Lesson 5 of 6 / Molecular genetics
Using bacteria to produce human insulin
How does a selected gene become a useful manufactured protein?
I can outline how an insulin-coding sequence is inserted into bacterial DNA and used in biotechnology.
I can outline bacterial production of human insulin using an introduced gene.Syllabus
Syllabus K325, Topic 12(g). Outline bacterial production of human insulin using an introduced gene.
About 5 min
Make a guess. You are not marked.
Bacteria have been engineered to make human insulin. Can the bacterial culture be injected as the medicine?
Show the answer
The insulin must be extracted and purified first.
The culture contains bacteria and other substances. Only purified, checked insulin is safe to use.
The key idea
A suitable human insulin-coding sequence can be inserted into a plasmid and introduced into bacteria. Selected bacteria are grown to produce the protein, which is recovered and purified.
A plasmid is a small circular DNA molecule separate from a bacterium's main chromosome. Restriction enzymes cut DNA at particular sequences; DNA ligase joins compatible DNA ends.
Explore the idea
From coding DNA to a purified protein
Suitable coding sequence and plasmid. Obtain a suitable insulin-coding sequence. An appropriate restriction enzyme opens the plasmid, and compatible DNA ends are prepared.
Original biotechnology outline. The orange region represents suitable insulin-coding DNA. Orange dots represent the protein product at the final stage.
Explanation
A suitable copy of the human insulin-coding DNA is obtained. It contains the information needed for the intended production system; transferring a whole human chromosome is unnecessary. A bacterial plasmid can serve as the carrier.
The plasmid is opened using an appropriate restriction enzyme, and the insulin-coding sequence is prepared with compatible ends. DNA ligase joins the sequence into the plasmid. The resulting recombinant DNA contains material brought together from different sources.
The recombinant plasmid is introduced into bacterial cells. Cells that have the intended working construct are identified and selected. Not every exposed bacterium necessarily receives the plasmid or produces the required product, so selection and checking matter.
The selected bacteria are grown under controlled conditions and use the introduced information to produce the insulin protein or a precursor that is processed as required. The product is recovered, purified and checked before medical use. This outlines the information and production pathway rather than a laboratory recipe.
Using a human coding sequence allows production of the human protein through biotechnology. This can provide a reliable manufactured supply, but safe production depends on product identity, purity and consistent quality, not just on whether bacteria grew successfully.
Step by step
- 1
Make recombinant DNA
Use appropriate cutting and joining steps to insert a suitable insulin-coding sequence into a plasmid.
- 2
Introduce and select
Transfer the plasmid into bacteria and select cells with the intended functioning construct.
- 3
Produce and purify
Grow the selected cells, recover the product and carry out the required processing, purification and quality checks.
Worked example
Cutting and joining are different jobs
A student says DNA ligase opens a plasmid and the restriction enzyme joins the insulin gene into it. Correct the roles and state the next broad stage.
One way to explain it
A restriction enzyme cuts the DNA. DNA ligase joins compatible DNA ends to form the recombinant plasmid. The recombinant plasmid is then introduced into bacterial cells, and suitable transformed cells are selected for production.
Why this answer works
- Assign cutting to the restriction enzyme.
- Assign joining to ligase.
- Continue to recipient cells rather than treating the plasmid itself as a protein factory.
Watch out for this
A student says: "Once bacteria make insulin, the whole culture can be used as the medicine." What is wrong with this?
Show the answer
The product must be recovered and purified, with any necessary processing and quality checks. Bacterial cells and other culture materials are not the finished insulin medicine.
Check your understanding
What is the plasmid's role in the insulin-production outline?
Show the answer
It carries the inserted insulin-coding sequence into bacterial cells.
The plasmid is a DNA vector. The bacteria use the introduced information in the production system.
Exam-style questions
Check your understanding
Which enzyme joins the human insulin gene into a cut plasmid?
Show the answer
DNA ligase
Ligase joins the sugar-phosphate backbones of the gene and the plasmid.
Quick recall
How does a selected gene become a useful manufactured protein?