The main properties of DNA. The genetic material must be able to: Store information Replicate (when cells divide) Express information (as proteins) Mutate at a low frequency (less than 1 in a million) DNA is a molecule that is very well suited to doing all 4 of these. Mutation.
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DNA polymerase makes about 1 mistake per 105 bp.
DNA polymerase has a “proof-reading” activity to correct its
own mistakes (99%).
After DNA replication there is a “mismatch repair” system to
correct remaining mistakes (99.9%).
This leaves an overall error rate of about 1 base in 1010.
tDNA excision repair
One strand is nicked
DNA removed between nicks
Correct DNA is synthesised
Petri dishes containing chemical to test,
liver extract, no histidine
The more mutagenic the chemical,
the more His+ colonies are produced
Number of colonies