Mutations, DNA Repair, and Recombination Flashcards
What types of mutations are transitions and transversions?
Substitutions
What is a transition?
A base substitution where a purine changes to a purine or a pyrimidine changes for a pyrimidine.
What is a transversion?
A base substitution when a purine changes to a pyrimidine or vice versa.
What is a mutation?
A heritable change in DNA sequence which can either be somatic or germline.
Which one is always larger, the forward mutation rate or the reverse mutation rate?
The forward mutation rate (there are many paths to mutation but only a single path to reversion).
What is the fluctuation test?
A test to determine whether mutations for bacterial resistance arose in response to bacteriophages or were random (spontaneous mutations that occurred prior to exposure). Since surviving colonies had very diverse population sizes, fluctuation test determined mutations were spontaneous.
What are the five types of naturally occurring spontaneous DNA damage?
Depurination, deamination, x-ray double stranded breaks, UV light producing thymine dimers, and oxidation.
What is depurination?
When the hydrolysis of water causes a purine nucleotide to detach from the DNA strand, leaving the strand with an unspecified base. This causes a mutation 3/4 of the time (1/4 chance for correct base).
What is deamination?
When the amine group of a pyrimidine detaches, changing its identity. Most commonly, the deamination of cytosine to uracil (C to U) results in a DNA change of CG to AT.
How do x-rays cause double stranded breaks?
The X-rays break the DNA backbone, splitting it in half. These DNA fragments may be ligated back together improperly leading to a mutation.
What are thymine dimers?
UV light causes adjacent Ts to form thymine dimers that lead to substitutions when DNA is replicated.
How does oxidation result in DNA damage?
The oxidation of G to 8-oxodG by a an active oxygen species (free radical oxygen) causes 8-oxodG to pair with Adenine.
What is the result of strand slippage during DNA replication?
Small insertions or deletions.
If the daughter strand slips, does it result in an insertion or deletion?
Insertion.
If the parent strand slips, does it result in an insertion or deletion?
Deletion.
Does unequal crossing over result in a mutation?
Yes, one chromosome will have a duplicated section while the other will have a deleted section.
What are transposable elements?
A DNA sequence which, upon being replicated, can move to other locations in the genome, resulting in a mutation.
What are tautomers?
Isomers of a compound that readily interconvert.
How does tautomerization lead to mutation?
Rare base tautomers do not pair correctly. For example, the rare enol form of thymine pairs with guanine. The tautomers always pair purine to pyrimidine (like A with C, not A with G).
How did Muller prove mutagens can be used to increase mutation?
Crossed bar eyed females to males who had been exposed to X-rays. Some of the offspring were bar eyed females, but all of these females carried a mutated X allele from the father. When these females were crossed to normal males, all male offspring were bar eyed, indicating a single mutated X allele as lethal (recessive lethal).
What is a mutagen?
Any physical or chemical agent that raises the frequency of mutations above the spontaneous rate.
What are base analogs?
Chemicals that are similar in structure to normal nitrogenous bases, but may have tautomeric forms that lead to improper base pairing.
Are base analogs mutagens?
Yes, they increase the frequency of mutations above the spontaneous rate.
What are hydroxylating agents?
These agents add a hydroxyl group to bases, causing them to pair improperly.
