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

Hind III from Hemophilous influenzae

5’ GAATTC 3’3’ CTTAAG 5’

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

LigaseEcoRI

Sticky end Sticky end

© 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