nounBeginner
/ˈpɛp.taɪd bɒnd/
Named by Emil Fischer, 1902 · Also called peptide linkage or amide bond
Simple Definition
A peptide bond is a covalent chemical bond (–CO–NH–) formed between the carboxyl group of one amino acid and the amino group of another, releasing a molecule of water. It is the fundamental linkage in all peptides and proteins.

Detailed Explanation

The peptide bond forms through a condensation reaction (dehydration synthesis). The –COOH group of one amino acid reacts with the –NH₂ group of the next, releasing one H₂O molecule and creating a –CO–NH– bond.

In living cells, this reaction is catalyzed by ribosomes during translation at a rate of 15–20 bonds per second. In the lab, peptide bonds are formed by solid-phase peptide synthesis (SPPS) using chemical coupling agents.

Peptide bonds have four critical properties. They are planar (six atoms lie in one plane). They have partial double-bond character (~40%) due to resonance, making them shorter (1.33 Å) than typical C–N bonds. They are almost always trans-configured. And they are kinetically stable — without enzymes, they can persist for centuries.

The reverse reaction — breaking a peptide bond — is called hydrolysis. Water is added back across the bond, catalyzed by protease enzymes like pepsin, trypsin, and chymotrypsin during digestion.

Key Facts

  • Bond energy: ~335 kJ/mol (strong covalent bond)
  • Bond length: 1.33 Å (shorter than typical C–N at 1.47 Å)
  • Formation: condensation reaction releasing H₂O
  • Breaking: hydrolysis reaction adding H₂O
  • In cells: formed by ribosomes at 15–20 bonds/second
  • In lab: formed by SPPS (Nobel Prize to Merrifield, 1984)
  • Cis form is rare (~0.03%) except before proline (~6%)

Biological Function

Peptide bonds are the structural backbone of every protein and peptide in nature. Their properties — planarity, rigidity, and hydrogen-bonding capacity — directly determine how proteins fold into alpha-helices, beta-sheets, and the three-dimensional shapes that give enzymes, antibodies, and structural proteins their function.

Example in Context

Scientific“The partial double-bond character of the peptide bond restricts rotation and forces the backbone into a planar configuration, constraining the phi and psi angles that determine protein folding.”
Everyday“Hydrolyzed collagen is made by using enzymes to break the peptide bonds in collagen protein, producing small peptide fragments your body can absorb.”

Frequently Asked Questions

A peptide bond is the chemical link that connects amino acids together in a chain. It forms when the carboxyl group of one amino acid joins with the amino group of another, releasing water.
Yes. A peptide bond is a covalent bond, meaning atoms share electrons. It has a bond energy of approximately 335 kJ/mol, making it strong and stable.
Peptide bonds are broken by hydrolysis, where water is added back across the bond. This is catalyzed by protease enzymes during digestion and protein recycling in cells.
Related Terms Peptide Amino Acid Protein Collagen

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