Mod8 - DNA Mutation and Repair Flashcards
What are base tautomers?
Isomers with slightly different chemical structures to the normal bases
Describe the tautomeric shift seen in adenine (full name of normal base, tautomer, and pairing change)
Amino-adenine -> Imino-adenine
Now pairs with C, not T
Describe the tautomeric shift seen in guanine (full name of normal base, tautomer, and pairing change)
Keto-guanine-> Enol-guanine
Now pairs with T, not C
Describe the tautomeric shift seen in cystosine (full name of normal base, tautomer, and pairing change)
Amino-cytosine -> Imino-cytosine
Now pairs with A, not G
Describe the tautomeric shift seen in thymine (full name of normal base, tautomer, and pairing change)
Keto-thymine -> Enol-thymine
Now pairs with G, not A
Name the key Base Analogue (and which base is it an analogue of?)
5-Bromo Uracil (Analogue of Thymine)
What change does 5-Bromo Uracil sometimes undergo once incorporated into DNA that causes an issue?
It shifts from Keto-5bU (pairs with Adenine) to Enol-5bU (Pairs with Guanine)
Give two examples of deaminating agents
Nitrous acid and sodium bisulphite
What is Adenine deaminated to, and how does this affect its pairing?
Hypoxanthine (pairs with C, not T)
What is Guanine deaminated to, and how does this affect its pairing?
Xanthine (blocks DNA replication)
What is Cytosine deaminated to, and how does this affect its pairing?
Uracil (pairs with A, not G)
What is Thymine deaminated to, and how does this affect its pairing?
Trick Question - thymine has no amine group and thus cannot be deaminated
Name one alkylating agent and the type of mutation it causes
Ethylmethane Sulphonate (EMS) - causes a transition mutation
Name one intercalating agent
Ethidium bromide
What structural change does UV radiation cause in DNA (and what are the two types of this)?
Base dimerisation (Cyclobutyl dimers and 6-4 photoproducts)
What structural change in DNA can be caused by heat?
Hydrolysis of a ß-N glycosidic bond, resulting in an AP (apurinic/apyrymidinic) site
What enzyme can repair base dimerisations caused by UV (and in which species is it found?)
DNA Photolyase (E. coli)
Define Direct Repair
When an enzyme corrects a nucleotide alteration caused by a mutagen
Name one enzyme in E. coli and one in Humans which can reverse the effects of alkylating agents
E. coli: ADA (position 4 of T or 6 of G)
Humans: MGMT (position 6 of G)
Which enzyme carries out base excision in E. coli?
DNA Glycosylase
Which enzyme carries out nucleotide excision in E. coli (and which two parts of the enzyme actually cut the DNA)?
UvrABC Endonuclease (UvrB and UvrC)
In mismatch repair, how is the (correct) parent strand identified?
The parent strand is methylated, whereas the daughter strand is not yet
Which two enzymes are involved in mismatch repair (and which one actually cuts the DNA)?
MutS and MutH (MutH cuts the DNA)
Which proteins attract each other in non-homologous end-joining (and which enzyme actually joins the ends together)?
Ku proteins (and DNA Ligase)
In non-homologous end-joining, why are the Natural Ends of the chromosomes not joined together?
The telomeres mark the natural ends