17. 2011-02-23

Ligase seals nick in backbone d cd enzyme 1 dna

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Unformatted text preview: on • Need to review Appendix C? Ligase Seals “nick” in backbone D CD Enzyme #1 DNA polymerase base removed Enzyme #2 Phosphate-sugar removed Adds C nucleotide Insertion and deletion mutations • Example: Environmental UV radiation UV light absorbed by bases Become chemically reactive Form new abnormal bonds with each other Distorts helix Repair process leads to mutations • Repair of minor damage • Light repair • No errors no mutations • Dark repair • Only one strand damaged • Replicative template used for copying • No errors, no mutations • Repair of major damage • “SOS” repair • Mechanism complex • Both strands damaged • No intact replicative template for copying • Repair involves adding or removing small numbers of nucleotides as necessary to repair damaged region • Leads to insertion and deletion mutations The Ames Test • Detecting induced mutations in bacteria and testing for carcinogenic chemicals. • Carcinogenic chemicals are often chemical mutagens. The His operon of E. coli The Ames Test Suspension of His- Salmonella Nutrient medium Nutrient medium Spread 1 No test chemical Small amount of histidine Big colony A few 2 Test chemical Small amount of histidine Incubate Big colonies More than 1 Small colony Many Small colony Many...
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