Recombinant DNA technology involves the transfer of fragments of DNA from…

The idea

Recombinant DNA is DNA made by joining together DNA from two different organisms, usually from different species. The sequence of operations is fixed and worth learning as a whole. The required gene is isolated - cut out with restriction endonucleases, made from mRNA using reverse transcriptase, or built in a gene machine. Promoter and terminator regions are added so that the host's RNA polymerase knows where to start and stop. The fragment is inserted into a vector, normally a plasmid or a virus, using the same restriction enzyme to create complementary sticky ends and DNA ligase to seal the sugar-phosphate backbones. The vector carries the DNA into a host cell; a cell that takes it up is transformed, and a whole organism containing DNA from another species is transgenic.

What earns the marks

• Recombinant DNA being DNA from two different organisms or species joined together.
• The fragment being isolated by a named method before transfer.
• The fragment being inserted into a vector such as a plasmid or a virus.
• The vector carrying the DNA into the host cell, which is then described as transformed or transgenic.
• A named useful product, such as a human protein produced by bacteria or by a genetically modified animal.

Common mistakes and how to put them right

• Calling the recipient organism 'genetically mutated' instead of transformed or transgenic.

• Describing the gene as injected straight into a bacterium with no vector at all.

• Confusing the vector with the host cell, so calling the bacterium the vector.

• Writing that the bacteria 'make the gene' rather than the protein for which the gene codes.

• Leaving out promoter and terminator regions, so nothing explains how the gene is expressed.

Exam tips

• Learn the sequence as five steps - isolate, add promoter and terminator, insert into vector, transform, culture - and you can answer almost any version of this question.
• Use 'transformed' for cells and 'transgenic' for whole organisms; the terms are marked separately.
• Name the product and the host when you can; a specific example often carries the final mark.