JEE Main 2022 · 29 July · morning · Numerical answer · +4 / −0
In a linear tetrapeptide (Constituted with different amino acids), (number of amino acids) - (number of peptide bonds) is ________.
Answer and solution
Answer 1
Solution
Chemistry ma’am · 3 steps
Four amino acids in a chain need only three links between them, so the difference is always one.
- Peptide bond. A peptide bond, -CO-NH⁻, forms when the -COOH of one amino acid condenses with the -NH₂ of the next, losing one H₂O. Each bond joins exactly two neighbouring amino acids.
- Count the links. A tetrapeptide has 4 amino acids in a row: AA₁-AA₂-AA₃-AA₄. There is one bond between each neighbouring pair, so there are 3 peptide bonds.
peptide bonds = n - 1 = 4 - 1 = 3
- So. Number of amino acids minus number of peptide bonds = 4 - 3 = 1. Using different amino acids changes the sequence, not the count.
The common slip: 0. Counting four peptide bonds, one per amino acid, gives 0. The two ends of a linear chain are a free -NH₂ and a free -COOH, so there are only three bonds.
The idea to keep. A linear chain of n amino acids always has n - 1 peptide bonds, like n beads joined by n - 1 links. Only a cyclic peptide has n bonds.
Answer from the NTA final answer key. Solution by PrepWiser.