Question 19M.3.sl.TZ1.8
| Date | May 2019 | Marks available | [Maximum mark: 4] | Reference code | 19M.3.sl.TZ1.8 |
| Level | sl | Paper | 3 | Time zone | TZ1 |
| Command term | Deduce, Draw | Question number | 8 | Adapted from | N/A |
Aspartame is a derivative of a dipeptide formed between two amino acids, phenylalanine (Phe) and aspartic acid (Asp).
Draw a circle around the functional group formed between the amino acids and state its name.
Name:
[2]
Name:
amide/amido/carboxamide [✔]
Note: Accept “peptide bond/linkage”.
Many candidates correctly circled the bond between the amino acid residues, though in some cases their circle missed out key atoms. Many correctly identified it as a peptide or amide linkage.
A mixture of phenylalanine and aspartic acid is separated by gel electrophoresis with a buffer of pH = 5.5.
Deduce their relative positions after electrophoresis, annotating them on the diagram. Use section 33 of the data booklet.
[2]
Phe: must be on the origin [✔]
Asp: any position on the left/anode/+ side [✔]
Most candidates seemed to realise that phenylalanine would be neutral and hence unaffected by the field, but many failed to realise that the negative charge of the aspartic acid anion would cause it to move to the left, not the right.