Genetics Exam III

(Comprehension Q) Expression levels of the lac operon in wild-type cells are < 1% in the absence of lactose and 100% in the presence of lactose, respectively. Which of the following correctly estimates the expression level of the lac operon in a lacI-mutant strain in the absence of lactose?

100%

(Comprehension Q) Expression levels of the lac operon in wild-type cells are < 1% in the absence of lactose and 100% in the presence of lactose, respectively. Which of the following correctly estimates the expression level of the lac operon in a lacO-mutant strain in the absence of lactose?

100%

(Comprehension Q) During attenuation, when tryptophan levels are high, the ( ) stem-loop forms and transcription ( ) the trpL gene. Assume that translation is coupled with transcription.

3-4, ends just past

(Comprehension Q) Which of the following does NOT cause a frameshift mutation?

5'-ATTTCGGGTTAA-3' TO 5'-ATTTAA-3'

(Comprehension Q) A bidirectional enhancer has the following sequence: 5'-GTCA-3' 3'-CAGT-5' Which of the following sequences would also be a functional enhancer?

5'-TGAC-3' 3'-ACTG-5'

A mutagen that is a base analog is

5-bromouracil.

Which of the following is NOT due to a position effect?

A change in gene expression due to a down promoter mutation

Which of the following is NOT an example of a spontaneous mutation?

A mutation caused by UV light

Which of the following is NOT an example of an induced mutation?

A mutation caused by an error in DNA replication

Which of the following is an example of a somatic mutation?

A mutation in an adult skin cell

Which of the following is an example of a germline mutation?

A mutation in an egg cell

(Comprehension Q) A point mutation occurs in the middle of the coding sequence for a gene. Which type of mutation, silent, missense, and nonsense, would be most likely to disrupt protein function?

A nonsense mutation would most likely to disrupt protein function, because it would cause the protein to be much shorter.

Which of the following combinations will cause the rate of transcription to decrease?

A repressor plus a corepressor

Which of the following combinations will cause the rate of transcription to increase?

A repressor plus an inducer

(Comprehension Q) The following data were obtained from a reporter assay experiment using skin cells and liver cells. Identify enhancer and silencer regions. See textbook p391-392 (Problem Sets & Insights) Region deleted % Beta-Gal activity % Beta-Gal activity (Skin) (Liver) None 100 100 A 100 220 B 180 100 C 100 35 D 23 100 E 100 100 F (core promoter) <1 <1

A: Silencer (Liver), B: Silencer (Skin), C: Enhancer (Liver), D: Enhancer (Skin)

What is an operon?

All of these are true for an operon.

Which of the following combinations will cause the rate of transcription to decease?

An activator plus an inhibitor

(Comprehension Q) A gene mutation changes a base pair from A:T to G:C. This change causes a gene to encode a truncated protein that is nonfunctional. A bacterial cell carries this mutation cannot survive at high temperatures. Pick a correct list of the genetic terms that best describes this types of mutation.

At the DNA level: A transition Its effect on the amino acid sequence: A nonsense mutation Its effect on phenotype: A conditional mutation

A gene mutation changes a base pair from A:T to C:G. This change causes a glycine to proline change in the coding sequence, which renders the encoded protein less functional. An organism that carries this mutation at the homozygous state dies during the developmental stage. Pick a correct list of the genetic terms that best describes this type of mutation.

At the DNA level: A transversion Its effect on the amino acid sequence: A missense mutation Its effect on phenotype: A lethal mutation

(Comprehension Q) Depurination creates an apurinic (AP) site. If not repaired, it can cause a base substitution during DNA replication (see Fig. 19.7). Which of the following may repair AP sites prior to DNA replication?

Base excision repair

(Comprehension Q) Methylated cytosine bases tend to produce hotspots for spontaneous mutations. Which of the following mutations is typically observed at a C:G base pair in which the cytosine is methylated?

C:G > T:A

In eukaryotes, gene transcription can be regulated by the binding of activators to enhancers. Which of the following does NOT correctly describe the function of enhancers?

