| Date | May 2015 | Marks available | 1 | Reference code | 15M.3.sl.TZ2.5 |
| Level | SL | Paper | 3 | Time zone | TZ2 |
| Command term | Determine | Question number | 5 | Adapted from | N/A |
Question
Proteins are made of long chains of amino acids.
Explain how individual amino acids can be obtained from proteins for chromatographic separation.
A mixture of amino acids was spotted onto chromatography paper and eluted with a solvent mixture. The following spots were seen after the paper had been developed with ninhydrin.
Determine the \({R_{\text{f}}}\) value of the amino acid marked as X.
One protein found in the human body is collagen. Identify its function.
Markscheme
hydrolyse/break peptide bonds;
heat/boil with (concentrated) hydrochloric acid/HCl;
Accept NaOH / enzymes.
0.50;
Accept answers in the range 0.49–0.51.
Accept d/t.
structural (protein) / connective/fibrous tissue (in tendons/ligaments/cartilage/skin) / provides elasticity/strength to skin / strengthens blood vessels;
Examiners report
A large number of candidates misinterpreted the question and described in detail how the process of chromatography would separate the amino acids. Candidates who interpreted the question correctly, often did not mention that the protein had to be heated with acid and did not refer to the peptide bonds being broken in this hydrolytic process.
The \({R_{\text{f}}}\) value was often not actually calculated but the correct formula for its calculation did score the mark.
A large number of candidates misinterpreted the question and described in detail how the process of chromatography would separate the amino acids. Candidates who interpreted the question correctly, often did not mention that the protein had to be heated with acid and did not refer to the peptide bonds being broken in this hydrolytic process.
The \({R_{\text{f}}}\) value was often not actually calculated but the correct formula for its calculation did score the mark.
A large number of candidates misinterpreted the question and described in detail how the process of chromatography would separate the amino acids. Candidates who interpreted the question correctly, often did not mention that the protein had to be heated with acid and did not refer to the peptide bonds being broken in this hydrolytic process.
The \({R_{\text{f}}}\) value was often not actually calculated but the correct formula for its calculation did score the mark.
