Problem 79 - A Complete Resource Book in Chemistry for JEE Main

Question

Sanger's reagent is used for the identification of (a) \(\mathrm{C}\) - terminal of a peptide chain (b) \(\mathrm{N}-\) terminal of a peptide chain (c) number of amino acids in a peptide chain (d) side chain of amino acids

Step-by-Step Solution

Answer

Sanger's reagent is used for identifying the -terminal of a peptide chain (b).

Step 1: Understand Sanger's Reagent Use

Sanger's reagent, which is 1-fluoro-2,4-dinitrobenzene (FDNB), is known for its ability to bind to the mino end (10e, 10a-terminal) of a polypeptide chain. This specific action is mainly used to determine the identity of the first amino acid in the chain.

Step 2: Analyze the Options Given

We have four options: (a) 21-terminal, (b) 10-10-terminal of a peptide chain, (c) number of amino acids in a peptide chain, and (d) side chain of amino acids. Sanger's reagent identifies the 10-10-terminal, rather than 21-terminal or the side chains.

Step 3: Identify Correct Usage of Sanger's Reagent

Since Sanger’s reagent is used to label and determine the 10-10-terminal amino acid of a peptide chain, the correct answer is (b) 10-10-terminal of a peptide chain.

Key Concepts

N-terminal identification

The N-terminal of a polypeptide chain is the first amino acid in the sequence, which has a free amino group. Identifying the N-terminal amino acid is crucial for studying the structure and function of proteins. Sanger's reagent, specifically 1-fluoro-2,4-dinitrobenzene (FDNB), plays a vital role in this process. This chemical binds selectively to the free amino group of the N-terminal amino acid. Once bound, it allows for the isolation and identification of this amino acid through analysis techniques such as chromatography or mass spectrometry. Why is identifying the N-terminal important? Knowing the sequence start can offer insights into protein synthesis and regulation. Proteins often have an initiating residue that can dictate the processing and function of the entire molecule. In practical applications, determining the N-terminal residue can also be important in understanding post-translational modifications that may affect protein activity or stability.

Polypeptide chain

A polypeptide chain is a linear polymer consisting of amino acids linked by peptide bonds. It forms the backbone of proteins and determines their structure and function. Each polypeptide chain is composed of a specific sequence of amino acids, which determines how it will fold and what functions it will perform in the body. The sequence begins with the N-terminal, which has a free amino group, and ends with the C-terminal, which has a free carboxyl group. This chain can vary in length, ranging from a few amino acids to several thousand, depending on the protein it constitutes. Understanding the structure of a polypeptide chain is crucial because:

• It helps in understanding how proteins perform their functions at the molecular level.
• Provides insights into the functional domains within proteins that are critical for biochemical reactions.
• Understanding mutations and alterations within the chain can shed light on various diseases and conditions.

Amino acid sequencing

Amino acid sequencing refers to determining the order of amino acids in a polypeptide or protein. Sequencing plays a crucial role in understanding the structure, function, and interaction of proteins. The process generally begins with the identification of the N-terminal amino acid followed by the determination of the subsequent amino acids till the sequence is complete. Techniques such as Edman degradation or mass spectrometry are commonly employed for sequencing, and Sanger’s reagent is instrumental in the initial identification of the starting amino acid. The importance of amino acid sequencing includes:

• Discovering genetic mutations that might alter protein function and lead to disease.
• Aiding in the design of drugs and therapeutic proteins by revealing binding sites and functional domains.
• Helping in evolutionary studies by comparing protein sequences across different species to infer phylogenetic relationships.

Overall, understanding the sequence of amino acids allows scientists to predict the 3D structure of proteins, which is critical in unraveling biological pathways and mechanisms.