Interferon-alpha (IFN-α) can be produced as a recombinant human protein to treat some types of cancer. The gene IFNA2 codes for IFN-α. One method of producing recombinant IFN-α uses genetically engineered Escherichia coli bacteria that contain recombinant plasmids. Each recombinant plasmid contains: • the gene IFNA2 • three regulatory sequences of the lac operon (promoter, operator and lacl) • a gene for antibiotic resistance, AMPR. Each of the sequences for the lacl gene and AMPR gene contains its own promoter. As a result, these genes are always expressed in E. coli bacteria that contain this recombinant plasmid. Fig. 2.1 is a diagram of the recombinant plasmid. The promoter regions of the lacl gene and AMPR gene are not shown. [Figure 2.1]

Mark scheme

Marking points from the official mark scheme (Feb/Mar 2023). The mark or mark type is shown in brackets.

1. [2] (a)(i) 1 is regulatory gene / codes for repressor (protein) ; R is a transcription factor R lacl is a repressor protein
2. [2] (a)(i) 2 prevents, transcription/RNA polymerase binding to promoter ;
3. [3] (a)(ii) any three from: concentration of IFN-α produced
4. [3] (a)(ii) 1 increases steeply (after addition of IPTG);
5. [3] (a)(ii) 2 peak is, at 8 hours / 4 hours (after addition of IPTG);
6. [3] (a)(ii) 3 decrease is less steep or final concentration greater than starting concentration / AW ;
7. [3] (a)(ii) 4 data quote ;
8. [1] (a)(iii) any one from: IPTG is higher / lactose is lower, because
9. [1] (a)(iii) 1 lactose has to be converted to allolactose ;
10. [1] (a)(iii) 2 lactose is broken down so needs to be continually taken up or IPTG is not broken down so continually binds to repressor ;
11. [1] (a)(iii) 3 IPTG will be at higher concentration than allolactose ; A lactose for allolactose
12. [1] (a)(iii) 4 IPTG has higher affinity for repressor protein than allolactose ; A lactose for allolactose
13. [1] (a)(iii) 5 lactose, used up / concentration decreases ;
14. [1] (a)(iii) 6 more IPTG enters ;
15. [1] (a)(iv) IFN-α is, unstable / breaks down ;
16. [1] (b) (only E. coli that have taken up the plasmid) will, grow / survive, in the presence of, ampicillin / antibiotic ;
17. [5] (c) any five from:
18. [5] (c) 1 (random) mutation;
19. [5] (c) 2 natural selection / directional selection;
20. [5] (c) 3 antibiotic acts as selection pressure / AW ;
21. [5] (c) 4 bacteria with mutation, have selective advantage / survive / reproduce or bacteria with, gene / allele, that codes for antibiotic resistance, have selective advantage / survive / reproduce ;
22. [5] (c) 5 pass on, mutation / gene / allele, (for antibiotic resistance) by, binary fission / asexual reproduction / vertical transmission;
23. [5] (c) 6 pass on, mutation / gene / allele, (for antibiotic resistance) by, transduction / transformation / conjugation / horizontal transmission ;
24. [5] (c) 7 AVP; e.g. increased chance of resistance if people do not finish full course of antibiotics overuse of antibiotics some antibiotics may act as mutagens