Question

The thiol group is present in:

• A. cystine
• B. cysteine
• C. methionine
• D. cytosine

Answer 1

The correct option is B

cysteine

Explanation for correct option:

Option B. Cysteine

Thiol group:

• A thiol group is a sulfhydryl group consisting of a sulfur atom with two lone pairs, bonded to hydrogen.
• The functional group for the Thiol group is $-\mathrm{SH}$.

Cysteine:

• Cysteine is an amino acid with a molecular formula ${\mathrm{C}}_3{\mathrm{H}}_7{\mathrm{NO}}_2\mathrm{S}$.
• It is a non-essential amino acid that is important for making proteins.

Explanation for incorrect options:

Option A. Cystine is the oxidized dimer form of Cysteine with the molecular formula ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{N}}_2{\mathrm{O}}_4{\mathrm{S}}_2$.

Option C. Methionine is made up of amino as well as carboxylic acid groups. The chemical formula of methionine is ${\mathrm{C}}_5{\mathrm{H}}_{11}{\mathrm{NO}}_2\mathrm{S}$.

Option D. Cytosine is a pyrimidine base with a chemical formula ${\mathrm{C}}_4{\mathrm{H}}_5{\mathrm{N}}_3\mathrm{O}$.

Hence, the correct option is B. The thiol group is present in Cysteine.