Mutation Flashcards
(31 cards)
Suppressor mutation
genetic change that hids or suppresses the effect of another mutation
Intragenic suppressor mutation
mutation suppresses a mutation in the same gene (restoration of reading frame)
Intergenic suppressor mutation
mutation suppresses mutation in a separate gene (change the way that the mRNA is translated (encode a tRNA that adds an aa for a stop codon)
Expanding trinucleotide repeats
Repeated sequence of 3 nucleotides in which the number of the trinucleotide increases (possibly caused by hairpins which cause the template to be replicated twice – can lead to fragile X syndrome)
Bacterial gene mutation rates
10^-8 to 10^-10
Eukaryotic gene mutation rates
10^-5 to 10^-6
DNA virus mutation rates
10^-5 to 10^-6
RNA virus mutation rates
10^-3 to 10^-5
Causes of spontaneous replication errors (2)
- Tautomeric shifts (allows for alternate base pairings); 2. Wobble (flexibility in helical structure allow alternate base pairings).
Incorporated error
Mismatched base incorporated into a newly synthesized nucleotide chain
Replication error
Original incorporated error leads to a permanent error after complementary strand is synthesized
Strand slippage
Small insertions/deletions arise if one strand forms a small loop
Unequal crossing over
Misaligned pairing of homologous chromosomes results in one DNA molecule with an insertion (and the other with a deletion)
Causes of spontaneous chemical changes (2)
- Depurination (loss of a purine base from a nt and an incorrect nt is added in a newly synthesized strand); 2. Deamination (loss of an amino group, deamination of C yields U which pairs with A).
Types of chemically induced mutations (6)
- Base analogs
- Alkylating agent
- Deamination
- Hydroxylamine
- Oxidative reactions
- Intercalating agents
Base analogs (definition and how they work)
chemicals with similar structures to nt bases. DNA polymerases cannot distinguish difference so add to newly synthesized DNA, which can then cause mismatching between bases. Ex: 5BU
Alkylating agents (definition and how they work)
Add methyl and ethyl groups to bases. Akylation alters base pairing (e.g. adding an ethyl to G makes it pair with T).
Deamination (definition and how it works)
Removes an amine group from a nt base. Results in mismatch base-pairing (e.g. deaminating C results in U which pairs with C)
Hydroxylamine (definition and how it works)
Adds a hydroxyl group to cytosine. This increases the frequency of the rare C tautomer which pairs with A.
Oxidative reactions (definition and how they work)
Reactive forms of oxygen (superoxide radicals, hydroxyl radicals) are produced and damage DNA. For example, oxidation converts G into 8-oxy-7,8-dihydrodeoxyguanine which mispairs with A.
Intercalating agents (definition and how they work)
Agents that produce mutations by sandwiching themselves between adjacent bases in DNA. This distorts the 3D structure and causes single nt insertions and deletions upon replication.
How does radiation cause mutations?
Ionizing radiation dislodges electrons from atoms and can alter the structure of bases and break phosphodiester bonds. UV light is absorbed by bases and results in the creation of pyrimidine dimers (T-T most frequent) which distort the configuration of DNA and block replication
SOS system
System in bacteria that allows them to circumvent replication blocks produced by pyrimidine dimers (UV radiation). Allows bases to be inserted into a new DNA strand in the absence of bases on the template strand (results in numerous errors)
DNA polymerase eta
Found in eukaryotic cells that bypasses pyrimidine dimers (UV radiation) and inserts AA opposite the dimer. Normally works since TT dimers are most common, but error-prone since CT dimers sometimes occur.
