A-LevelBiologyGenetic technology9700/41 · Oct/Nov 2024 · Q89 Marks

Scientists use many different techniques in genetic engineering.

(a)Sometimes the gene for genetic engineering cannot be extracted from the donor organism. Instead, the gene is synthesised using one of two different methods. Outline the two methods for synthesising a gene for use in genetic engineering.[3]
(b)DNA ligase and DNA polymerase are two enzymes that are used in genetic engineering. Complete Table 8.1 to show the roles of DNA ligase and DNA polymerase in genetic engineering. Use a tick (✔) if the enzyme has the role or a cross (X) if the enzyme does not have the role.[3]
(c)The polymerase chain reaction (PCR) is used to make many copies of a gene. Three temperatures are used in a PCR cycle. State the three temperatures that are used, and outline what happens at each temperature during a PCR cycle.[3]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2024). The mark or mark type is shown in brackets.

[3] any three from:
1 make cDNA from, messenger RNA / mRNA ;
2 using reverse transcriptase ;
3 synthesise (gene chemically) from nucleotides / join nucleotides ;
4 (using known) amino acid / nucleotide, sequence from database ;
[3] (table with ticks and crosses)
joins two sections of sugar phosphate backbone in DNA: DNA ligase (✔), DNA polymerase (X);
adds a gene to a plasmid: DNA ligase (✔), DNA polymerase (X);
adds free activated DNA nucleotides to a polynucleotide: DNA ligase (X), DNA polymerase (✔);
[3] 1 90-98°C - DNA, denatures / strands separate;
2 50-65°C - primers, bind / base pair / anneal (to DNA) ;
3 68-75°C – Taq / DNA, polymerase, makes, DNA / (new) strand ;

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