Lecture 16 - Causes of DNA mutation Flashcards
What is a mutation?
An alteration in the nucleotide sequence of a DNA molecule
What are the two ways mutations can occru?
Errors in DNA replication, spontaneous mutation
Mutagens
What is a mutagen?
Chemical or environmental agents that cause changes in DNA molecules
How does an error in replication result in a mutation?
If one base is replicated incorrectly, when the next replication occurs the complementary base to this incorrect base will be different also
This increases the scale of the mutation
What is the cause of errors in DNA replication or spontaneous mutations?
Mistakes being made by DNA polymerase
What is a tautomer?
An isomer with a slightly different chemical structure
What is base tautomerism?
DNA polymerase is tricked due to tautomers
It can’t tell the difference between two isomers and instead may place the incorrect one in
This causes tautomeric shift and the wrong amino acid is used
What are the two ways that mutagens can cause mutations?
Base analogs
Direct structural change
What is meant by base analogs?
Chemicals that look like bases are incorporated instead of bases
What is an example of a base analog causing a mutation?
5bU is an analog of thymine and may be placed into sequence
Usually this is no problem
However there is an enol tautomer of 5bU that pairs with G which can cause tautomeric shift
What is direct structural change?
Deaminating agents change the structure of some nucleotides
What are some effects of deaminating agents?
Deamination of adenine gives hypoxanthine which pairs with C not T
Deamination of cytosine gives uracil, which pairs with A not G
Deamination of guanine gives xanthine which blocks DNA replication
What are some other agents that cause structural changes to nucleotides?
Alkylating agents which add alkyl groups
Intercalating agents which insert between base pairs
Ultraviolet radiation which causes base dimerisation
Heat which causes detachment of bases and gives rise to an AP site
