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Question 23M.3.HL.TZ2.11

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Date May 2023 Marks available [Maximum mark: 5] Reference code 23M.3.HL.TZ2.11
Level HL Paper 3 Time zone TZ2
Command term Deduce, Explain, Predict Question number 11 Adapted from N/A
11.
[Maximum mark: 5]
23M.3.HL.TZ2.11

The surface antigen gene of hepatitis B virus (HBsAg) was cloned into plant cells using Agrobacterium tumefaciens. Plant cells were selected according to their resistance to kanamycin. 

Transformed plant cells were analysed by PCR to see whether they contained the HBsAg gene of 681 base pairs (bp). The image shows the resulting electrophoretic gel with lane 1 showing the reference ladder (size markers), lane 2 a positive control and lane 3 a negative control. Lanes 4 and 5 show the PCR amplification of genomic DNA from transformed plant cells.

[Source: Reprinted from Protein Expression and Purification, Vol 32, Sunil Kumar, G.B., Ganapathi, T.R., Revathi, C.J., Prasad,
K.S.N. and Bapat, V.A., Expression of hepatitis B surface antigen in tobacco cell suspension cultures, Pages 10–17,
Copyright 2003, with permission from Elsevier.]

(a)

Using the electrophoretic gel image, deduce with a reason whether the plant cell transformation was successful.

[1]

Markscheme

successful as the bands in lanes 4 and 5 are the same size as in lane 2/positive control / same size as the gene;

Examiners report

Many deduced that the transformation was successful.

(b)

Predict with a reason the DNA of the cells that could have been used as a negative control.

[1]

Markscheme

DNA from non-transformed/normal plant cells because they lack HBsAg gene/OWTTE;

Examiners report

Many deduced that DNA from a non-transformed cell was used as a control, but some forgot to mention the reason.

(c)

Explain the use of kanamycin in the selection of transformed plant cells.

[3]

Markscheme
  1. kanamycin resistance is used as a marker (gene);
  2. kanamycin kills non-transformed cells;
  3. cells are grown in a plate/medium containing kanamycin;
  4. growth indicates successful uptake (of gene)
    OR
    no growth means no uptake of gene/Ti plasmid;
Examiners report

It was difficult for most candidates to explain the use of kanamycin to select the transformed cells.