Exam 16: Mutation, Repair, and Recombination

Which of the following mutations is/are MOST likely to result in cell overgrowth and (eventually)may lead to cancer?

If an incorrect base is incorporated during DNA synthesis and is not corrected by DNA polymerase,it can be corrected by postreplication repair.Postreplication repair does NOT involve which of the following?

E.coli cells that have null mutations in the gene encoding adenine methylase will have:

A missense mutation in Neurospora will revert by treatment with nitrous acid,but not by hydroxylamine.Hydroxylamine (HA)causes only G·C → A·T transitions,while nitrous acid causes both G·C → A·T and A·T → G·C transitions.The original mutation (not the reversion)must have been:

Shown below is a list of types of repair systems or repair molecules (a-g)and types of DNA damage or mutations (1-5).On the blank line following each type of damage,write the letter(s)of all repair systems that can repair (or play a role in the repair of)that particular type of damage. a)photolyase b)base-excision repair c)SOS repair d)alkyltransferases e)mismatch repair f)homologous recombination g)nucleotide-excision repair 1)alkylation of G residues __________ 2)depurination __________ 3)pyrimidine dimers __________ 4)deamination __________ 5)double-stranded breaks __________

Five different mutations were derived from base pair substitutions at a single codon.In this codon,the mutant alleles had arginine,leucine,glycine,serine,and cysteine.What was the wild-type codon?

In E.coli,mutations arising during repair are mostly caused by:

Fragile X syndrome is caused by:

The fluctuation test of Luria and Delbruck showed that:

The Spo11 enzyme in eukaryotic cells makes:

A mutant plant with white flowers exists that lacks red anthocyanin pigment,normally made by enzyme P.Indeed the petal tissue lacks all detectable activity for enzyme P.Despite the lack of enzyme activity,a study of homozygous mutant cells using antibodies against the wild-type enzyme demonstrated that the cells homozygous for the mutation still had the enzyme (i.e.,the antibody showed the presence of the enzyme).Which statement could explain these results?

How do mutation and DNA damage differ?

Both cytosines and 5' methyl-cytosines are susceptible to spontaneous deamination,which leads to GT to AT transitions.Do you expect cytosine nucleotides to be a "hot spot" for spontaneous mutations? Briefly explain your answer.

Which of the following diseases is/are MOST likely to be caused by excessive exposure to UV light?

A partial peptide sequence for the wild type and three mutant alleles of a gene,PET1,are shown below.Each mutant was caused by a single point mutation. $\text { Wild type:\quad met \quad ile \quad arg \quad met \quad asp \quad lys \quad trp... }$ $\text { Mutant 1:\quad met \quad ile \quad gln \quad asn \quad gly ... }$ $\text {Mutant 2:\quad met \quad ile \quad arg \quad met \quad gly \quad lys \quad trp...}$ $\text {Mutant 3: \quad met \quad ile \quad ser \quad met \quad asp \quad lys \quad trp...}$ a)Using the amino acid sequence of the wild type and the three mutants,deduce the exact DNA sequence of the coding strand of the wild-type allele. b)What type of mutation (transition vs.transversion vs.indel;missense vs.nonsense vs.frameshift)has occurred in each mutant? c)What consequence will each of the above-mentioned DNA mutations have on protein function?

In a haploid fungus,a transversion arises in the coding region of a gene necessary for the production of the amino acid leucine.The transversion substitutes the last base in the codon UAC (encoding cysteine),resulting in the stop codon UAG.This substitution will most likely cause:

Which of the following diseases is/are LEAST likely to be caused by excessive exposure to UV light?