Review Question - QID 217620

These cells that demonstrate membrane blebbing and nuclear condensation (pyknosis) are most likely undergoing apoptosis. Casp3 is an executioner caspase that activates DNA endonucleases in the late stages of apoptosis.

Apoptosis describes programmed cell death in response to either internal or external signals. In contrast to uncontrolled cellular necrosis, apoptosis requires that cells have sufficient ATP and functioning caspase enzymes for cellular degradation so that DNA can be degraded and the cytoskeleton can be broken down. This process characteristically generates DNA segments that are multiples of 180 base pairs since endonucleases cut at internucleosomal regions. Caspases can classically be divided into initiator enzymes (such as Casp8 and Casp9) that regulate the initiation of apoptosis and executioner enzymes (such as Casp3, Casp6, and Casp7) that enable the degradation machinery of the cell.

Degen et al. review the processes by which apoptosis leads to the degradation of genetic material. They find that executioner caspases such as caspase 3 lead to activation of endonucleolytic enzymes.

Incorrect Answers:
Answer 1: Bax is a positive regulator of the intrinsic pathway of apoptosis initiation. It functions by promoting the release of mitochondrial cytochrome c into the cytosol, which in turn activates caspase 9.

Answer 2: Bcl-2 is a negative regulator of the intrinsic pathway of apoptosis initiation. It functions by preventing the release of mitochondrial cytochrome c into the cytosol and thereby inhibiting caspase 9.

Answer 4: FAS is a receptor in the external pathway of apoptosis initiation. It mediates a cascade of caspase activation via FADD, a death domain-containing adapter protein, and can be activated by immune cells.

Answer 5: P53 is a master regulator of cell cycle progression and cell survival. It responds to signals of DNA damage and regulates both positive (Bax) and negative (Bcl-2) factors in the intrinsic pathway of apoptosis.

Bullet Summary:
Caspases are key mediators of apoptosis because they result in the activation of degradation enzymes such as endonucleases.