Spontaneous Mutations and their Prevention Flashcards
What are mutations?
Mutations are heritable changes to the sequences of base-pairs in DNA molecules. Most mutations are point mutations, affecting only one or two base pairs.
How can mutations arise spontaneously? (What types of mutations are there)
Mutations can be substitutions or indels (insertions and deletions) of base pairs.
These can arise spontaneously (no mutagen) through mistakes made by DNA polymerase, base slippage, and tautomerisation of base pairs.
What mechanisms do cells have to reduce the frequency of mutations?
DNA proof-reading and the Mismatch repair system.
Describe DNA proof-reading
An ability that the DNA polymerase has, allows it to check or ‘proofread’ bases it has just placed, and if an error is detected, can remove the error (via endonuclease activity) and patch the hole.
Describe the mismatch repair system
Designed to pick up mistakes that DNA polymerase may have missed. Utilises a protein complex made up MutS, MutH and MutL. MutS recognises the error, MutH detects which strand is the template strand (via methylation) and MutL facilitates the complex between the two proteins. The area surrounding the error is then degraded (exonuclease activity) and is repaired by DNA polymerase and ligase.
What is tautomerisation? and how does it increase the rate of mutations?
Tautomerisation occurs when there is a rearrangement of atoms within a single base, allowing dor non-typical base pairings to occur. The base is always transitioning between it’s tautomer and normal state, the normal state is just more favourable.
What does the Streisinger model tell us about indel mutations?
That indel mutations most frequently arise due to slippage in highly repetitive sequences of bases. Bases can ‘slip’ out and are stabilised by the surrounding bases. This results in either bases being added, or completely lost.
