Topic 8-1 Flashcards
two thymine bases covalently bind and block DNA replication
pyrimidine dimer
system allows bacterial cells to bypass the replication block with a mutation prone pathway
SOS system in bacteria
in eukaryotes, the pyrimidine dimer is replaced by AA
DNA polymerase eta
what are the main types of DNA repair mechanisms for pyrimidine dimers?
- SOS system in bacteria
- DNA pol. eta in eukaryotes
high energy radiation (x-rays, gamma rays) remove electrons from atoms, altering the chemical structure of bases and inducing:
double stranded DNA breaks
UV radiation causes the formation of:
pyrimidine dimers (usually TT, but can be TC/CC)
list the six main types of chemically induced mutations:
- base analogs
- alkylating agents
- deamination
- hydroxylamine
- oxidative reactions
- intercalating agents
resembles thymine, except that it has a bromine atom in place of a methyl group on the 5C atom
5-bromouracil
a chemically induced mutation where the chemical strucutre of a molecule resembles a nucleotide base
base analogs
a chemically induced mutation where molecules add an alkyl group to normal nucleotides
alkylating agents
________ converts guanine into 8-oxy-7,8-dihydrodeoxyguanine
oxidative radicals
molecules such as proflavin, acridine orange, etc, insert themselves between adjacent bases in DNA, distorting the 3D structure of the helix - can also cause insertions and deletions which results in frameshift mutations
intercalating agents
how do we test chemicals to identify mutagens?
the Ames test is used to identify chemical mutagens
uses his- strains of bacteria to test chemicals for their ability to produce his-/his+ mutations
the Ames test
what are forward genetic screens?
identify genes that contribute to a phenotype/trait. after conducting a genetic screen, we have a collection of new mutations
what are the two main problems with forward genetic screens?
1) we don’t know if some of the same genes have been hit multiple times
2) in a genetic screen, one mutant strain may have more than one mutated gene
are crucial for the identification of new mutants
complementation tests
what is the purpose of a complementation test?
to determine whether two mutations are alleles of the same gene
‘parasitic’ DNA sequences that can move about the genome
transposable elements
movement of the transposons. may take place through a DNA or RNA intermediate.
transposition
what are the features of transposition?
- flanking direct repeats
- terminal inverted repeats
a type of transposition where a new copy of the transposable elecment inserts in a new location, and the old copy stays behind (copy and paste)
replicative transpostition
a type of transposition where the old copy excises from the old site and moves to a new site (cut and paste)
nonreplicative transposition
a type of transposition which requires reverse transcription to integrate into the target site (PDF –> copy to word doc –> print to PDF)
RNA intermediate transposition
in humans, about _____% of the human genome comprises sequences that are related to transposable elements, mostly _______
45%, retrotransposons
transposons cause mutations by:
- inserting into another gene
- promoting chromosomal rearrangements
- deleting and inserting genes as they move
IS1
simple transposable elements found in bacteria
Tn10
a composite transposon in bacteria
who was the first person to discover transposable elements?
Barbara McClintock
Ac and Ds
transposable elements in maize.
