Ladder pattern of DNA electrophoresis in apoptosis is caused by the action of:
## Core Concept
The question tests the understanding of apoptosis, specifically the biochemical changes that occur during programmed cell death. Apoptosis is characterized by DNA fragmentation, which can be visualized as a "ladder" pattern on agarose gel electrophoresis. This pattern is due to the cleavage of DNA into internucleosomal regions.
## Why the Correct Answer is Right
The correct answer, **C. Endonuclease (specifically, caspase-activated DNase or CAD)**, is right because during apoptosis, caspases activate an endonuclease that cleaves the DNA between nucleosomes. This results in fragments of approximately 180 base pairs or multiples thereof, creating the characteristic ladder pattern on DNA electrophoresis. This process is a hallmark of apoptotic cell death and is crucial for the elimination of unwanted or damaged cells.
## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because while **A. Transglutaminase** plays a role in apoptosis by cross-linking proteins, it is not directly responsible for the ladder pattern seen in DNA electrophoresis.
- **Option B:** This option is incorrect as **B. Protease** is a broad category of enzymes, and while caspases (a type of protease) are crucial in the apoptotic pathway, the direct cause of DNA laddering is not a protease but an endonuclease activated by caspases.
- **Option D:** This option is incorrect because **D. Phospholipase** is involved in the signaling pathways of apoptosis, particularly in the formation of ceramide from sphingomyelin, but it does not directly cause the ladder pattern in DNA electrophoresis.
## Clinical Pearl / High-Yield Fact
A key point to remember is that the ladder pattern on DNA electrophoresis is a diagnostic feature of apoptosis. This feature distinguishes apoptosis from necrosis, where DNA degradation is more random and does not produce a clear ladder pattern. Understanding this difference is crucial in research and clinical settings for studying cell death pathways.
## Correct Answer: C. Endonuclease.