International A Level Biology / Gene technology
Drugs from genetically modified organisms revision notes
Edexcel International A Level Biology (YBI11), chapter 25: Gene technology, specification point 8.17. Free lesson.
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Genetically modified microorganisms, plants and animals can make useful protein drugs. The host organism must be chosen to suit the protein, especially if it needs changes that bacteria cannot make.
How bacteria make human insulin
Human insulin has two polypeptide chains, called A and B. In the classic method, each chain is made separately using its own gene. The chains are then purified and joined by disulfide bonds to form working insulin. Each gene is put into a plasmid using restriction endonucleases and DNA ligase. Each plasmid also has a marker gene. The plasmids are transferred into E. coli using calcium ions and a heat shock. The marker gene helps identify transformed bacteria. These bacteria are grown in fermenters, then the A and B chains are extracted and purified. Later methods use one gene for…
Why GM insulin is useful
GM insulin is identical to human insulin, unlike pig insulin, which differs by one amino acid. This makes an immune response less likely. It can also be made in large amounts, and some people object to using pig insulin. When asked for advantages of GM insulin, describe the insulin, not how quickly the bacteria grow or how easy they are to keep.
How goats make antithrombin in milk
Pharming means using farm animals to make a drug. Human antithrombin is a blood protein that stops blood clotting too easily. A human antithrombin gene is joined to a goat milk protein promoter, which switches the gene on in the mammary glands. The gene is human. Only the promoter comes from the goat.
Why some drugs need a eukaryotic host
Many human proteins need post-translational modification, meaning changes made after translation. In eukaryotic cells, the rough ER and Golgi apparatus can add carbohydrate chains to proteins. This makes a glycoprotein. Bacteria are prokaryotes and have neither structure, so they cannot make glycoproteins. They may also fold large, complex proteins incorrectly, changing their shape and stopping them from working. Bacteria suit simpler proteins such as insulin, which has no carbohydrate attached. Antithrombin is a glycoprotein, so goat cells can make a functional form but bacteria…
Comparing microorganisms, plants and animals
Each system has different strengths. Choose one that can make the protein in the form needed, rather than giving general advantages of genetic modification. Microorganisms: E. coli can make insulin. Genes are put in using plasmids and heat shock. Growth in fermenters is fast and cheap, but bacteria cannot add carbohydrate. Plants: tobacco leaves can make antibodies. Genes can be transferred using Agrobacterium or a gene gun. Plants are cheap to grow in bulk and are eukaryotic, but their sugar groups can differ slightly from human ones. Animals: goats can make antithrombin in milk.…