Gene transfer

Molecular scissors Restriction endonucleases Enzymes used by bacteria to detect and cut out viral genes Several hundred isolated Each type identifies a specific sequence of DNA Usually produce a staggered cut leaving a “sticky end” © 2010 Paul Billiet ODWS

Restriction enzymes Eco RI from Eschericia coli 5’ GAATTC 3’ 3’ CTTAAG 5’ Hind III from Hemophilous influenzae 5’ AAGCTT 3’ 3’ TTCGAA 5’ © 2010 Paul Billiet ODWS

Identifying a gene mRNA from cells making the desired protein is extracted Reverse transcriptase used to make cDNA cDNA used to make gene probes Gene located on a chromosome Gene sequenced Gene bracketed by sequences cut by a restriction enzyme Gene cut out using restriction enzyme © 2010 Paul Billiet ODWS

Plasmids Small pieces of circular DNA Found in bacteria Easily transferred from bacterium to bacterium Not necessary from the same species Useful vector for transfer of genes Insert desired gene into plasmid Insert plasmid into host cell Image Credit: Bacterial plasmid © 2010 Paul Billiet ODWS

Splicing in the gene Sticky ends permit the fragment to be “glued” into another piece of DNA cut by the same enzyme Gene Sticky end Sticky end EcoRI Ligase © 2010 Paul Billiet ODWS

Gene expression Plasmid introduced into bacterial cell Every time the bacterium divides the plasmid is replicated too Gene expressed by the bacterium Same protein is synthesised Universal genetic code Human proteins can be produced by bacteria E.g. Humulin (Human Insulin) E.g. Human somatotropin (growth hormone) © 2010 Paul Billiet ODWS