Question 21N.2.HL.TZ0.4
| Date | November 2021 | Marks available | [Maximum mark: 4] | Reference code | 21N.2.HL.TZ0.4 |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Describe, Label, Outline | Question number | 4 | Adapted from | N/A |
The figure shows a tripeptide.
Label one peptide bond in this molecule.
[1]
circle/bracket around peptide bond / arrow pointing to peptide bond / peptide bond labelled;
Allow either peptide bond
Allow if adjacent C=O and NH groups are included in the circle/bracket, but do not allow if other parts of the molecule are included.
80 % of candidates indicated one of the two peptide bonds in the diagram correctly.
Describe the secondary structure of proteins.
[2]
a. polypeptide wound into a helical structure / alpha/α helix
OR
polypeptide folded back on itself forming a pleated sheet / beta/β pleated sheet;
b. stabilized/held in shape by/due to hydrogen bonds (between C=O and N-H groups);
c. secondary structures are regular/unvarying (within polypeptides/proteins);
Allow annotated diagrams
There were some good answers here describing secondary structures and the role of hydrogen bonding.
Outline the action taken by the diaphragm during inhalation.
[1]
contracts/flattens/becomes less domed/increases volume of thorax;
80 % of candidates knew that the diaphragm contracts than relaxes during inhalation, or stated that it flattens rather than moves upwards.
