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How did we go from extracting insulin from animals to brewing pure human insulin in vats of bacteria?

Describe how recombinant DNA technology is used to produce medicines such as human insulin

A focused answer to the O-Level outcome on recombinant medicines. Making human insulin in bacteria step by step, why it beats animal insulin, and other recombinant medicines.

Generated by Claude Opus 4.89 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this dot point is asking
  2. The answer
  3. Examples in context
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What this dot point is asking

This outcome asks you to describe how recombinant DNA technology is used to make medicines, with human insulin as the central example. It pulls together everything from the genetic-engineering topics and applies it to a real, life-saving product, so a good answer is an ordered process with reasons.

The answer

Why insulin matters

People with diabetes cannot make enough insulin, the hormone that controls blood sugar, so they need a supply from outside. Before biotechnology, insulin was extracted from the pancreases of animals such as pigs and cattle.

Making human insulin in bacteria

Today, human insulin is made by genetically engineered bacteria, using the recombinant DNA process:

  1. Obtain the gene. The human insulin gene is isolated or made.
  2. Cut the gene and plasmid. A restriction enzyme cuts the gene, leaving sticky ends; the same enzyme cuts open a bacterial plasmid, giving complementary sticky ends.
  3. Join them. The sticky ends pair and DNA ligase seals them, forming a recombinant plasmid carrying the insulin gene.
  4. Transform bacteria. The recombinant plasmid is taken up by bacteria, and transformed bacteria are selected, often using a marker gene.
  5. Grow and harvest. The bacteria are cultured in large numbers in a bioreactor. As they multiply they express the gene and make human insulin, which is harvested and purified.

Why recombinant insulin is better

  • It is an exact copy of human insulin, so it is less likely to cause an allergic or immune reaction than slightly different animal insulin.
  • It gives a large, reliable, pure supply that does not depend on the availability of animal pancreases.
  • It avoids the ethical concerns some people have about using animals.

Other recombinant medicines

The same approach makes other medicines, including human growth hormone, blood-clotting factors for haemophilia, and some vaccines.

Examples in context

Example 1. From pig pancreas to pure protein. Animal insulin worked but differed slightly from human insulin and depended on a supply of animal organs. Recombinant human insulin replaced it with an identical, purer product made on demand, a landmark in medical biotechnology.

Example 2. Clotting factors for haemophilia. People with haemophilia lack a blood-clotting protein. Recombinant versions are made by engineered cells, giving a safe supply free from the infection risks once linked to products taken from donated blood.

Try this

Q1. State why people with diabetes may need insulin from outside the body. [1 mark]

  • Cue. They cannot make enough insulin themselves to control their blood sugar.

Q2. Outline the main steps to make human insulin in bacteria. [3 marks]

  • Cue. Insert the human insulin gene into a plasmid (cut with the same restriction enzyme, joined by ligase), transform and select bacteria, then grow them at scale so they express the gene and make insulin to harvest.

Q3. Give one advantage of recombinant insulin over animal insulin. [1 mark]

  • Cue. It is an exact copy of human insulin, so it is less likely to cause an allergic or immune reaction (a larger, cheaper, animal-free supply is also acceptable).

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original6 marksDescribe how human insulin is produced using genetically engineered bacteria.
Show worked answer →

Examiners want the full recombinant DNA process applied to insulin.

The human insulin gene is obtained, for example by isolating it or making it from the messenger RNA. A restriction enzyme cuts the gene, leaving sticky ends, and the same enzyme cuts open a bacterial plasmid, giving complementary sticky ends.

The gene and plasmid are mixed so the sticky ends pair, and DNA ligase seals them, forming a recombinant plasmid carrying the insulin gene. The recombinant plasmid is taken up by bacteria (transformation), and transformed bacteria are selected, often using a marker gene.

The transformed bacteria are grown in large numbers in a bioreactor with suitable nutrients, temperature and pH. As they multiply, they express the gene and produce human insulin, which is then harvested and purified.

What markers reward: obtaining the insulin gene, cutting gene and plasmid with the same restriction enzyme, joining with ligase to form recombinant DNA, transformation and selection of bacteria, and culturing at scale to express, harvest and purify the insulin.

Original4 marksExplain two advantages of insulin made by genetically engineered bacteria over insulin extracted from animals.
Show worked answer →

The answer should give two clear advantages with reasons.

First, bacterial insulin is an exact copy of human insulin, so it is less likely to cause an allergic or immune reaction than animal insulin, which differs slightly from the human form.

Second, bacteria can be grown in huge numbers quickly and cheaply, giving a large, reliable and pure supply that does not depend on the availability of animal pancreases. This also avoids ethical concerns some people have about using animals.

What markers reward: two valid advantages, such as being identical to human insulin so fewer reactions, and a larger, cheaper, more reliable and purer supply not dependent on animals.

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