Explain how the peptide bond is formed during translation and outline the chemical nature of this bond.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The ribosome catalyses the formation of the peptide bond between the amino group of the incoming amino acid and the carboxyl group of the growing polypeptide chain. The reaction is a condensation (dehydration) reaction, releasing one molecule of water. The peptide bond is a covalent bond between the carbon of the carbonyl group of one amino acid and the nitrogen of the amine group of the next amino acid (–CO–NH–). It has partial double‑bond character, making it planar and restricting rotation, which contributes to the regularity of secondary structures such as the α‑helix and β‑pleated sheet.
Examiner tips
- Use the word "condensation" to show the reaction type
- Specify the ribosome as the catalyst
- Mention the release of water
- Describe the bond as –CO–NH– and note its partial double‑bond character
Common mistakes
- Saying the bond is between the side chains instead of the backbone
- Forgetting to mention the ribosome or the release of water
- Describing the bond as a simple single bond without noting its partial double‑bond character
Mark scheme (4 marks)
- The ribosome catalyses the formation of the peptide bond between two amino acids / between the amino group of one amino acid and the carboxyl group of another.
- The reaction is a condensation reaction, releasing a molecule of water.
- The peptide bond is a covalent bond between the carbon of one amino acid's carbonyl group and the nitrogen of the next amino acid's amine group (–CO–NH–).
- The peptide bond has partial double-bond character / is planar, restricting rotation around the bond and contributing to the regularity of secondary structures such as the alpha-helix or beta-pleated sheet.
Key terms in this question
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
More Proteins questions
- Explain how the sequence of amino acids in a polypeptide determines the three-di…
- Explain how chaperone proteins assist in the correct folding of newly synthesise…
- Explain how fibrous proteins differ from globular proteins in terms of their str…
- Explain how post-translational modifications can alter the function of a protein…
- Explain how the amino acid sequence of a polypeptide determines the final three-…
- Explain how hydrophobic interactions and disulfide bonds each contribute to the …