Exam 16: Mutation, Repair, and Recombination

Shown below is a list of statements (a-k)and types of mutations (1-6).On the blank line following each mutation,write the letter(s)of all statements that apply to that type of mutation.Note that each statement may be used more than once and each type of mutation may have more than one correct statement. a)a mutation that changes UUA to UUG b)a mutation that gives methionine instead of leucine c)created by the addition of a nucleotide to a coding region d)a stop codon is read as an amino acid e)a chemically similar amino acid is replaced by the mutation f)a mutation that changes CCU to ACU g)da nucleotide in a coding region gives this type of mutation h)mutation does not alter the peptide i)a mutation changing UAU to UAG j)premature termination codon is responsible for this mutation k)a chemically different amino acid is replaced by the mutation 1)missense mutation __________ 2)silent mutation __________ 3)frameshift mutation __________ 4)nonsense mutation __________ 5)synonymous mutation __________ 6)nonsense suppressor mutation __________

A mutation that occurred in a plant petal would be best termed:

Some indel mutations can be created spontaneously as a result of errors during DNA replication. a)Use diagrams to show how 1)insertions and 2)deletions are spontaneously created as a result of the replication of tandem repeats. b)Give the term used to describe this process. c)Name two human diseases that arise as a consequence of expanded trinucleotide repeats in DNA. d)Describe two ways in which expanded trinucleotide repeats can cause disease.

Below are a list of mutagen mechanism descriptions (a-e)and a list of mutagen names (1-5).On the blank line following each mutagen,write the letter(s)of all descriptions that apply to that type of mutagen.Note that each statement may be used more than once and each type of mutation may have more than one correct statement. a)Single-nucleotide insertions or deletions resulting in frameshift mutations if the mutation occurred in the coding region.The mutagen is a flat planar molecule that slips between stacked nitrogen bases. b)Causes transitions (usually GC to AT)by adding an alkyl group to a base (usuallyG),thus altering its pairing properties. c)Causes AT to GC transitions by acting as a base analogue for adenine.It is unstable and readily undergoes tautomeric shifts.Its imino form pairs with C rather than G. d)Causes GC to TA transversions.Creates an apurinic site by breaking the base-sugar bonds.In order to correct the mutation,the SOS repair system preferentially adds an A opposite to G. e)Makes pyrimidine dimers by making a bond between adjacent pyrimidines,thus interfering with the normal base pairing between the complementary DNA strands. 1)2-aminopurine __________ 2)UV light __________ 3)acridine orange __________ 4)aflatoxin __________ 5)ethylmethanesulfonate (EMS)__________

After mutagen treatment,a molecule of 2-aminopurine (an adenine analogue)incorporates into DNA.During replication,the 2-AP protonates.The mutational event caused by this will be:

5-Bromouracil is an analog of thymine that normally pairs with adenine.Its rare tautomeric form pairs with adenine.Show the steps (i.e.,several replications)by which 5-bromouracil causes the GC base pair shown below to change to an AT base pair.Show the point at which the rare tautomeric form of 5-bromouracil occurs.Show both products of all divisions in which 5-bromouracil is involved.Do not show chemical structures.

E.coli cells that have null mutations in the gene encoding mutH will be defective in:

Proto-oncogenes are genes that:

In a haploid fungus,a small in-frame deletion arises in the coding region of a gene necessary for the production of the amino acid leucine.The deletion removes the three base pairs corresponding to a UAC codon (encoding cysteine).This small deletion will most likely cause:

In E.coli,a region of a gene with repeats of the sequence CTGG will be prone to:

In E.coli,a region flanked by two repeats of a sequence such as GTGGTGAA is prone to:

Crossing over is a very precise process.Why is it important that the process of crossing over is so precise? What impact would there be if it were not precise? Draw a picture depicting an imprecise crossover and show the result of this imprecise event.

a)A met⁺ strain of Neurospora was treated with a mutagen to create met^- mutants.The mutants were reverted to met⁺ with HA (hydroxylamine),which causes GC to AT transitions.What was the original mutation on the molecular level? b)Two of the revertants showed odd results when crossed with a wild-type met⁺ strain. Cross Progeny revertant A \timesme wild type 88\% 12\% revertant B \times wild type 93\% 7\% Explain how these results occurred and why the above numbers of offspring were obtained.

A mutation that changes the codon UAA to the codon UAG in a mammalian cell line is called a(n):

The spontaneous reversion rate for a chemically induced mutation is 1 × 10^-8.For EMS ,the rate is 0.9 × 10^-8,and for acridine,it is 2 × 10^-5.What change was involved in the original mutation?

Imagine that exposure to the antibiotic streptomycin promotes mutations causing streptomycin resistance in E.coli.If you repeated Luria and Delbruck's test using streptomycin instead of the T1 phage,what results would you expect?

A mutation does not affect the length of a gene but results in an abnormally short protein.The mutation is most likely of a type called:

Photoreactivation repair is effective only in the presence of visible light.What other repair mechanism is available to repair pyrimidine dimers if visible light was not available? Describe the steps of this mechanism.

The Ames test is used for determining whether a particular chemical acts as a mutagen.It does this by selecting for:

Consider the following mutations and,for each,explain whether you expect it to be a)potentially promoting cancer b)dominant or recessive i)a mutation that destroys the active site of an enzyme necessary to promote cell cycle ii)a very premature STOP codon in a gene encoding a protein involved in the excision-repair mechanism iii)a point mutation that renders constitutively active one of the signaling proteins in the Ras pathway iv)a null mutation in a gene encoding an apoptotic (apoptosis-promoting)protein