Lecture 30

Question 1

Describe the function of BH123. (include a description of the number of domains, where it is found, active and inactive states, and what exactly active BH123 does)

Answer 1

BH123 is a pro-apoptotic protein that triggers the intrinsic apoptosis pathway if it is activated

it has 4 domains in the outer mitochondrial membrane that are separated when inactive and aggregate when activated

When activated, BH123 induces the release of cytochrome c and then binds to Apaf1 to form an apoptosome

Question 2

Describe the function of Bcl2 (include it’s location, types, and how exactly it carries out it’s function)

Answer 2

it regulates the intrinsic apoptosis pathway by controlling the release of cytochrome c into the cytosol

it is found on the cytosolic surface of the outer mitochondrial membrane

Anti-apoptotic Bcl2: blocks the release of cytochrome c to promote cell survival

Pro-apoptotic Bcl2: promotes the release of cytochrome c

Question 3

Describe the function of BH3-only (what is necessary for BH3 activity, where is it found/action take place)

Answer 3

BH3 doesn’t do anything until it is activated

after activation, it moves from the cytosol, to the mitochondria where it helps to activate the intrinsic apoptosis pathway

BH3-only inhibits “anti-apoptotic Bcl2 proteins” and basically inhibits the inhibiting Bcl2 protein

This allows the activation of the intrinsic apoptosis pathway and therefor makes BH3-only a “pro-apoptotic”protein

Question 4

What are IAP’s and what is their function? (be sure to state the 2 methods it has for completing it’s function and what “issue” this addresses)

Answer 4

Inhibitors or Apoptosis = IAP

they bind to caspases to block them, or ubiquitinate them to destroy them (either way they prevent the function of caspases)

(this solves the issue of Caspases being able to auto-activate themselves)

Question 5

What are anti-IAP’s and what is their function? (include their origin)

Answer 5

They are proteins from the mitochondria that block the function of IAPs

This allows the apoptosis pathway to occur

Question 6

Describe what is the role of of Bcl2 protein in apoptosis?

Answer 6

it regulates the intrinsic apoptosis pathway by controlling the release of cytochrome c into the cytosol

Anti-apoptotic Bcl2: blocks the release of cytochrome c to promote cell survival

Pro-apoptotic Bcl2: promotes the release of cytochrome c

Question 7

Describe what is the role of of Bcl2 protein in apoptosis? (be specific)

Answer 7

it regulates the intrinsic apoptosis pathway by controlling the release of cytochrome c into the cytosol

Anti-apoptotic Bcl2: blocks the release of cytochrome c to promote cell survival by binding to and inhibiting the aggregation of pro-apoptotic proteins

Pro-apoptotic Bcl2: promotes the release of cytochrome c through the outer mitochondrial membrane

Question 8

describe the molecular structure of the 2 types of Bcl2 proteins

Answer 8

Anti-apoptotic Bcl2: has 4 distinctive domains called Bcl homology domains (BH domains)

Pro-apoptotic Bcl2: includes BH123 protein and BH-3 only protein

BH123 protien has 3 domains

BH3-only protein has only 1 domain

Question 9

List the 4 functions of executioner caspases

Answer 9

cleaves downstream proteins

cleaves inactive endonuclease

Targets cytoskeleton

Attacks cell adhesion proteins

Question 10

List the 4 functions of executioner caspases

Answer 10

cleaves downstream proteins

cleaves inactive endonuclease

Targets cytoskeleton

Attacks cell adhesion proteins

Question 11

True or False: The caspase cascade is irreversible. explain

Answer 11

True

Question 12

In general, describe caspases.

Answer 12

Cystein aspartyle specific protease

targets proteins and cleaves them along their aspartic AA residues

They have Cysteine in their active site

Question 13

describe the maturation process of a caspase

Answer 13

first synthesized as an inactive “procaspase”

an active caspase then cleaves the “prodomains” off of the procaspase

the large and small subunits (what is left after prodomain cleavage) then come together to form a heterodimer that is an active caspase

Question 14

True or false: Large quantities of Caspases are synthesized prior to apoptosis activation. explain

Answer 14

False

caspases are always present in all cells, they simple wait to be activated by an internal or external stimuli

(initiator caspases can auto-activate as well and thats no bueno)

Question 15

In terms of apoptosis pathways, the intrinsic pathway is mitochondria _____ and the extrinsic pathway is mitochondria _____.

Answer 15

dependent

independent

Question 16

Explain the molecular structure and presentation of death receptors within a cell membrane

Answer 16

They are transmembrane proteins with 3 domains

An extracellular binding domain
A single transmembrane domain
An intracellular death domain

they exist in homotrimers (3 proteins of the same type that remain associated with one another)

Question 17

Explain the Extrinsic apoptotic pathway (starting with Fas, ending with executioner caspase)

Answer 17

Fas ligand binds to death receptor on the cell surface (both are homotrimers)

death receptor’s intracellular”death domain” recruits FADD (Fas associated death domain) and procaspase-8

a trimer of FADD and procaspase-8 come together to form DISC (death inducing signal complex)

The formation of DISC activates (cleavage into mature caspase) procaspase-8

active caspase activates downstream executioner caspase (caspase-3)

Question 18

Describe and state the function of Decoy receptors and FLIP.

Answer 18

Decoy receptors: basically mimic death receptors on the surface of a cell, however they bind to the Fas ligand and then DO NOT activate apoptosis

FLIP: is a protein that resembles an initiator procaspase and competitively inhibits procaspase-8 and procaspase-10.

(both resemble apoptotic pathway molecules, but prevent apoptosis “act as sponges”)

Question 19

Explain the intrinsic apoptotic pathway

Answer 19

cytochrome c is released from the mitochondria, into the cytosol where it binds to Apaf1

several Apaf1 (apoptotic protease activating factor-1) bound to cytochrome c, come together to form an apoptosome

The apoptosome activates caspase-9 (initiator caspase)

Caspase-9 activates caspase-3 which is an executioner caspase that begins it’s apoptotic activities

Question 20

Name an executioner caspase that is common to both the intrinsic and extrinsinc apoptotic pathways.

Answer 20

caspase-3

Question 21

Chromosome translocation can occur and cause excessive ____ to be made, which causes B cell lymphoma

Answer 21

Bcl2

Question 22

Give 2 examples of condition that occur as a result of excessive apoptosis

Answer 22

heart attacks and strokes

Question 23

If p53 is mutated to the point that it can no longer carry out it’s normal functions, what happens to the cell?

Answer 23

apoptosis is no longer promoted by p53 so cancer can develop