Apoptosis Practice Questions

Correct answer: Cytoplasmic shrinkage and chromatin condensation

Apoptosis is characterized by cell shrinkage and the condensation of chromatin (pyknosis), which keeps the cellular contents contained. Unlike necrosis, this process does not involve membrane rupture or the release of inflammatory signals into the extracellular space.

Correct answer: Mitochondrion

The intrinsic or mitochondrial pathway is triggered by internal cellular stress, leading to mitochondrial outer membrane permeabilization. This results in the release of pro-apoptotic factors like Cytochrome c into the cytosol.

Correct answer: Bcl-2 protein family

The Bcl-2 family contains both pro-apoptotic (e.g., Bax, Bak) and anti-apoptotic (e.g., Bcl-2, Bcl-xL) members. The ratio and interaction between these proteins determine whether the cell will initiate the apoptotic program.

Correct answer: Executioner caspases

Caspases are cysteine-aspartic proteases that exist as inactive zymogens. Once activated, executioner caspases (like caspase-3) cleave key structural and regulatory proteins, leading to systematic cell death.

Correct answer: Sculpting digits by removing interdigital tissue

Apoptosis is essential for morphogenesis, specifically in sculpting the hands and feet. The programmed death of cells in the interdigital regions allows for the separation of individual fingers and toes.

Correct answer: Cytochrome c

Cytochrome c, normally involved in the electron transport chain, is released into the cytoplasm during apoptosis. It binds to Apaf-1 and procaspase-9 to form the apoptosome complex, which activates initiator caspases.

Correct answer: Cleavage of DNA into 180-200 bp internucleosomal multiples

Activated endonucleases cleave the DNA at internucleosomal linker regions during apoptosis. This results in DNA fragments that are multiples of the nucleosome length, appearing as a characteristic 'ladder' on an electrophoresis gel.

Correct answer: Death receptors (e.g., Fas or TNF receptor)

The extrinsic pathway starts when external signaling molecules, such as Fas ligand (FasL), bind to transmembrane death receptors. This binding recruits adapter proteins that activate initiator caspase-8.

Correct answer: Phosphatidylserine

In healthy cells, phosphatidylserine is restricted to the inner leaflet of the plasma membrane. During apoptosis, it flips to the outer leaflet, allowing macrophages to recognize and engulf the cell without inducing inflammation.

Correct answer: They disable a checkpoint that triggers apoptosis after DNA damage

p53 is a tumor suppressor that normally induces apoptosis if DNA damage is irreparable. Mutations in p53 prevent this programmed death, allowing damaged cells to survive and proliferate, contributing to tumor progression.

Correct answer: Bcl-2 protein

Bcl-2 is the prototypical anti-apoptotic protein that prevents the release of Cytochrome c by stabilizing the mitochondrial membrane. Its overexpression is often linked to the survival of cancer cells.

Correct answer: They are phagocytosed by neighboring cells or macrophages

Apoptotic bodies are membrane-bound vesicles containing cellular debris. Their rapid phagocytosis ensures that toxic cellular contents and enzymes do not leak into the surrounding environment, preventing tissue damage.

Correct answer: By eliminating self-reactive T-lymphocytes in the thymus

Negative selection in the thymus uses apoptosis to eliminate T-cells that recognize 'self' antigens. This process is critical for preventing autoimmune diseases and ensuring self-tolerance.

Correct answer: Caspase-8

Caspase-8 is the primary initiator caspase for the extrinsic pathway, activated by the Death Inducing Signaling Complex (DISC). Caspase-9, by contrast, is the initiator for the intrinsic pathway.

Correct answer: ced-9

In the nematode C. elegans, ced-9 encodes a protein that inhibits cell death, functioning similarly to the human Bcl-2 protein. Loss-of-function mutations in ced-9 lead to excessive cell death during development.

Correct answer: Follicular lymphoma

Follicular lymphoma is often caused by a translocation that overexpresses the Bcl-2 gene, which inhibits apoptosis. Conversely, neurodegenerative diseases like Alzheimer's are characterized by excessive or inappropriate apoptosis.

Correct answer: They bind and inhibit active caspases

IAPs are a group of proteins that can directly bind to and inhibit both initiator and executioner caspases. This provides a final layer of regulation to prevent accidental cell death.

Correct answer: Severe DNA damage caused by UV radiation

Internal stressors like DNA damage, oxidative stress, or nutrient deprivation trigger the intrinsic pathway. Fas ligand binding is the classic trigger for the extrinsic pathway.

Correct answer: Nuclear lamins and cytoskeletal actin

Caspases target the cytoskeleton and nuclear lamins for degradation. The breakdown of these structural supports causes the cell to lose its shape and develop the protrusions known as blebs.

Correct answer: It sacrifices the infected cell to curtail further viral replication

Many cells will undergo apoptosis when they detect viral infection, effectively destroying the 'viral factory.' Consequently, many viruses have evolved mechanisms to produce proteins that inhibit the host's apoptotic pathways.