Question 1

Fill in the blank: In the intrinsic pathway of apoptosis, a protein called ... is released from the mitochondria into the cytosol and binds to the adaptor protein Apaf1, causing it to oligomerize into a wheel-like assembly called an apoptosome, which then recruits initiator caspase-9 proteins.

Accepted Answer

In the mitochondrial pathway of apoptosis, caspase activation occurs after cytochrome c is released into the cytosol and induces the formation of apoptosomes.

Question 2

Indicate true (T) and false (F) statements below regarding programmed cell death by apoptosis. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTF.
( ) Apoptosis is the final fate of almost all cells in an adult animal.
( ) Even perfectly healthy cells may undergo apoptosis.
( ) DNA damage that cannot be repaired inhibits apoptotic pathways.
( ) Apoptosis is the main form of programmed cell death in plant cells as well as in animal cells.

F
T
F
F

Accepted Answer

Even though the number of apoptotic cell deaths in developing and adult animal tissues is astonishing, not all cells die in this way. Apoptosis is found primarily in animals. It can be triggered in perfectly healthy cells that are no longer needed. Cells with extensive DNA damage can kill themselves by undergoing apoptosis.

Question 3

Which of the following morphological changes is NOT typically seen in a cell that is undergoing apoptosis?&#10;A) The cell rounds up.&#10;B) The nuclear envelope disassembles.&#10;C) The cell swells.&#10;D) Large cells break up into membrane-enclosed fragments.&#10;E) The nuclear chromatin breaks into fragments.

Accepted Answer

While cells undergoing necrosis normally swell and burst, apoptotic cells shrink and condense.

Question 4

Which of the following proteins activates the mitochondrial pathway of apoptosis?&#10;A) The tumor suppressor protein p53, when activated in response to extensive DNA damage.&#10;B) The BH3-only protein Bid, when cleaved by the initiator caspase-8 (from the extrinsic pathway).&#10;C) The anti-IAP protein Omi, when activated by dephosphorylation.&#10;D) The BH3-only protein Bad, when activated by dephosphorylation.&#10;E) All of the above.

Accepted Answer

Activated BH3-only proteins or anti-IAP proteins can result in the activation of the intrinsic pathway of apoptosis. In response to DNA damage that cannot be repaired, the tumor suppressor protein p53 activates the expression of genes encoding BH3-only proteins (such as Puma).

Question 5

Indicate whether each of the following mutations would likely promote (P) or inhibit (I) apoptosis in cells harboring the mutation(s). Your answer would be a four-letter string composed of letters P and I only, e.g. PPPI.
( ) Mutations in the pro-apoptotic effector Bcl2 family proteins Bax and Bak that prevent their association with the outer mitochondrial membrane.
( ) A mutation in the BIR domain of the IAP protein DIAP1 that prevents binding to either caspases or anti-IAP proteins.
( ) A mutation in the anti-IAP protein Reaper that prevents its binding to the IAP proteins.
( ) A mutation in the CARD domain of caspase-9 that prevents its binding to Apaf1.

Accepted Answer

Association of Bax and Bak with the mitochondrial membrane is necessary (although not sufficient) for the activation of the intrinsic pathway of apoptosis. The same is true for the association of procaspase-9 with Apaf1 in apoptosomes. Interfering with the binding of IAPs to the caspases promotes apoptosis, while interfering with the binding of IAPs to anti-IAPs represses apoptosis.

Question 6

v-FLIPs are viral proteins that were first identified as modulators of apoptosis; they contain two death effector domains, which are also found in some initiator caspases such as procaspase-8. These v-FLIP proteins can be recruited to the DISC through the binding of the death effector domain to similar domains in the adaptor proteins, but are otherwise catalytically inactive. What do you think is the effect of v-FLIP expression in the host cell?

A) It promotes apoptosis mainly via the extrinsic pathway.
B) It inhibits the extrinsic pathway of apoptosis.
C) It activates only the mitochondrial pathway of apoptosis.
D) It inhibits the intrinsic pathway of apoptosis.
E) It enhances the caspase cascades in both the intrinsic and extrinsic pathways.

Accepted Answer

By binding to the adaptor proteins, these viral proteins interfere with caspase activation at the death-inducing signaling complex (DISC), and therefore make the cells resistant to Fas-mediated apoptosis, which is normally triggered by cytotoxic lymphocytes and proceeds via the extrinsic pathway.

