites but cleaving the target at the aspartic acids
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15
Q

What components form the caspase?

A
  • adapter binding domain
  • protease domain with cleavage sites
  • require the activation from an adapter protein
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16
Q

Who are the initiator Caspases? how are they activated?

A
  • Caspase 2,8,9,10

- an external signal will lead to the formation of the procaspases into activation complexes by cleaving themselves

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17
Q

Who do Caspase 2, 8, 9, 10 activate via cleavage?

A
  • Executioner Caspases are: Caspase 3,6,7

- these will perform as Caspase Cascade = Death Signal

18
Q

What are the targets of the Executioner Caspases?

A
  • nuclear laminas
  • cytoskeletal components
  • cell-cell adhesion proteins
  • DNA endonuclease (cleaves the regions between nucleosomes)
19
Q

What sort of cascade is the Caspase Cascade?

A
  • Caspase cascade is irreversible

- it amplifies the proteolytic cascade

20
Q

What is the Extrinsic apoptotic pathway?

A
  • The apoptotic pathway induced by the immune system

- a killer lymphocyte displaying Fas Ligand will bind the Fas Death Receptor displayed on its membrane

21
Q

Explain the Fas Ligand/Receptor, the DISC and how the immune system regulated this process?

A
  • Fas Receptors on the infected cell forms homotrimers
  • while FasL is part of the TNFalpha signalling protein family (Tumour Necrosis factor)
  • in the target cell the DISC complex will form (Death-Inducing-Signalling-Complex) consisting of the: 1. Death domain FADD (Fas-Assocciated-Death-Domain) 2. Adapter domain 3. Death effector domain (Caspase 8)
22
Q

What is an interesting point about the Death receptors?

A
  • they can also trigger NON-apoptotic pathways which would lead to a survival and inflammation response
23
Q

Who are the decoy receptors or FLIPs?

A
  • the decoy receptors have ligand binding domain but no death domain
  • the FLIP: is the intracellular blocking protein which resembles the initiator procaspase 8 but lack any proteolytic activity - so it functions as a competitior
24
Q

When would an intrinsic apoptotic pathway be initiated?

A
  • in response to stress, lack of oxygen, or injury to the cell
  • for mammals response is dependent on the release of mitochrondrial intermembrane proteins
  • Cytochrome C binds and activates the apoptotic protease activatin Factor 1
25
Q

Who is ApaF?

A
  • Apoptotic Protease Activating Factor 1
  • when cytochrome C is released into the cytosol it will bind to Apaf-1
  • the active Apaf-1 contains CARD (Caspase-Activating-Recruitment-Domain)
  • this will initiate the formation of the apoptosome and recruitment of Caspase 9
  • the Apoptosome will activate the Caspase 9 which cleaves the nearby executioner caspases
26
Q

Apoptosome?

A
  • activated by CARD (Caspase activation recruitment domain) on Apaf-1 (apoptotic protease activating factor-1)
27
Q

Which protein family regulates intrinsic apoptosis? who form what?

A

Bcl2 proteins - heterodimers

- B cell Lymphoma

28
Q

Who are the anti-apoptotic Bcl2 family proteins?

A

Bcl2, BclXL

29
Q

Who are the pro-apoptotic Bcl2 family proteins?

A
  • Bax, Bak
30
Q

Who are the pro-apoptotic BH3-only proteins?

A
  • Bim, Bad, Bid, Puma, Noxa
31
Q

The balance between what determines if a cell lives or dies?

A
  • pro-apoptotic and anti-apoptotic activity
32
Q

The two pro-apoptotic Bcl2 protein regulators?

A
  • apart of the BH123 family
    Bax: cytosolic and translocates into the mitochondrial membrane with an apoptotic signal
    Bak: tightly bound to the outer mitochondrial membrane ALWAYS
33
Q

How are Bak and Bax activated?

A
  • they are dependent on the being activated by the pro-apoptotic BH3 only (Bad, Bim, Bid)
  • these 3 link apoptotic activity to stimulate intrinsic apoptosis
34
Q

Who is apart of the anti-apoptotic Bcl2 family? and what do they do?

A

Bcl2 and BclXL who both site on the mitochondrial membrane

  • these two will inhibit the BH123 family (Bax, Bak)
  • they preserve membrane integrity, prevent release of mitochondrial proteins & release Ca2+ from the ER
35
Q

Who does the intrisic pathway proceed?

A
  • requires the anti-apoptotic Bcl2 proteins to be inactivated by the inhibitors from the BH3 only Bcl2family
36
Q

The BH3-only proteins function in what way?

A
  • Bim, Bid, Bad directly interact with Bax and Bak to assist in their activation
  • Bim: JNK (MAP kinase) activation leads to intrinsic pathway
  • Puma and Noxa: after DNA damage, after increased p53, puma and Noxa are transcribed and intrinsic pathway is activated
  • Bid: Caspase 8 will cleave Bid, tBid will inhibit the Bcl2 and triggers apoptosis via BH123
  • Bad and Bim: form heterodimers with anti-apoptotic Bcl2 and Bcl-XL for pro-apoptotic activity
37
Q

BH3 only proteins regulate the intrinsic pathway

A
  1. If no survival signal received, a MAP kinase cascade will turn on BH3-Bim for apoptosis
  2. the transcription of genes encoding BH3 only proteins Puma and Noxa will trigger the intrinsic pathway
  3. The extrinsic pathway can activate the intrinsic pathway - active Caspase8 cleaves Bid, where Bid translocates to the outer mitochondrial membrane where it inhibits anti-apoptotic Bcl2
38
Q

A triple knockout of Puma, Puma Bim, and Puma Bim Bid compared to a Wildtype examined what?

A
  • the Wild Type had normal Caspase 3 activity while reduced
39
Q

What are the IAPs?

A
  • the Inhibitors of Apoptosis
  • who bind and inhibit activated caspases by setting a threshold (some may poly-ubiquitylate caspases)
  • these IAPs set an inhibitory threshold that must be overcome before apoptosis can be active again
40
Q

Who are the Anti-IAPs?

A
  • these IAPs will translocate the IAP’s to block the anti-apoptotic threshold
41
Q

What are the Three Survival Factors?

A

A) Increased production of the Anti-Apoptotic Bcl2 Proteins - will block oligomerization thus blocking apoptosis
B) Inactivation of pro-apoptotic BH3-oly Bcl2 proteins - this will inhibit Bad: which will release active Bcl2 which prevents oligmerization blocking apoptosis
C) the inactivation of the anti-IAP: the last kinase will phosphorylate HID via an anti-IAP which inhibits IAP

Bio 360 - Cell Biology (10 decks)

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