True about diphtheria toxin ?
**Core Concept**
Diphtheria toxin is a potent exotoxin produced by Corynebacterium diphtheriae, a gram-positive bacterium. This toxin causes the characteristic membrane formation and tissue damage in diphtheria infection.
**Why the Correct Answer is Right**
The diphtheria toxin works by inhibiting protein synthesis in host cells. It does this by catalyzing the ADP-ribosylation of elongation factor-2 (EF-2), which is essential for the translation of mRNA into protein. This results in the cessation of protein synthesis, leading to cell death and tissue damage. The toxin's mechanism of action is similar to that of other bacterial toxins, such as Pseudomonas aeruginosa exotoxin A.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe the mechanism of action of diphtheria toxin. Diphtheria toxin does not work by inhibiting DNA synthesis.
**Option B:** This option is incorrect as it does not accurately describe the mechanism of action of diphtheria toxin. Diphtheria toxin does not work by activating cellular signaling pathways.
**Option C:** This option is incorrect as it does not accurately describe the mechanism of action of diphtheria toxin. Diphtheria toxin does not work by inhibiting mitochondrial function.
**Clinical Pearl / High-Yield Fact**
The diphtheria toxin is highly toxic, with an LD50 of approximately 1-2 ng/kg. This makes it one of the most potent bacterial toxins known.
**Correct Answer: C. Diphtheria toxin inhibits protein synthesis by catalyzing the ADP-ribosylation of elongation factor-2 (EF-2).**