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Date November 2021 Marks available 2 Reference code 21N.2.HL.TZ0.4
Level Higher level Paper Paper 2 Time zone TZ0 / no time zone
Command term Describe Question number 4 Adapted from N/A

Question

The figure shows a tripeptide.

Label one peptide bond in this molecule.

[1]
a.

Describe the secondary structure of proteins.

[2]
b.

Outline the action taken by the diaphragm during inhalation.

[1]
c.

Markscheme

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.

a.

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

b.

contracts/flattens/becomes less domed/increases volume of thorax;

c.

Examiners report

80 % of candidates indicated one of the two peptide bonds in the diagram correctly.

a.

There were some good answers here describing secondary structures and the role of hydrogen bonding.

b.

80 % of candidates knew that the diaphragm contracts than relaxes during inhalation, or stated that it flattens rather than moves upwards.

c.

Syllabus sections

Additional higher level » Topic 7: Nucleic acids » 7.3 Translation
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Additional higher level » Topic 7: Nucleic acids
Additional higher level

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