Genetic_Engineering_Worksheets

Genetic_Engineering_Worksheets - Restriction Enzymes...

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Restriction Enzymes Background Information: One of the most important tools of genetic engineering is a group of special restriction enzymes ( Restriction endonucleases ). These have the ability to cut DNA molecules at very precise sequences of 4 to 8 base pairs called recognition sites . These enzymes are the “molecular scissors” that allow genetic engineers to cut up DNA in a controlled way. First isolated in 1970, these enzymes were discovered earlier in many bacteria. The purified forms of these bacterial restriction enzymes are used today as tools to cut DNA. Restriction enzymes are named according to the species they were first isolated from, followed by a number to distinguish different enzymes isolated from the same organism. It was observed that certain bacteriophages (viruses) could not infect bacteria other than their usual hosts. It was found the reason for this was that other potential hosts could destroy almost all of the phage DNA using restriction enzymes present naturally in their cells; a defense mechanism against the entry of foreign DNA. By using this molecular tool kit, of over 400 restriction enzymes recognizing about 100 recognition sites, genetic engineers can isolate, sequence, and manipulate individual genes derived from any type of organism. The sites at which the fragments of DNA are cut may result in overhanging “ sticky ends ” or non-overhanging “ blunt ends ”. Pieces may later be joined together using an enzyme called DNA ligase (molecular glue) in a process called ligation (gluing). Recognitions Sites for Selected Restriction Enzymes Enzyme Source Recognition Sites Eco RI Escherichia coli RY-13 G / A A T T C Bam HI Bacillus amyloliquefaciens H G / G A T C C Hae III Haemophilus aegyptius G G / C C Hind III Haemophilus influenzae Rd A / A G C T T Hpa I Haemophilus parainfluenzae G T T / A A C Hpa II Haemophilus parainfluenzae C C / G G Mbo I Moraxella bovis
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Genetic_Engineering_Worksheets - Restriction Enzymes...

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