Proteins can be broken down into their amino acid building blocks. Describe how proteins are digested in the human body, and explain why the amino acids produced are important.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Proteins are hydrolysed by digestive enzymes (proteases) in the stomach and small intestine. The enzymes break the peptide bonds between amino acids, producing individual amino acids. These small molecules are absorbed through the gut wall into the bloodstream. Once in circulation, the amino acids are utilised to synthesise new proteins required by the body, such as those involved in growth, repair, enzymes and structural functions.
Examiner tips
- Use the term ‘hydrolysed’ and ‘proteases’ to show understanding of the process.
- Mention the peptide bond cleavage and the production of free amino acids.
- Explain the absorption step and link it to protein synthesis.
- Show the relevance to growth, repair, enzymes and structural proteins.
Common mistakes
- Confusing digestion with absorption; failing to mention peptide bonds.
- Using vague terms like ‘break down’ instead of ‘hydrolysed by proteases’.
- Omitting the role of amino acids in synthesising new proteins.
Mark scheme (5 marks)
- Proteins are broken down / hydrolysed by enzymes (proteases / digestive enzymes)
- The peptide bonds between amino acids are broken during digestion
- Digestion produces individual amino acids (the monomers)
- Amino acids are small enough to be absorbed into the bloodstream / through the gut wall
- Amino acids are used to make new proteins needed by the body (e.g. for growth / repair / making enzymes / structural proteins)
Key terms in this question
Related
- All WJEC A-Level Chemistry (Wales) revision notes →
- How to answer a "Describe and Explain" question →
- Decode the mark scheme abbreviations →
More Amino acids, peptides and proteins questions
- Amino acids can join together to form peptides and proteins. Explain how amino a…
- Enzymes are proteins that act as biological catalysts. Explain why an enzyme sto…
- Explain how the sequence of amino acids in a protein determines its specific thr…
- Proteins are large molecules that are essential for life. Describe the structure…