8. DNA repair - safeguarding the genome Flashcards
define DNA damage
chemical alterations to DNA
define a mutation
a change in base pairs
what is a subsitituation mutation
a mutation where one codon has been subsituted for another
what is a deletion mutation?
when a codon has been removed from a DNA stand and causes a frameshift mutation
what is an insertion mutation?
a mutation where a codon is inserted into a strand which causes a frameshift mutation
why dont mutations always get expressed?
because misincorporation creates a mutation on the second round of replication
what are the two types of categories of substituation mutation?
transition mutations - purine becoming purine and pyrimide becoming pyrimidine
trasversion mutations - purine becoming a pyrimidine and vice versa
how do mutations occur?
- bases that are being mimicked with slight chemical alterations and DNA polymerase dosent recognise the mutation - this is tautomerisms
- also DNA polymerase comes off the DNA strand
define a Tautomer
Tautomers are isomers of an organic compound that exist together in equilibrium and are readily interchanged by migration of an atom or group within the molecule.
why is 5-bromouracil considered a mutagen?
it resembles thymine as it has bromine at the same place as the methyl group in thymine so it can be incorporated into DNA.
forms a non-canonical base pair
what does the non canonical base pairing with 5-bromouracil result in?
the bromine is highly electronegative, therefore electrons are pulled causing the nitrogen to become a H bond receptor.
This becomes tautomerism
how can tautomerism occur within the body (without mutagens)
think of base pairing
due to the resonance strucutrues of adenine, it can result in bonding with cytosine instead of thymine.
results in tautomerism
what is deamination?
the removal of an amino group from a molecule
how does deamination create a mutated base pair?
think of a particular base pair deaminated
adenine has an amino functional group which can be deaminated therefore loosing the NH3 group, replaced with a C=O bond. this turns adenine to hypoxanthine.
this allows H bonding with cytosine
what is a compound that can increase the chance of deamination?
nitrous acid