Describe how the polymerase chain reaction is used to clone and amplify DNA.

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

1. [1] DNA denatured / ssDNA produced ;
2. [1] by heating to, 94 / 95 °C ;
3. [1] add primer (DNA) ;
4. [1] complementary base pairing (with sample DNA);
5. [1] at 55-65 °C;
6. [1] ref. to annealing;
7. [1] DNA polymerase builds new strands / AW ;
8. [1] by adding free nucleotides;
9. [1] at 70-75 °C;
10. [1] ref. to Taq polymerase thermostable ;
11. [1] does not need replacing ;
12. [1] new strand denatured and process repeated;
13. [1] process is automated;
14. [1] can produce large(r) quantities ;
15. [1] use bacterial host / hamster cell host / insect larva cell;
16. [1] product exactly the same as human protein ;
17. [1] (as) product has same amino acid sequence
18. [1] no immune response ;
19. [1] no side effects ;
20. [1] no risk of transfer of disease ;
21. [1] easier to obtain purified product;