Genetic technology uses many different enzymes and techniques. (a) Restriction endonucleases are used in genetic modification. These enzymes occur naturally in prokaryotic cells. More than 3500 different restriction endonucleases have been identified and it is thought there are many more to discover.

Mark scheme

Marking points from the official mark scheme (May/June 2023). The mark or mark type is shown in brackets.

1. [1] Bacteria and Archaea ;
2. [4] any four from: 1 obtain (specific restriction endonuclease) gene, qualified ; e.g. gene extracted from the, DNA / genome, of E. coli / bacteria gene synthesised from the mRNA of E. coli / bacteria gene synthesised from nucleotides 2 PCR to make more copies of, gene / DNA ; 3 cut a plasmid, with a restriction enzyme / to give sticky ends ; 4 combine/mix/join, gene with plasmid using ligase ; 5 add plasmid to, E. coli / bacteria; A transformation of E. coli 6 use marker genes to, select / identify, bacteria / E. coli, with recombinant plasmids ; 7 ref. culture bacteria / use fermenter; 8 ref. extraction / purification (of enzyme); 9 AVP; e.g.heat shock / calcium ions / electroporation (detail mp5) complementary sticky ends anneal / make phosphodiester bonds (detail mp4)
3. [3] any three from: 1 (data stored is) a large amount of, amino acid / nucleotide / base / DNA, sequences ; 2 share data / access data quickly ; 3 compare (amino acid / nucleotide / base / DNA) sequences ; 4 use to, predict / visualise / model, the structure of the enzyme ; 5 identify restriction endonuclease to use or find / discover, new restriction endonucleases ;
4. [4] any four from: feature | electrophoresis | chromatography 1 separation role | both are separating techniques or both - involve movement of substances ; 2 molecule separated | DNA/RNA / proteins | pigments / named pigment/amino acids ; 3 medium | gel/named gel | paper/glass/ silica gel/named medium ; 4 separated by | (electric) current/electric field / electricity | solvent/named solvent ; 5 separated due to | charges / polarity / lengths / mass | solubilities / mass both - separate by mass ; 6 visualisation using | dyes / ethidium bromide / UV light | different colours of pigments / dyes not added / UV light not used both - dyes can be added (if TLC) ; 7 identification by | use, DNA ladder / known length of DNA or use of DNA probe | use Rf value both - use of, references / known values ;