Genetics Smartbook 7

Match Mutagen to its category 1. 5-Bromouracil 2. Hydroxylamine 3. Ethylmethane sulfonate 4. Nitrous acid 5. Proflavin

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

What is our current estimate of the 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

How does proflavin cause mutations?

By intercalating between base pairs

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

CAG

Choose all symptoms of Huntington disease.

Cognitive decline Muscle coordination difficulties

Base excision repair relies on enzymes called ___ ___ that cleave altered bases from the sugar of their nucleotide

DNA glocosylases

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.

Match the diseases to the failed DNA repair system ~breast cancer

Double-strand break repair by homologous recombination

Which of the following statements accurately describes nonhomologous end-joining (NHEJ)?

During NHEJ the two broken ends of DNA are directly attached back together.

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.

Why are several forms of cancer associated with defects in DNA repair systems?

Failure of DNA repair allows mutations to accumulate that can lead to unregulated cell division.

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

Flat, planar molecule

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.

Double-strand breaks are typically repaired by which of the following?

Homologous recombination repair Nonhomologous end-joining

Hydroxylamine is added to it. It causes the addition of the OH group to the N from the NH2.

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

If the proofreading ability of DNA polymerase fails and it inserts the wrong base, which of the following is most likely to be able to fix the resulting mutation?

Methyl-directed mismatch repair

Match the diseases to the failed DNA repair system ~Hereditary colorectal cancer

Mismatch repair

Match the diseases to the failed DNA repair system ~Xeroderma pigmentosum

Nucleotide excision repair

What type of error-prone DNA repair involves "sloppy" DNA polymerases that are attracted to stalled replication forks, where they insert random nucleotides?

SOS System

One type of error-prone DNA repair involves "sloppy" DNA polymerases that are attracted to stalled replication forks where they add random nucleotides. This type of DNA repair is known as the

SOS system

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

Replica Plating

The illustration shows cells in a plate. They are transferred to a cloth below. Then, it leads to a plate with several dotted round shapes, almost the size of the cells. It below leads to a cell on a plate

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.

What is necessary for the cell to enzymatically correct a thymine dimer?

What is necessary for the cell to enzymatically correct a thymine dimer?

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

a base substitution

Base excision repair is the main system used in the repair of _____.

abnormal bases

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

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.

amino

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

Replica plating is a technique in which ______.

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

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

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

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

TThe two main mechanisms used to repair DNA double-strand breaks are ___ and __

homologous recombination nonhomologous end-joining

Base analogs induce mutations by ______.

incorporation into DNA instead of normal bases and tautomerization ~because so similar in chemical structure to the normal nitrogenous bases

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

methyl ethyl

During DNA replication, a base that does not obey the normal base pairing rules is added. This type of replication error will most likely be corrected by ______.

methyl-directed mismatch repair

Deaminating agents like nitrous acid cause mutations by _____.

modifying bases and thus altering their normal base-pairing properties

A heritable change in the genetic material is called a

mutation

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 109 base pairs

The enzyme that can recognize thymine dimers and split them is called ____ he enzyme that can remove methyl and ethyl groups from guanine is called ___

photolyase alkyltranferase

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

Base excision repair

removes DNA damage from oxidation, deamination and alkylation, or single strand breaks.

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

tautomerization

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 trinucleotide repeats.