Lecture 14 - Genetic Mutations

Mutation

a heritable change in the DNA

a change in DNA sequence

Result ini mutant organism

may have a different phenotype in comparison with the wild type

Point mutation

change in a single nucleotide position

Substitution

one or more bases are replaced by the same number of bases

Insertion

(addition) one nor more bases

Inversion

DNA is flipped in orientation

Deletion

(removing) one or more bases

True reversion

DNA mutates back to original sequence

Silent mutation

DNA change does not change the amino acids or function of the protein

Missense mutation

changes the amino acid to another - can effect enzyme function ±/-

Conditional mutation

Only apparent under certain conditions

Reversion mutation

a true reversion or suppressor mutation reverts the protein to its original function

nonsense mutation

changes the amino acid sequence to a stop codon

frameshift mutation

changes the open-reading frame. Occurs with insertion/deletion of nucleotides not divisible by 3

in-frame mutation

does not change the open-reading frame. Occurs with insertion/deletion of nucleotides divisible by 3

Spontaneous mutation

typically a mistake in DNA replication that later affects transcription and translation

Induced mutation

exposure of DNA to a mutagen

Mutagens

Chemicals or radiation that increase rate of mutation.

Ionizing

X-rays and gamma rays: break the DNA

Non-ionizing

Ultraviolet rays: form thymine dimers

DNA Repair

How cells repair mistakes to minimize mutations

Proofreading

DNA Pol double checks new uses to make sure its a match

Mismatch repair

Sometimes DNA Pol Misses and another set of enzymes check after replication machine moves

Nucleotide excision repair

removes a set of nucleotides upstream and downstream a thymine dimer. Then DNA pol I and DNA ligase come and fill in the gap.

Ames Test

A test of mutagenicity of a substance (typically chemical) - particularly for humans

Uses Salmonella with mutation in hisG needed for
histidine synthesis

This means the bacteria cannot grow on media
lacking histidine (amino acid)

You can test for mutation (revertants) in the
presence of the mutagen

Mutagenicity of chemicals processed by the liver

Chief detoxifying organ of the human body
Chemically modify foreign substances. Can metabolize them into mutagens