Question

What is the first sequenced protein?

• A. Insulin
• B. Hemoglobin
• C. Actin
• D. Myosin

Hint:

Sanger's reagent (dinitrofluorobenzene, DNFB) binds covalently to the free amino group at the N-terminus of a polypeptide chain, allowing the identification of the terminal amino acid after acid hydrolysis.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Protein sequencing is the process of determining the exact linear sequence of amino acid residues in a polypeptide chain.
This discovery laid the foundation for modern molecular biology by demonstrating that proteins are well-defined chemical entities with unique, genetically determined sequences.

Step 2: Detailed Explanation:
In 1951, the British biochemist Frederick Sanger determined the complete amino acid sequence of the hormone insulin.
Sanger used bovine insulin as his model, discovering that it is composed of two polypeptide chains:
- The A chain, consisting of 21 amino acid residues.
- The B chain, consisting of 30 amino acid residues.
These two chains are held together by two interchain disulfide bonds, and the A chain also contains an intrachain disulfide bond.
Sanger developed a chemical reagent, 1-fluoro-2,4-dinitrobenzene (Sanger's reagent), to label the N-terminal amino acids of the peptide fragments.
Through systematic cleavage of the chains into smaller overlapping peptides and analyzing their residues, he successfully reconstructed the complete sequence.
This achievement proved that proteins have a precise, genetically defined primary structure and earned Sanger his first Nobel Prize in Chemistry in 19
Other proteins, including hemoglobin, actin, and myosin, were sequenced much later using advanced automated sequencing methods.

Step 3: Final Answer:
The first sequenced protein is insulin, corresponding to option (A).