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What are mutations always seen in?
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Genotype. The genotype is changed by mutations.
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When does a spontaneous mutation arise? In what machinery is this error looked over in?
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During DNA replication. DNA polymerase III, which has proofreading function (3'-5' exonuclease activity)
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What causes induced mutations and when does it happen? Give some examples
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Exposure to certain environmental agents (mutagens). Usually occurs after DNA replication. UV light, mustand gas, ionizing radiation.
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What are mutagens?
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Substances that react chemically with DNA to modify or remove groups involved in H bonding and results in pairings of A to G, etc.
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What are the 4 types of chemical mutagens?
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UV light, Base analogs, Intercalating agents, and transposons
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What are base analogs and tautomers?
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Structurally similar to base but has an added side chain such as bromine that interferes with normal base pairing.
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What does UV light do?
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Cause adjacent thymine residues to dimerize
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What are intercalating agents? where do they bind? What is an example?
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Flat molecules that slip between base pairs. They are about the same size and shape as base pair and disrupt proper replication. They bind into the major groove of DNA.
Ethidium bromide (DNA staining dye) |
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What do thymine dimers do? How does it do this?
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Block DNA replication due to covalent bond between T residues. complementary nucleotides cannot base pair by H bonds to synthesize new strands. also interferes with transcription of mRNA if dimer is in template strand.
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What is a point mutation? What are three different kinds?
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Mutations that affect only one codon. missense, nonsense, and neutral.
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Missense mutation?
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Alter codon to specify different amino acid. may change the way a protein folds.
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Nonsense mutation?
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Alter codon to specify stop codon.
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Neutral mutation?
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Do not alter the protein product. Codon still specifies for the same amino acid even thought the codon is not exactly the same. "silent" mutation. see this in the genotype, but not phenotype.
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Frameshift mutations? what do they result from?
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Alter the reading frame and every codon after site of mutation.
result from deletion or insertion of one or more bases. |
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Back mutations or reversions? what are the 3 different kinds?
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Corrects mutation.
back, second-site, and supressor. |
