199. Which of the following are the sulfur containing amino acids?
i. Methionine
ii. Histidine
iii. Leucine
iv. Cysteine
A. (ii) and (i)
B. (i) and (iv)
C. (iv) and (ii)
D. (iii) and (ii)

Answer: B. (i) and (iv)

Explanation:

Sulfur-containing amino acids are those that contain a sulfur atom in their side chain. In this case:

• Methionine (i): Methionine contains a sulfur atom in its thioether group (-CH2-S-), which makes it a sulfur-containing amino acid.

• Cysteine (iv): Cysteine contains a thiol group (-SH), which also contains sulfur, making it another sulfur-containing amino acid.

The other options:

• Histidine (ii): Histidine does not contain sulfur; it contains a nitrogen-containing imidazole group.

• Leucine (iii): Leucine is a non-polar, aliphatic amino acid that does not contain sulfur.

Conclusion:

The sulfur-containing amino acids in the list are methionine (i) and cysteine (iv), so the correct answer is B. (i) and (iv).