Question

The peptide that gives positive ceric ammonium nitrate and carbylamine tests is :

• A. Lys-Asp
• B. Ser-Lys
• C. Gln-Asp
• D. Asp-Gln

Answer 1

The Correct Option is B

To determine which peptide gives positive results for the ceric ammonium nitrate and carbylamine tests, we need to understand what these tests detect:

1. Ceric Ammonium Nitrate Test: This test is used to detect the presence of alcohols. It involves the oxidation of alcohols by ceric ammonium nitrate, leading to a color change (usually to red or reddish-brown).
2. Carbylamine Test: This test is used to detect primary amines. In the presence of alcoholic potassium hydroxide (KOH) and chloroform, primary amines form isocyanides (carbylamines), which have a very foul smell.

From the above information, we conclude that a peptide showing positive results for both tests must contain both an alcohol group and a primary amine group.

Let's analyze each peptide:

1. Lys-Asp: Contains Lysine, which has an amino group (but it is a part of the peptide backbone, not free) and Aspartic Acid, which has a carboxyl group. This peptide will not give a positive test for the ceric ammonium nitrate test as it lacks an alcohol group.
2. Ser-Lys: Contains Serine with an alcohol group (R-OH) and Lysine with a primary amine group (R-NH_2). This satisfies the conditions for both tests to be positive, as Serine provides the alcohol group and Lysine provides the primary amine group.
3. Gln-Asp: Contains Glutamine and Aspartic Acid. While it may have an amide group, it lacks a primary amine and an alcohol group, so it fails both tests.
4. Asp-Gln: Similar to Gln-Asp, this contains Aspartic Acid and Glutamine, which do not provide an alcohol group for the ceric ammonium nitrate test or a primary amine for the carbylamine test.

Thus, the only peptide that would give positive results on both the tests is Ser-Lys, as it contains an alcohol group from Serine and a primary amine group from Lysine.

Correct Answer: Ser-Lys