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Lecture 34

BIOL 2030 Lecture 34: Mutagens and the Ames Test

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BIOL 2030
Herbinger Christopher

Lecture 34 - Mutagens and the Ames Test April 10, 2017 12:36 PM Mutation - permanent change in hereditary traits Mutagens  Physical mutagens o Ionizing radiation: cosmic rays, X-rays and gamma rays  High energy radiation  Comes from:  Cosmic rays - originates from the sun (presumably other stars), currently unknown events in the universe  Gamma rays: originate from radioactive decay  X-rays: emitted by electrons outside atomic nucleus  They interact with atoms and can drive off an electron - we end up with an atom that is not very stable, and is reactive  Called free radicals, and they can interact with DNA and alter the structure of bases, and break phosphodiester bonds in DNA  The more you expose cells or viruses to ionizing radiation, the more they break down o Ultraviolet radiation from sunlight  Electromagnetic radiation energy is much lower in intensity compared to ionizing radiations  Most common source is the sun (and other stars)  Can be generated by various types of lamps (e.g. mercury vapour lamps)  Pyrimidine dimers - the thymine dimers are induced by ultraviolet radiation, and become covalently linked together  Causes a kink in the double-helix  Cannot be transcribed if it is a gene  Cannot be replicated  Chemical mutagens o Base analogs: chemicals that appear similar to the normal bases in DNA but causes incorrect base-pairing and introduce point mutations during DNA replication  Something like a base, but is different, that causes point mutations  End up with base-pair substitution  5-Bromouracil: a nucleotide analog  The base looks similar to both thymine and cytosine  Is able to flip between two states to pair with adenine (common state) or become ionized to pair with guanine (uncommon state)  Mutagenic effect occurs during DNA replication  A permanent change in DNA  Transition mutation causes the change from T-A pair into C-G in 3 replication cycles o Base modifying agents: chemicals that modify groups on the normal bases in DNA that result in incorrect base-pairing during DNA replication  Modify bases, causes incorrect pairing  Only needs 2 rounds of replication  1st round c
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