Question

1. Given that the end of point of apoptosis is the same, describe one way you would expect all of these forms of cell to be the same. (Dead cells is NOT a sufficient answer).

Confused on this question, because one of the earlier question said that some forms of apoptosis do NOT require the activation of the caspases. So i'm not unsure of exactly do they have in common? Is it just that they're revolved around caspase whether it's dependent and independent?

Answer 1

There are two distinct phases in apoptosis, the initiation phase and the execution phase.

The initiation phase involves many different proteins and it is quite complex. It is started by various “stresses” from either outside the cell (extracellular) or inside the cell (intracellular).Some examples of extracellular signals that trigger apoptosis include loss of growth factors, low oxygen levels (hypoxia), and radiation. Intracellular signals include DNAdamage, the damage caused by chemotherapy drugs, telomere malfunction, and infection with viruses.

The initiation phase triggers the execution phase.  

The execution phase involves the activation of specialized enzymes (caspases and others) that directly result in cell death.

During this phase a group of protein-cutting enzymes called caspases lead directly to cell death.

The main execution caspases are caspases-3, 6 and 7. Caspases are present in lethal doses within each cell, but they only become active via the initiation process. Caspase-3 is considered the most important of all the caspases. It can cause DNA and chromatin damage, re-arrange the cytoskeleton, and disrupt intracellular transport, cell division, and signal transduction.

Once activated the execution, caspases cannot be stopped, cell death is certain.

Cell fragments produced during the final stage of apoptosis are quickly recognized, engulfed, and digested by macrophages or surrounding epithelial cells.