Draw a circle around the functional group formed between the amino acids and state its name.

Name:

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.

Aspartic acid is obtained synthetically as a racemic mixture. Draw the three‑dimensional shape of each isomer showing their spatial relationship to each other. Use section 33 of the data booklet.

Name:
amide/amido/carboxamide    [✔]

Note: Accept “peptide bond/linkage”.

Phe: must be on the origin    [✔]

Asp: any position on the left/anode/+ side    [✔]

    [✔]

Candidates were challenged to draw a circle around the functional group formed between the two amino acids in a dipeptide. Commonly the central C=O or the N-H groups were circled instead of the amide. Some candidates then named the functional group as a ketone or amine, however most candidates stated “peptide” here and scored a mark.

Most candidates correctly deduced the positions of the two amino acids after electrophoresis.

Was very poorly answered. Many candidates had difficulty drawing a 3D structure and showing the spatial relationship of two enantiomers. An incorrect amino acid residue was often used, or incorrect bond connections drawn.