SB ch 7 sec 1-2

The removal of a purine from DNA is called:

Depurination

Which of the following statements accurately describes the relationship between DNA replication and mutation?

Even though DNA replication is very accurate, it can introduce errors, typically, less than once in every 109 base pairs.

In the Ames test for mutagenicity, the control sample contains what?

Rat liver extract + Salmonella bacteria that cannot synthesize histidine

Assume thymine was in its rare tautomeric state when DNA polymerase used it as a template during replication. After a second round of replication, the result would be a _____.

TA to CG mutation in one of the four daughter molecules

Which of these tests is used to evaluate the mutagenicity of an agent?

The Ames test

What accounts for the low error rate in DNA replication?

The polymerase has a 3'-to-5' exonuclease.

Why are mutations in somatic cells important?

They can affect genes that regulate cell growth and division and therefore cause cancer.

Why is rat liver extract added to the chemical under analysis in a typical Ames test?

To simulate the effect of mammalian metabolism on the agent test for mutagenicity

The organism used in the Ames test is _____.

a bacterium

A base tautomerization usually leads to a(n) _____.

a base substitution

Replica plating is a technique in which ______.

bacterial colonies are transferred from one plate to another with a sterile piece of velvet cloth

Which of these mutations changes a mutant allele back to a wild-type allele?

reversion

a ________ mutation is one that converts a mutant allele back to the wild-type form.

reversion

A base substitution in which a purine and a pyrimidine are interchanged is called a(n) _________ mutation.

transversion

A base substitution in which a purine and a pyrimidine are interchanged is called a(n) __________ mutation.

transversion

Thymine dimers are typically caused by ______.

ultraviolet light

Rank the following mutations from most likely to undergo reversion (at the top) to least likely.

1. transition 2. insertion of 2 base pairs 3. deletion of 5 base pairs

What is our current estimate of the rate of spontaneous mutations in eukaryotic organisms?

About 10-6 mutations per gene per gamete

Hydroxylamine

Adds -OH to cytosine, allowing it to pair with adenine.

Ethylmethane sulfonate

Adds an ethyl group to guanine, which then pair incorrectly

Ethylmethane sulfonate

Alkylating agent

Which of the following represents a reverse mutation of an allele to a wild-type allele that is recessive to the mutant allele?

A— → a+

5-Bromouracil

Base analog

How does proflavin cause mutations?

By intercalating between base pairs

Hydroxylamine

Hydroxylating agent

Which of the following accurately describes a mechanism by which spontaneous heritable mutations can appear?

In order for a heritable mutation to appear, DNA must be altered and replicated before it is repaired.

Which of the following accurately describes the trinucleotide repeat mutations that lead to fragile X syndrome?

More than 200 CGG repeats are found in the 5' UTR of the FMR-1 gene.

Which of the following statements accurately compares the mutation rates of bacteria with those of multicellular eukaryotes?

Multicellular eukaryotes have higher mutation rates because many chances exist for mutations to accumulate in germ-line cells.

Which of the following statements accurately describes the relationship between a mutant allele and the wild-type allele from which it originated?

Mutant alleles can be either recessive or dominant to the original wild-type allele.

A set of independent bacterial cultures were grown, then exposed to phage and plated in media that allowed only phage-resistant bacteria to form colonies. Results were as shown. What conclusion can you draw from these results?

Mutations arose spontaneously before exposure to the phage.

What best explains why multicellular organisms have a higher mutation rate than bacteria?

Mutations may occur at multiple stages of development before gametes form.

The notation A+→ a- represents ______.

a forward mutation where the mutant allele is recessive to the wild-type allele

Alkylating agents cause mutations by _____.

adding methyl or ethyl groups that disrupt base pairing

Hydroxylating agents mutate DNA by ______ a(n) ______ group to(from) cytosine, which allows it to pair with adenine.

adding; -OH

Nitrous acid removes a(n) __________ group from adenine or cytosine, changing the bases to which they can pair. This leads to mutations in the newly-synthesized DNA strand during DNA replication.

amine

Certain compounds have a structure similar to normal DNA bases and so can be incorporated into daughter strands during DNA replication. These compounds are called base

analogs

Consider the following change in a DNA sequence (for simplicity only one of the DNA strands is written): 5'-AATGTGGATG-3' to 5'-AATGTGCATG-3'. What type of mutation is this?

base submition

In humans, the normal HD+ allele has _____.

between 6 and 28 CAG repeats

Mutagens are sometimes called __________ because mutations cause cancer.

carcinogens

The Ames test assays whether a chemical agent ____.

