Glycine and alanine combine to form a dipeptide. Show how the peptide bond is formed between them, and state what small molecule is released in the process.

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Accepted Answer

Peptide bond formation is a condensation reaction between the carboxyl group ( $-\text{COOH}$ ) of one amino acid and the amino group ( $-\text{NH}_2$ ) of a second amino acid. Taking glycine's carboxyl group and alanine's amino group as the reacting pair: the $-\text{OH}$ from glycine's $-\text{COOH}$ combines with one hydrogen from alanine's $-\text{NH}_2$ to split off as one molecule of $\text{H}_2\text{O}$ , while the remaining carbon (from glycine's former carboxyl) and nitrogen (from alanine's former amino group) become directly bonded to each other, forming the amide linkage $-\text{CO}{-}\text{NH}{-}$ -- this specific amide bond, when it joins two amino acid units, is called the peptide bond. …

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Same / Similar Concept — real previous-year questions on the same or a closely similar concept, not this exact question.

CBSE 2026Set SEM31 markMCQ
$Q. At isoelectric point structure of glycine is$
(a) H2N-CH2-COOH
(b) H2N-CH2-COO(-)
(c) H3N(+)-CH2-COOH
(d) H3N(+)-CH2-COO(-)
›Reveal solutionSolution

At the isoelectric point an amino acid carries no net charge and exists as a zwitterion, with -COOH deprotonated and -NH2 protonated. Correct option (d).

In an amino acid the -COOH group loses a proton and the -NH2 group gains it, giving an internal salt (zwitterion). At the isoelectric point the positive and negative charges balance so the net charge is zero and the molecule does not migrate in an electric field.

…

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CBSE 2022Set ANNUAL1 markMCQ
$Q. Insulin is$
(a) an amino acid
(b) a protein
(c) a carbohydrate
(d) a lipid OR Hydrolysis of protein produces .......... number of amino acids.
(a) 15
(b) 20
(c) 25
(d) 35
›Reveal solutionSolution

Insulin is a peptide hormone made of two polypeptide chains linked by disulfide bonds, making it a protein.

Reasoning: Insulin is a hormone secreted by the beta-cells of the pancreas that regulates blood glucose levels. Structurally, it consists of two polypeptide chains (the A-chain and B-chain, made of amino acids joined by peptide bonds) held together by disulfide (-S-S-) bridges. Since it is built from amino acids linked by peptide bonds, insulin is classified biochemically as a prote …

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CBSE 2022Set ANNUAL1 markMCQ
$Q. Optically inactive compound is$
(a) Aspartic acid
(b) Lysine
(c) Cystine
(d) Glycine
›Reveal solutionSolution
Optical activity requires a chiral (asymmetric) carbon; glycine's alpha-carbon carries two identical hydrogen substituents, so it has no chiral centre and is optically inactive.

Reasoning: An amino acid's alpha-carbon is chiral (and hence the amino acid is optically active) only if it bears four different groups: -NH2, -COOH, -H, and a side chain (R group) that is different from H.

Aspartic acid, Lysine, and Cystine all have side chains different from hydrogen (a -CH2COOH, a -(CH2)4NH2, and a -CH2SSCH2- linked side chain respectively), so their alpha-carbons are genuinely chiral centres — these are optically active. …
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Q.Glycine and alanine combine to form a dipeptide. Show how the peptide bond is formed between them, and state what small molecule is released in the process.

Concept understanding — Amino Acids and the Peptide Bond

Q.Glycine and alanine combine to form a dipeptide. Show how the peptide bond is formed between them, and state what small molecule is released in the process.

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