Question

The amino acid that gives a red-blood colour on treating its sodium fusion extract with sodium nitroprusside is

• A. serine
• B. leucine
• C. threonine
• D. methionine

Hint:

Always remember the sulphur-containing amino acids: Cysteine and Methionine These frequently appear in qualitative analysis and biomolecule questions.

Answer 1

The Correct Option is D

Concept: The sodium nitroprusside test is used for the detection of sulphur-containing compounds. When an organic compound containing sulphur is fused with sodium, sodium sulphide is formed. The sodium fusion extract containing sulphide ions reacts with sodium nitroprusside to produce a characteristic violet or red-blood coloured complex.

Step 1: Identify sulphur-containing amino acids. Among naturally occurring amino acids: Methionine and Cysteine contain sulphur atoms.

Step 2: Examine the given options. Serine: \[ HOCH_2CH(NH_2)COOH \] contains oxygen but no sulphur. Leucine: Contains only carbon, hydrogen, oxygen and nitrogen. No sulphur is present. Threonine: Contains hydroxyl group but no sulphur. Methionine: \[ CH_3-S-CH_2-CH_2-CH(NH_2)-COOH \] contains sulphur. Therefore it gives the sodium nitroprusside test.

Step 3: Conclusion. Since methionine contains sulphur, its sodium fusion extract forms sulphide ions which react with sodium nitroprusside producing a characteristic red-blood colour. Hence, \[ \boxed{\text{Methionine}} \] is the correct answer.