Study Guide Lec 14 Flashcards
Define a transition mutation
base substitutions in which one purine (A or G) is changed to the other purine, or a pyrimidine (T or C) is changed to the other pyrimidine.
Define a transversion mutation
Transversions are base substitutions in which a purine is changed to a pyrimidine or vice versa.
Which mutation is more common, transition or transversion?
Although transversions would seem to be statistically favored because there are eight possible transversions and only four possible transitions, about twice as many transition mutations are actually observed in the human genome.
When and why do expanding nucleotide repeats occur?
occur when DNA insertion mutations result in an increase in the number of copies of a nucleotide repeat sequence. Such an increase in the number of copies of a nucleotide sequence may occur by errors in replication or unequal recombination.
How do expanding nucleotide repeats relate to anticipation?
Within a given family, a particular type of nucleotide repeat may increase in number from generation to subsequent generation, increasing the severity of the mutation in a process called anticipation.
A base substitution that changes the sequence and the meaning of a mRNA codon, resulting in a different amino acid being inserted into a protein, is called a ____ mutation.
missense
____ mutations occur when a mutation replaces a sense codon with a stop (or nonsense) codon.
Nonsense
A nucleotide substitution that changes the sequence of an mRNA codon, but not the meaning is called a ____ mutation.
silent
In ____ mutations, the sequence and the meaning of an mRNA codon are changed. However, the amino acid substitution has little or no effect on protein function.
neutral
____ ____ is the result of second mutations within an already mutated gene that restore a wild-type phenotype
intragenic suppression
Briefly describe two different ways in which intragenic suppressors may reverse the effects of mutations.
The suppressor mutations are located at different sites within the gene from the original mutation. One type of suppressor mutation restores the original phenotype by reverting the meaning of a previously mutated codon to that of the original codon. The suppressor mutation occurs at a different position than the first mutation, which is still present within the codon. Intragenic suppression may also occur at two different locations within the same protein. If two regions of a protein interact, a mutation in one of these regions could disrupt that interaction. The suppressor mutation in the other region would restore the interaction. Finally, a frameshift mutation due to an insertion or deletion could be suppressed by a second insertion or deletion that restores the proper reading frame.
Strand slippage that occurs during DNA replication and unequal crossover events due to misalignment at repetitive sequences have been shown to cause what?.
deletions and additions of nucleotides to DNA molecules
Strand slippage results from the formation of small loops on either the template or the newly synthesized strand. If the loop forms on the template strand, then a ___ occurs. Loops formed on the newly synthesized strand result in _____.
deletion; insertions
In regards to strand slippage, If, during crossing over, a misalignment of the two strands at repetitive sequence occurs, then the resolution of the crossover will result in what?
one DNA molecule containing an insertion and the other molecule containing a deletion.
Base analogs have structures similar to the ____ and if present, may be incorporated into the DNA during replication.
nucleotides
Many analogs have an increased tendency for ____, which can lead to mutations.
mispairing
What is required for the base analog-induced mutations to be incorporated into the DNA?
DNA replication
How do alkylating agents produce mutations? What type of mutations do they commonly cause?
Alkylating agents donate alkyl groups (either methyl or ethyl) to the nucleotide bases. The addition of the alkyl group results in mispairing of the alkylated base and typically leads to transition mutations.
How does nitrous acid produce mutations?
Nitrous acid treatment results in the deamination of cytosine, producing uracil, which pairs with adenine. During the next round of replication, a CG to AT transition will occur. The deamination of guanine by nitrous acid produces xanthine. Xanthine can pair with either cytosine or thymine. If paired with thymine, then a CG to TA transition can occur.
In regards to production of mutation, ____ works by adding a hydroxyl group to cytosine, producing hydroxylaminocytosine. The hydroxylaminocytosine has an increased tendency to undergo tautomeric shifts, which allow pairings with adenine, resulting in GC to AT transitions.
Hydroxylamine
What is the purpose of the Ames test?
The Ames test allows for rapid and inexpensive detection of mutagenic and potentially carcinogenic compounds using bacteria
In regards to the Ames test, the majority of carcinogenic compounds result in DNA damage and are mutagens. The increase in reversion rate of ___ bacteria to___ is used to detect the mutagenic potential of the compound being tested.
his–; his+
Most transposable elements have terminal ____ repeats and are flanked by short ___ repeats that are generated at insertion sites during the transposition process.
inverted; direct
Many transposable elements also contain a gene encoded one of the enzymes necessary for transposition. What are two common examples of these enzymes?
transposase or reverse transcriptase
