shows some of the advantages and disadvantages of using different organisms for the production of genetically-engineered gene products. Type of organism Advantages Disadvantages No nucleus so DNA easy to modify; have no Can’t splice introns; Prokaryotes (Bacteria) plasmids; small genome; genetics well modification; small understood; asexual so can be cloned; gene size small and fast growing; easy to grow commercially in fermenters; will use cheap carbohydrate; few ethical problems. Can splice introns; can do Do not have plasmids (except Eukaryotes modifications; can accept yeast); often diploid so two copies of large genes genes may need to be inserted; control of expression not well understood. Fungi (yeast, mould) Asexual so can be cloned; haploid, so only always make animals gene Can’t one copy needed; can be grown in vats products Plants Photosynthetic so need much Cell walls difficult to penetrate by don’t feeding; can be cloned from single cells; vector; slow growing; must be grown products can be secreted from roots or in in fields; multicellular sap. Animals (pharming) Most likely to be able to make human Multicellular; slow growing proteins; products can be secreted in milk or urine Human Insulin Insulin is a small protein hormone produced by the pancreas to regulate the blood sugar concentration. In the disease insulin-dependent diabetes the pancreas cells produce enough insulin, causing wasting don’t symptoms and eventually death. The disease can be successfully treated by injection of insulin extracted from the pancreases of slaughtered cows and pigs. However the insulin from these species has a slightly different amino acid sequence from human insulin and this can lead to immune rejection and side effects. The human insulin gene was isolated, cloned and sequenced in the 1970s, and so it became possible to insert this gene into bacteria, who could then produce human insulin in large amounts. Unfortunately it
shows some of the advantages and disadvantages of using different organisms for the production of genetically-engineered gene products. Type of organism Advantages Disadvantages Prokaryotes (Bacteria) No nucleus so DNA easy to modify; have plasmids; small genome; genetics well understood; asexual so can be cloned; small and fast growing; easy to grow commercially in fermenters; will use cheap carbohydrate; few ethical problems. Can’t splice introns; no modification; small gene size Eukaryotes Can splice introns; can do modifications; can accept large genes Do not have plasmids (except yeast); often diploid so two copies of genes may need to be inserted; control of expression not well understood. Fungi (yeast, mould) Asexual so can be cloned; haploid, so only one copy needed; can be grown in vats Can’t always make animals gene products Plants Photosynthetic so don’t need much feeding; can be cloned from single cells; products can be secreted from roots or in sap. Cell walls difficult to penetrate by vector; slow growing; must be grown in fields; multicellular Animals (pharming) Most likely to be able to make human proteins; products can be secreted in milk or urine Multicellular; slow growing Human Insulin Insulin is a small protein hormone produced by the pancreas to regulate the blood sugar concentration. In the disease insulin-dependent diabetes the pancreas cells don’t produce enough insulin, causing wasting symptoms and eventually death. The disease can be successfully treated by injection of insulin extracted from the pancreases of slaughtered cows and pigs. However the insulin from these species has a slightly different amino acid sequence from human insulin and this can lead to immune rejection and side effects. The human insulin gene was isolated, cloned and sequenced in the 1970s, and so it became possible to insert this gene into bacteria, who could then produce human insulin in large amounts. Unfortunately it