causes mutations

One type of DNA damage converts a cytosine to a uracil, which changes a C-G base pair to a T-A base pair after replication. This damage is due to loss of an amino group, or _____.

deamination

A mutation that removes an adenine or guanine from the DNA is known as a ______.

depurination

Ultraviolet light causes the formation of thymine ___________ in DNA.

dimers

Pre-mutation alleles causing fragile X syndrome ______.

do not expand appreciably in sperm

A mutation that changes a wild-type allele of a gene to a different allele is called _________ mutation.

forward

In humans, the mutant HD allele is considered a _____.

gain-of-function mutant allele

Because they prevent protein production, non-polyQ disease alleles such as those causing fragile X syndrome, are considered ____.

loss-of-function alleles

Alkylating agents covalently attach __________ or ____________ groups to DNA bases, and thus disrupt their normal base pairing properties.

methyl, ethyl

Deaminating agents like nitrous acid cause mutations by _____.

modifying bases and thus altering their normal base-pairing properties

An agent that can change DNA structure and cause mutations is known as a(n) _________.

mutagen

Spontaneous mutations _____.

occur at a very low rate

In most organisms (for example, bacteria or humans), the rate of spontaneous mutations introduced during DNA replication is less than ____.

once in 10^9 base pairs

The average mutation rate of humans is about 1 mutation per _____.

one hundred million base pairs

In his experiments with Drosophila, Muller exposed male flies to increasingly large doses of X-rays and mated them to females that had a Bar-marked Balancer X chromosome. Bar-eyed F1 females carrying a paternal X chromosome with a lethal mutation would _______.

produce sons only with Bar eyes

In order to simulate the effect of mammalian metabolism on the tested agent, scientists performing the Ames test add enzymes isolated from _______ ________.

rat liver

A chemical agent is being assayed for mutagenicity using the Ames test. This agent would be judged to be a mutagen if the number of bacterial colonies on the test plate is ______.

significantly higher than that of the control plate

Trinucleotide repeats can expand or contract due to _____.

slipped mispairing during DNA replication

A change of one DNA base to one of the other three DNA bases is described as a base ______ mutation.

substitution

A temporary change in the structure of a nitrogen base due to movement of hydrogen atoms is called a(n)

tautomerization

A tautomerization is a ____.

temporary change in base structure

Nitrous acid removes a(n) _________ group from adenine or cytosine, changing the bases to which they can pair. This leads to mutations in the newly-synthesized DNA strand during DNA replication.

NH2

Why are the forward mutation rate and the reverse mutation rate not identical for any given gene?

Only one or a few nucleotides within a gene can be mutated to revert a mutant allele so that it functions like a wild-type allele.

Based on current estimates, each human child's genome contains, on average, about _____.

60 base-pair differences compared to their parents' genomes.

Which of the following base changes is a transition mutation?

A to G

In polyQ trinucleotide repeat expansion disorders, the repeat sequence is _____.

CAG

Choose all symptoms of Huntington disease.

Cognitive decline Muscle coordination difficulties

A mouse has a mutation in the DNA polymerase gene that impairs its 3'-to-5' exonuclease domain. What consequence would you expect?

DNA replication will have a higher error rate.

Nitrous acid

Deaminates cytosine and adenine, changing their pairing properties

Nitrous acid

Deaminating agent

The removal of an amino group from a base is called _______.

Deamination

What would be the expected characteristics of a mutagen that acts as an intercalating agent?

Flat, planar molecule

Which types of mutations change the number of nucleotides in a gene? (Choose all that apply.)

Insertions Deletions

Proflavin

Intercalates into the double helix, causing deletions and insertions

Proflavin

Intercalating agent

5-Bromouracil

Is incorporated into DNA instead of thymine, but can pair with guanine

Which of the following statement about fragile X syndrome is true?

It affects males twice as often as females.

When a mutant allele specifies a protein with functions qualitatively different from those of the corresponding wild-type protein, it is called a ______.

gain-of-function allele

Proteins associated with polyQ trinucleotide repeat expansion disorders contain long tracts of the amino acid

glutamine

Base analogs induce mutations by ______.

incorporation into DNA instead of normal bases and tautomerization.

Pre-mutation alleles of genes implicated in trinucleotide repeat diseases ______.

tend to expand in either the female or male germ lines, but not both.

Unstable trinucleotide repeats are repeated sequences of three bases ____.

that can increase or decrease in number generation after generation.

an __________ is a type of base substitution that involves a change of a pyrimidine to another pyrimidine, or a purine to another

transition

The Ames test uses a strain of the bacterium Salmonella typhimurium that is _____.

unable to produce histidine