Manufacturing Human Insulin

Section 1 of 6Making insulin by genetic engineering

1

Locate the gene for insulin on a human chromosome.

2

Cut the gene out using a restriction enzyme. The enzyme leaves short stretches of unpaired bases called sticky ends.

3

Cut open a bacterial plasmid, a small ring of DNA, with the same restriction enzyme so that it has matching sticky ends.

4

Mix the gene with the plasmids. DNA ligase joins the sticky ends together, forming a recombinant plasmid.

5

Insert the recombinant plasmid into bacterial cells.

6

Grow the bacteria in a fermenter. As they divide, the plasmid is copied and every new cell contains the insulin gene.

7

The bacteria make human insulin, which is collected and purified for use by people with diabetes.

Section 2 of 6The tools used

Tool	Role
Restriction enzyme	Cuts DNA at a specific sequence, leaving sticky ends
DNA ligase	Joins DNA pieces with matching sticky ends into one molecule
Plasmid (vector)	Carries the gene into the bacterial cell and is copied when the bacterium divides
Fermenter	Provides controlled conditions for rapid growth of large numbers of bacteria

Section 3 of 6Why this is better than the older method

Source of insulin

• Source of insulin Insulin used to be extracted from the pancreases of pigs and cattle,
  • which gave a protein slightly different from human insulin and was limited by how many animals were available.

Genetically engineered insulin

• Genetically engineered insulin The bacteria make exactly the human form of the protein,
  • so it works well in the patient and is unlikely to cause an immune response.
• Production can be scaled up in fermenters to meet the demand from the growing number of people with diabetes.

Section 4 of 6Why bacteria are ideal

Use of bacteria

Same genetic code

• Same genetic code All organisms use the same genetic code, so bacteria can read the human gene and make the same protein.

Plasmids

• Plasmids Plasmids are separate from the main chromosome and easy to remove, alter and put back.

Fast reproduction

• Fast reproduction Bacteria multiply rapidly, giving a large amount of insulin in a short time.

Few ethical concerns

• Few ethical concerns Unlike animals, bacteria cannot feel pain or distress, so there are fewer ethical objections.

Section 5 of 6Key terms

Term	Meaning
Genetic engineering	Transferring a gene from one organism into another so it makes a new protein.
Restriction enzyme	An enzyme that cuts DNA at specific base sequences.
Sticky ends	Short unpaired sections of DNA left by a cut that can join to matching ends.
DNA ligase	An enzyme that joins pieces of DNA together.
Recombinant plasmid	A plasmid containing a gene from another organism.
Plasmid	A small circular piece of DNA found in bacteria.

Section 6 of 6Exam technique

1

Mixing up the two enzymesrestriction enzymes cut, ligase joins.

2

Saying the plasmid is cut by a different enzyme from the gene — the same one must be used so the sticky ends match.

3

Writing that bacteria are cut open to insert the gene — the gene goes in via the plasmid.

4

Saying insulin comes from the bacteria's own DNA — the gene is human; the bacteria only copy and express it.