A-LevelBiologyGenetic technology9700/42 · May/June 2025 · Q512 Marks

A number of diseases in humans can be treated using recombinant human proteins. These are produced by recombinant DNA technology.

(a)To produce a human protein for treatment of a disease, recombinant DNA technology needs a gene coding for the particular human protein. Outline the different ways that can be used to obtain a gene that codes for a human protein.[4]
(b)Diabetes mellitus is a disease in which the blood glucose concentration cannot be controlled. Many people with diabetes mellitus use recombinant human insulin to help control their blood glucose concentration. Before recombinant human insulin became available, animals were the main source of insulin. Explain the advantages of using recombinant human insulin to treat diabetes.[3]
(c)Explain why the DNA involved in the production of recombinant human insulin is termed recombinant DNA.[1]
(d)Recombinant human insulin analogues are insulin proteins that have slightly altered amino acid sequences compared with recombinant human insulin. These analogues can be more effective than human insulin. Synthetic genes coding for insulin analogues have been developed. The bacterium Escherichia coli can be used as a host for a synthetic gene for the large-scale manufacture of an analogue. When scientists have determined the changes that are needed to produce an insulin analogue, they can obtain a synthetic gene coding for the analogue by making changes to a length of DNA using genetic engineering. Suggest how scientists genetically engineer a synthetic gene coding for the insulin analogue and explain how the changes they make allow the correct analogue to be produced.[4]

Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[4] (a) any four from: 1 find, nucleotide / base / gene / DNA, sequence ; 2 from database / using bioinformatics / from gene library; 3 make the gene (chemically) using nucleotides ; 4 extract mRNA from cell, making the protein / expressing the gene ; 5 use reverse transcriptase (with mRNA) to make cDNA ; 6 use DNA polymerase (with cDNA) to make dsDNA ; 7 cut out / extract / isolate, the gene from DNA ; 8 using restriction enzyme ;
[3] (b) any three from: ora for animal insulin 1 large scale supply / supply can match demand ; 2 no / less, likely to cause, immune / allergic, response or fewer side-effects; 3 faster to act / smaller dose needed ; 4 no / less, likely for (insulin) tolerance to occur; 5 no / less, risk of infection / disease; 6 no / less, ethical / religious objections or suitable for, vegetarians / vegans; 7 AVP; e.g. cheaper to produce / easier to purify
[1] (c) DNA from two different sources (joined together) or DNA from (human) gene joined to DNA from, bacteria / plasmid ;
[4] (d) any four from: 1 find, nucleotide / base / gene / DNA, sequence (of human insulin gene); 2 from database / using bioinformatics / from gene library; 3 gene editing; 4 insertion / deletion / replacement, of nucleotide(s) ; 5. at specific sites (of the gene); 6 (results in) changes to the, (DNA) triplet / codon; 7 (so codes for a) different amino acid ; 8 AVP; e.g. detail of gene editing / CRISPR/Cas9