Chapter 7 Smartbook

Match each mutagen to its category 1. 5-Bromourucail 2. Hydroxylamine 3. Ethylmethane sulfonate 4. Nitrous acid 5. Proflavin

1. Base analog 2. Hydroxylating agent 3. Alkylating agent 4. Deaminating agent 5. Intercalating agent

Match each mutagen to its mechanism of action: 1. 5-Bromourucail 2. Hydroxylamine 3. Ethylmethane sulfonate 4. Nitrous acid 5. Proflavin

1. Is incorporated into DNA instead of thymine, but can pair with guanine 2. Adds -OH to cytosine, allowing it to pair with adenine. 3. Adds an ethyl group to guanine, which then pair incorrectlyAdds an ethyl group to guanine, which then pair incorrectly 4. Deaminates cytosine and adenine, changing their pairing properties 5. Intercalates into the double helix, causing deletions and insertionsIntercalates into the double helix, causing deletions and insertions

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

About 10^-6 mutations per gene per gamete

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 substitution

When changes in DNA appear, they are initially considered "potential" mutations. Why?

Because most of them are repaired before the altered DNA is replicated

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

CAG

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.

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.

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

Flat, planar molecule

A ____ mutation is one that changes a wild-type allele of a gene to a different allele.

Forward

What was the first step in Muller's Drosophila experiment that demonstrated the mutagenic effects of X-rays?

He exposed male flies to X-rays and mated them to females which had a Balancer chromosome carrying a mutation causing Bar eyes.

Based on this diagram, what type of mutagen is 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.

What is one of the main determinants of the mutation rate of a particular gene?

Length of the coding sequence

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.

Any agent that can change DNA structure and cause mutations at a rate above the spontaneous rate is known as a(n) ____.

Mutagen

A heritable change in the genetic material is called a(n) ______.

Mutation

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

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

This figure shows a technique known as ____ ____.

Replica plating

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 daughter molecules

Of two genes, which should be easiest to mutate in a mutant screen?

The longest one

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.

Alkylating agents cause mutations by _____.

adding methyl or ethyl groups that disrupt base pairing

Hydroxylating agents can. introduce mutation in DNA by Blank______ a(n) Blank______ group to(from) cytosine, which allows it to pair with adenine.

adding; -OH

A mutagen is a(n) ______.

agent that causes mutations

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, NH2, or amino

Certain mutagenic 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, analogues, or analog

Replica plating is a technique in which ______.

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

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

base substitution

In humans, the normal HD+ allele has _____.

between 6 and 28 CAG repeats

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

depurination

The removal of a purine from DNA is called ____.

depurination

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

forward mutation

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

glutamine or Gln

Base analogs induce mutations by

incorporation into DNA instead of normal bases, and tautomerization

Deaminating agents like nitrous acid cause mutations by _____.

modifying bases and thus altering their normal base-pairing properties

The term ____ refers to an inherited change in the sequence of the genetic material.

mutation

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

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

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 or tautomer

A tautomerization is a ____.

temporary change in base structure

Unstable trinucleotide repeats are repeated sequences of three bases ____.

that can increase or decrease in number generation after generation

Repeated sequences of three bases that can change in number generation after generation are called unstable ____ repeats.

trinucleotide