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Date May 2022 Marks available 2 Reference code 22M.2.SL.TZ2.5
Level Standard level Paper Paper 2 Time zone Time zone 2
Command term Explain Question number 5 Adapted from N/A

Question

Enzyme activity is affected by temperature and pH.

Explain the decrease in activity of the enzyme on either side of the optimum temperature.

[2]
a.

In biotechnology, enzymes are used to transfer genes to bacteria. Outline how two specific enzymes are used for the transfer.

[2]
b.

Markscheme

  1. as temperature rises/is higher (than optimal temperature), the enzyme is denatured;
  2. as the temperature drops the enzyme molecules have less kinetic energy
    OR
    fewer successful collisions;

OWTTE

a.
  1. restriction enzymes/(restriction) endonucleases cut the gene and the bacterial/plasmid/vector DNA in the same/specific restriction sites
    OR
    (restriction) endonucleases work by targeting a specific sequence of base pairs in DNA causing both strands of the DNA to break apart;
  2. (DNA) ligase attaches/inserts the gene to the bacterial/plasmid/vector DNA
    OR
    (DNA) ligase joins the vector and gene by fusing their sugar-phosphate backbones together (with a covalent phosphodiester bond);
  3. correct reference to reverse transcriptase;

Accept correct mention of reverse transcriptase.

b.

Examiners report

In a. many incorrectly stated that the enzyme was denatured either side of the optimum. Denaturation was reasonably well known, but the explanation for increased activity with rising temperature was not. Surprisingly some candidates missed the obvious references to temperature and wrote about pH instead. Knowledge of the enzymes involved in gene transfer was very patchy, with over a quarter of candidates leaving it blank. This was the worst scoring question on the paper.

a.
[N/A]
b.

Syllabus sections

Core » Topic 2: Molecular biology » 2.5 Enzymes
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