True about apoptosis
**Core Concept**
Apoptosis is a highly regulated cellular process of programmed cell death, essential for maintaining tissue homeostasis and eliminating damaged or unwanted cells. This process involves a series of complex biochemical events, including mitochondrial outer membrane permeabilization, activation of caspases, and DNA fragmentation.
**Why the Correct Answer is Right**
Apoptosis is characterized by the activation of a cascade of cysteine proteases, known as caspases, which cleave various cellular substrates, leading to the characteristic morphological changes of apoptosis, such as cell shrinkage, membrane blebbing, and DNA fragmentation. The mitochondrial pathway of apoptosis is initiated by the release of cytochrome c from the mitochondrial intermembrane space, which binds to Apaf-1 and triggers the formation of the apoptosome complex, leading to the activation of caspase-9 and subsequent activation of caspase-3.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because apoptosis is a highly regulated process that involves the activation of specific caspases and is not simply a result of cellular stress or injury.
**Option B:** This option is incorrect because autophagy is a distinct cellular process that involves the degradation of cellular components, whereas apoptosis is a programmed cell death process.
**Option C:** This option is incorrect because necrosis is a form of cell death that occurs due to cellular injury or infection, whereas apoptosis is a programmed cell death process.
**Clinical Pearl / High-Yield Fact**
One important aspect of apoptosis is its role in cancer, where dysregulation of the apoptotic pathway can lead to uncontrolled cell growth and tumor formation. Understanding the mechanisms of apoptosis is crucial for the development of targeted therapies for cancer.
**Correct Answer:** D.