Principles of genetic technology — common mistakes

A common pitfall is confusing the precise roles of restriction enzymes and DNA ligase. Remember: Restriction enzymes cut DNA at specific sites, often creating sticky ends, while DNA ligase joins DNA fragments together by forming phosphodiester bonds in the sugar-phosphate backbone. Be precise with your terminology and the types of bonds formed/broken.

To excel in genetic technology for 9700 Biology Paper 4, focus on understanding the detailed mechanisms of recombinant DNA, PCR, and gene sequencing, rather than just memorising steps. Practise applying your knowledge to interpret experimental scenarios and discuss ethical implications. Our premium free revision course offers comprehensive explanations and worked examples, and regularly tackling past paper questions is essential to solidify your understanding and identify common examiner expectations.

Plasmids are small, circular DNA molecules typically found in bacteria, engineered to carry relatively small genes and replicate independently within bacterial hosts. They are generally easy to manipulate. Viruses, on the other hand, are highly efficient at delivering genetic material into host cells by naturally infecting them, making them particularly useful for introducing genes into eukaryotic cells, including human gene therapy, where plasmids are often less effective.

Taq polymerase is used in PCR because it is a thermostable DNA polymerase, meaning it can withstand the extremely high temperatures (up to 96°C) required during the denaturation step of each PCR cycle without losing its enzymatic activity (denaturing itself). Most other DNA polymerases from non-thermophilic organisms would be destroyed at these temperatures, necessitating the inconvenient and costly addition of fresh enzyme in every cycle. Taq polymerase's stability makes PCR efficient and automated.