This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
The mechanism by which mercury causes damage ? 
Select and explain. 
A. Binds to -SH group of enzyme, B. Directly toxic, C. Inhibits ETC, D. Inhibits protein synthesis
A: Binds to -SH group of enzyme
Answer: A: Binds to -SH group of enzyme 
Explanation: Ans. is 'a' i.e., Binds to -SH group of enzyme Heavy metal toxicity is caused by tight binding of a metal such as mercury (Hg), lead (Pb), aluminium (Al), or iron (Fe) to a functional group of enzyme. Mercury, for example, binds to reactive sulfhydryl groups (-SH) in the active site of so many enzymes, that it has been difficult to determine which of the inhibited enzyme is responsible for mercury toxicity. Lead also has high affinity for sulfhydryl group.