• Genetic engineering involves the manipulation of naturally occurring processes and enzymes.
• extraction/syntheses a gene(s) from one organism
• transfer gene(s) into another organism (of same or different species)
• gene is expressed in new host

Stages involved

• Obtain a copy of the required gene
• place the gene in a vector
• introducing the vector DNA into the host cell
• select the cells which have taken up the foreign DNA

Plasmids as vectors in gene cloning

• Plasmids are small, circular pieces of double-stranded DNA
• small ie they are easy to use
• exist naturally in bacteria ie bacteria take up plasmids from surroundings
• can be produced artificially
• double stranded: can insert genes from prokaryotes and eukaryotes
• replicate independently in bacteria
• can be transferred between different bacterial species

Enzymes used

• Restriction endonuclease:
• restrict viral infections by recognizing and breaking down DNA of invading viruses.
• binds to specific target site on DNA (sequence of bases) and cut sugar phosphate backbone
• straight across produce blunt ends
• staggered fashion produce sticky ends
• sticky ends: short lengths of unpaired bases; easily form hydrogen bonds with complementary base sequences on other fragments of DNA cut with the same restriction enzyme
• Reverse transcriptase:

• uses single-stranded mRNA as the template
• reverses the transcription process: produces single stranded DNA
• single-stranded DNA + DNA polymerase = double-stranded complementary DNA (cDNA)

DNA ligase links together sugar-phosphate backbones of DNA molecules and plasmid produces a closed circle of double-stranded DNA containing the new gene ie recombinant DNA