Write a short note on peptide bond.

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Q. Write a short note on peptide bond.

Tamil Nadu DgeTamil Nadu HSC (DGE) Board 2024Subjective· 3mImportance★★★★★

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Concept understanding — Peptide Bond Formation

Peptide Bond Formation – From Intuition to Precision

Imagine you have two beads, each with a hole on one side and a peg on the other. To join them, you slide the peg of one bead into the hole of the next. That's the basic idea of how amino acids link up to form proteins. Each amino acid has two functional ends: an amino group ( $-\text{NH}_2$ ) on one side and a carboxyl group ( $-\text{COOH}$ ) on the other. To connect them, the carboxyl end of one amino acid must meet the amino end of another.

But there's a catch. If you just push them together, nothing happens — the peg won't fit unless you remove something that's in the way. In chemistry, that "something in the way" is a water molecule. The carboxyl group has an $-\text{OH}$ part, and the amino group has an $-\text{H}$ part. When they react, these two pieces combine to form water ( $\text{H}_2\text{O}$ ), and the remaining parts snap together to form a new bond.

That's why the process is called a dehydration-condensation reaction: "dehydration" because water is removed, and "condensation" because two molecules condense into one larger molecule.

Note

The bond that forms is called a peptide bond. It is the backbone of every protein in your body.

The Precise Statement

A peptide bond is a covalent chemical bond formed between the $\alpha$ -carboxyl group of one amino acid and the $\alpha$ -amino group of another amino acid, with the elimination of a water molecule. The reaction is:

\text{H}_2\text{N}-\text{CHR}_1-\text{COOH} + \text{H}_2\text{N}-\text{CHR}_2-\text{COOH} \longrightarrow \text{H}_2\text{N}-\text{CHR}_1-\text{CO}-\text{NH}-\text{CHR}_2-\text{COOH} + \text{H}_2\text{O}

The resulting linkage $-\text{CO}-\text{NH}-$ is the peptide bond. The two amino acids are now joined into a dipeptide.

Important

The peptide bond is a planar structure — the six atoms $\text{C}_\alpha$ , $\text{C}$ , $\text{O}$ , $\text{N}$ , $\text{H}$ , and the next $\text{C}_\alpha$ all lie in the same plane. This rigidity comes from partial double-bond character between the carbonyl carbon and the nitrogen, which prevents free rotation. This planarity is critical for protein folding.

What This Means for Proteins …

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A peptide bond is a specific amide bond formed by condensation between one amino acid's -COOH and the next amino acid's -NH $_2$ , releasing water; repeated peptide bonds link amino acid residues into peptide chains and proteins.

When two amino acids combine, the carboxyl group (-COOH) of one reacts with the amino group (-NH $_2$ ) of the other in a condensation (dehydration) reaction, eliminating a molecule of water and forming an amide linkage between the carbonyl carbon of the first and the nitrogen of the second: $H_2N-CHR_1-COOH + H_2N-CHR_2-COOH \rightarrow H_2N-CHR_1-CO-NH-CHR_2-COOH + H_2O$ The resulting $-CO-NH-$ linkage, specifically when it joins two amino acid units this way, is called a peptide bond (also called an amide bond in general organic chemistry, but 'peptide bond' is used specifically in this biochemical context). The two-amino-acid product is a dipeptide; repeating this condensation with further amino acids at either end builds up longer chains (tripeptides, polypeptides, and ultimately proteins), each successive residue linked to the next by its own peptide bond. The planarity and partial double-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 ANNUAL1 markMCQ
$Q. Which of the following bond is responsible for the linkage between two amino acids?$
(a) Peptide Bond
(b) Phosphodiester Bond
(c) Glycosidic Bond
(d) Hydrogen Bond
›Reveal solutionSolution

A peptide bond is the covalent bond that links two amino acids together, formed by removal of a water molecule.

Proteins are polymers of amino acids. Two amino acids are joined by a condensation (dehydration) reaction between the carboxyl (-COOH) group of one amino acid and the amino (-NH2) group of the adjacent amino acid, releasing one molecule of water and forming a covalent C-N bond called a peptide bond. Many amino acids linked in this way by peptide bonds form a polypeptide chain, which folds up to become a functional protein.

…

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CBSE 2024Set HALF_YEARLY1 mark
$Q. Write the answer in one sentence: What is the bond found between amino acid molecules in a protein molecule called?$
›Reveal solutionSolution

Amino acids are joined together in a protein chain by peptide bonds, formed through a dehydration (condensation) reaction between adjacent amino and carboxyl groups.

A peptide bond is a covalent amide linkage (-CO-NH-) formed when the carboxyl group of one amino acid reacts with the amino group of the next amino acid, releasing one molecule of water in the process (a condensation/dehydration reaction). Many amino acids linked in this way form a long chain called a polype …

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CBSE 2017Set ANNUAL1 mark
$Q. Write the Name of bond present between two amino acids.$
›Reveal solutionSolution
Amino acids are joined together to form proteins by a peptide bond, formed between the -COOH group of one amino acid and the -NH2 group of the next.

Each amino acid has a central carbon bearing an amino group (-NH2), a carboxyl group (-COOH), a hydrogen, and a variable side chain (R group). When two amino acids combine:

The carboxyl group (-COOH) of the first amino acid reacts with the amino group (-NH2) of the second amino acid.

This is a dehydration (condensation) reaction — a molecule of water is released, and a covalent C-N bond called a peptide bond is formed: -CO-NH- …
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Q.Write a short note on peptide bond.

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