A-LevelBiologyGenetic technology9700/41 · Oct/Nov 2019 · Q314 Marks

Therapeutic proteins are used to treat disease. The first purified therapeutic protein used was insulin, in 1922. The insulin was extracted from animal pancreases. Since 1982 most insulin has been made by recombinant DNA technology.

(a)Explain the advantages of producing human therapeutic proteins, such as insulin, by recombinant DNA technology.[4]
(b)(i)Fig. 3.1 shows the amino acid sequences of human calcitonin and calcitonin from the salmon fish, *Salmo salar*. [Figure 3.1] The two amino acid sequences shown in Fig. 3.1 can be compared. The number of amino acids that occur at the same position in both sequences can be counted and expressed as a percentage of the total number of amino acids present in one sequence. This is called the percentage sequence similarity. Use Fig. 3.1 to calculate the percentage sequence similarity of human and salmon calcitonin. Show your working. % [2][2]
(b)(ii)Compared to human calcitonin, salmon calcitonin is more biologically active. It remains active in the human body for longer and binds to calcitonin receptors more readily. Bioinformatics was used to identify this more biologically active form of calcitonin to treat osteoporosis. Explain how bioinformatics helped identify salmon calcitonin as a suitable form of calcitonin to treat human osteoporosis.[2]
(c)(i)Salmon calcitonin to treat osteoporosis is made by genetically engineered *Escherichia coli* bacteria. To produce these bacteria, a plasmid was cut and joined to the new gene to form a recombinant plasmid. The recombinant plasmid was then introduced into the bacterial cells. Name an enzyme that can: • cut plasmid DNA • join the salmon calcitonin gene with plasmid DNA.[2]
(c)(ii)Identify and explain two properties of plasmids that allow them to be used as vectors in gene cloning.[2]
(d)The gene coding for salmon calcitonin is introduced into bacteria in a specially designed plasmid called an expression vector. An expression vector must contain a prokaryotic promoter, such as the *lac* promoter. Explain why differences in the control of gene expression in prokaryotes and eukaryotes mean that expression vector plasmids must contain a prokaryotic promoter.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[4] any four from: 1 identical to human, insulin / protein ; R similar 2 no, allergic reaction / immune response / side effects; 3 human protein may, have high(er) activity / work better / (more) rapid response; 4 no chance of developing tolerance (to animal insulin); 5 no risk of transmitting diseases ; 6 supply unlimited / large-scale production ; ora not enough animal pancreases to meet demand 7 cost (of production) low(er); 8 no ethical objections / or no religious objections ; ora
[2] 16 × 100 or 100 × 16 ; 32 32 50 ; A ecf to two or three significant figures
[2] any two from: 1 (bioinformatics is) a store / database, of, base / DNA / protein / amino acid / primary, sequence data; 2 for comparison (of, database / base / DNA / protein / amino acid / primary, sequence data); 3 (to search for base / DNA / protein / amino acid / primary, sequences) similar to human calcitonin ; 4 idea of modelling / predicting, tertiary / 3D / protein, structure ; 5 AVP; e.g. sequences data pooled from all over the world
[2] restriction, enzyme / endonuclease ; (DNA) ligase;
[2] any two from: one mark if only two features stated without explanation 1 small so can be inserted (into cells); 2 replicate, independently / fast, so, high copy number/ large number of plasmids or have origin of replication so high copy number / large number of plasmids ; 3 has restriction site(s) / can be cut by restriction enzymes, so (new) gene can be added ; 4 have, multiple cloning site / polylinker, so can be cut by different restriction enzymes ; 5 have marker genes so, recombinants / transformed bacteria, can be recognised / AW ; 6 circular so stable ;
[2] any two from: 1 eukaryote and prokaryote promoter sequences are different ; 2 eukaryote and prokaryote RNA polymerase enzymes are different ; 3 prokaryotic RNA polymerase does not, recognise / bind to, eukaryotic promoter or prokaryotic RNA polymerase only binds to prokaryotic promoter ; 4 so no, transcription / mRNA made / gene expression; ora 5 eukaryotic promoter requires binding of (many) transcription factors that are not present in prokaryotic cell;