# A pharmaceutical company uses recombinant DNA technology to produce human insulin in bacteria. Explain how a gene encoding human insulin is inserted into a bacterial plasmid so that the insulin protein can be expressed.

> OCR A-Level Biology A (H420) — 6.4 Cloning and biotechnology · Explain · 4 marks

> Recombinant DNA technology allows human genes to be expressed in bacterial host cells. The process involves several molecular tools to cut and join DNA sequences, and requires careful consideration of regulatory sequences to ensure successful protein production.

## Mark scheme (4 marks)

1. The insulin gene is cut from human DNA (or produced from mRNA via reverse transcriptase) using restriction endonucleases that create sticky ends
2. The plasmid is cut with the same restriction endonuclease, producing complementary sticky ends
3. The insulin gene and plasmid are joined by DNA ligase, forming recombinant plasmid
4. A promoter sequence must be present upstream of the insulin gene so that bacterial RNA polymerase can transcribe it

## Key terms

- [recombinant DNA technology](https://www.gradenine.co.uk/glossary/recombinant-dna-technology)
- [plasmid](https://www.gradenine.co.uk/glossary/plasmid)
- [expressed](https://www.gradenine.co.uk/glossary/expressed)

## Related

- [Revision notes for OCR A-Level Biology A (H420)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-pharmaceutical-company-uses-recombinant-dna-b3e0e96f) · Published by Druglandscape Ltd.