Question 7

Soon after the discovery of nerve growth factor (NGF), researchers injected newborn mice with rabbit antiserum (i.e. serum that contains antibodies) against NGF. They observed massive nerve cell death compared to appropriate control injections. Up to 99% of the neurons in some parts of the developing peripheral nervous system died after about a week of daily injections. These results suggest that ...

A) NGF signaling sensitizes developing nerve cells to apoptotic signals.
B) developing neurons undergo apoptosis in the presence of rabbit proteins.
C) developing neurons require NGF for apoptosis.
D) developing neurons undergo cell death in the absence of NGF.
E) NGF signaling is sufficient for survival of the developing neurons.

Accepted Answer

The antiserum injection results in the perturbation of NGF function, which is similar to knocking-down NGF using genetic techniques. The increase in cell death after injection suggests that NGF is important for nerve cell survival. We now know that the cells undergo apoptosis in the absence of the survival factor.

Question 8

Indicate true (T) and false (F) statements below regarding programmed cell death by apoptosis. Your answer would be a four-letter string composed of letters T and F only, e.g. TTTF.
( ) Apoptosis is the final fate of almost all cells in an adult animal.
( ) Even perfectly healthy cells may undergo apoptosis.
( ) DNA damage that cannot be repaired inhibits apoptotic pathways.
( ) Apoptosis is the main form of programmed cell death in plant cells as well as in animal cells.

F
T
F
F

Accepted Answer

Contribution to disease can come from either excessive apoptosis (e.g. in strokes) or insufficient apoptosis (e.g. in some autoimmune disease and cancers). The p53 protein normally arrests the cell cycle or initiates apoptosis in response to DNA damage, which explains why the loss of p53 function is of benefit to, and is widely observed in, cancer cells.

Question 9

The Bcl2 family is comprised of anti-apoptotic (A), BH3-only (B), and effector (E) proteins. In the following diagram representing the regulation of the intrinsic pathway of apoptosis, what class of activated Bcl2 family proteins (A, B, or E) corresponds to boxes 1 to 3, respectively? Your answer would be a three-letter string composed of letters A, B, and E only, e.g. ABE.

Accepted Answer

The pro-apoptotic effector Bcl2 family proteins such as Bax and Bak induce the release of cytochrome c and other mitochondrial intermembrane proteins into the cytosol. Anti-apoptotic Bcl2 family proteins, such as Bcl2 and BclXL, inhibit these effector proteins and are in turn inhibited by the pro-apoptotic BH3-only proteins such as Bid and Bim. Some BH3-only proteins may also directly activate Bax and Bak (not shown).

Question 10

For each of the following proteins that are proteolytically cleaved in apoptosis, indicate whether the cleavage is first carried out by an initiator (I) or executioner (E) caspase. Your answer would be a five-letter string composed of letters I and E only, e.g. EEEII.
( ) The initiator caspase-2
( ) The executioner caspase-3
( ) The BH3-only protein Bid
( ) The endonuclease inhibitor iCAD
( ) The nuclear protein Lamin A

Accepted Answer

Initiator caspases are cleaved and activated when brought into proximity. They then cleave and activate their downstream executioner caspases and initiate caspase cascades. Whereas very few other substrates, including Bid, are also cleaved by initiator caspases, the great majority of over a thousand identified caspase substrates are thought to be cleaved by executioner caspases to orchestrate apoptosis.

Question 11

Apoptotic cells are efficiently phagocytosed by neighboring cells or macrophages. Which of the following DOES NOT normally happen in this process?&#10;A) The apoptotic cell releases some of its cytoplasmic content to induce a local inflammatory response.&#10;B) The apoptotic cell exposes phosphatidylserine at its surface, which interacts with receptor proteins on the surface of phagocytes via &#34;bridging&#34; proteins.&#10;C) The apoptotic cell loses or inactivates &#34;don't eat me&#34; signals.&#10;D) The apoptotic cell rounds up and detaches from its neighbors, which facilitates phagocytosis.

Accepted Answer

The answer of Apoptotic cells are efficiently phagocytosed by neighboring...

Question 12

Initiator and executioner caspases share all of the following features EXCEPT that ...&#10;A) they are cysteine proteases (they have a cysteine residue at their active site).&#10;B) their inactive form is a monomer.&#10;C) they undergo cleavage during activation.&#10;D) their active form is a dimer.&#10;E) they are inhibited by IAPs.

Accepted Answer

The answer of Initiator and executioner caspases share all of...

Deck 18: Cell Death