Question 19N.3.sl.TZ0.7
| Date | November 2019 | Marks available | [Maximum mark: 4] | Reference code | 19N.3.sl.TZ0.7 |
| Level | sl | Paper | 3 | Time zone | TZ0 |
| Command term | Draw, Suggest | Question number | 7 | Adapted from | N/A |
Aspartame is formed from the two amino acids aspartic acid (Asp) and phenylalanine (Phe).
Draw the structure of the dipeptide Asp–Phe using section 33 of the data booklet.
[2]
amide link (eg, CONH) ✔
correct order and structures of amino acids ✔
NOTE: Accept a skeletal formula or a full or condensed structural formula.
Accept zwitterion form of dipeptide.
Accept CO–NH but not CO–HN for amide link.
The isoelectric point of amino acids is the intermediate pH at which an amino acid is electrically neutral.
Suggest why Asp and Phe have different isoelectric points.
[2]
«Asp isoelectric point lower than Phe and » Phe has a neutral/hydrocarbon side chain ✔
Asp side chain contains −COOH/carboxyl ✔
NOTE: Award [1 max] for “Asp has two carboxyl/−COOH groups and Phe has one carboxyl/−COOH group”.
Accept “Asp has an acidic side chain” for M2