Can work even in a distance (even several kilobases away) due to the formation of a DNA loop via an interaction between TFIID and activator

In eukaryotes, gene transcription can be regulated by the binding of repressors to silencers. Which of the following does NOT correctly describe the function of silencers?

Can work even in a distance (even several kilobases away) due to the formation of a DNA loop via an interaction between TFIID and repressor.

(Comprehension Q) For an Ames test, two different His- strains are available; one detects base substitutions (His-A) and the other frameshift mutations (His-B). After culturing these strains with ethyl methanesulfonate (EMS) separately, we plated cells on media lacking histidine. Which of the following correctly predicts the results from this experiment?

Compared to untreated control groups, the number of revertant colonies should be increased for His-A strain (base substitutions) but not for His-B strain (frameshift mutations).

What is the mechanism by which UV-rays induce mutations?

Creating thymine dimers

(Comprehension Q) The following data were obtained from a reporter assay experiment. Identify enhancer and silencer regions. See textbook p391-392 (Problem Sets & Insights) Region deleted % Beta-Gal activity None 100 A 100 B 220 C 100 D 23 E 100 F (core promoter) <1

D: Enhancer, B: Silencer

Which of the following enzymes recognizes abnormal base structures during base excision repair?

DNA N-glycosylases

Which of the following enzyme is involved in the step that synthesizes a new DNA strand in base excision repair in bacteria?

DNA polymerase I

Which of the following enzymes works together with flap endonuclease in the step that synthesizes normal DNA during base excision repair in eukaryotes?

DNA polymerase delta

(Comprehension Q) Which of the following events is NOT involved in transcription of eukaryotic genes? (See Fig. 15.13)

Histone deacetylation ahead of RNA polymerase

Which of the following statements is incorrect about nonhomologous end joining (NHEJ)?

It is a highly accurate process, because two broken DNA ends are simply pieced back together.

How can methylation at a CpG island affect transcription?

It may promote the binding of methyl-CpG binding proteins, which coverts the chromatin to a closed conformation to inhibit transcription.

Which of the following statements is correct about homologous recombination repair (HRR)?

It primarily uses a sister chromatid as a template to repair a DNA double strand break in the other sister chromatid during the S and G2 phases of the cell cycle.

In DNA repair by nucleotide excision repair, which of the following is NOT one of the steps that occurs?

Joining two broken double strand DNA ends

Which of the following is NOT involved in transcriptional activation?

Methylaion of DNA

Which of the following enzymes recognizes base mismatches during mismatch repair?

MutS

(Comprehension Q) Marfan syndrome is a genetic disease of the connective tissue. It is caused by an autosomal dominant mutation within a gene called FBN1. Among 1,000,000 live births, 200 babies developed this disease. Among those 200 babies, 180 of them had one parent with Marfan syndrome. Calculate mutation rate and mutation frequency at this gene.

Mutation rate: 1 x 10-5, Mutation frequency: 1 x 10-4

Which of the following statements is false?

Mutations occur very frequently.

DNA double-strand breaks are repaired by

NHEJ and HRR

(Comprehension Q) The combination of a 3-4 loop and a U-rich attenuator sequence in the trp operon (see Fig. 14.12) is an example of a rho-independent terminator (intrinsic terminator). Would you expect attenuation to occur if the tryptophan levels were high and mutations changed the attenuator sequence from UUUUUUUU to UGGUUGUC?

No, attenuation would not occur, because the presence of G/C in this sequence increases hydrogen bonds so that the dissociation of mRNA from its template DNA is less likely to occur to terminate transcription.

Steroid hormones act as effector molecules for transcription activators. Which of the following is NOT involved in the mechanism by which steroid hormones regulate gene expression?

Phosphorylation of steroid receptors

When an activator interacts with mediator, what is the result?

RNA polymerase can switch to the elongation stage of elongation.

Regulatory transcription factors (activators/repressors) interact with

TFIID and mediator

Which of the following enzymes recognizes thymine dimers during nucleotide excision repair?

The UvrA/UvrB complex

Which of the following does NOT happen for the CREB protein to activate gene expression?

The binding of a small effector molecule to bind to the CREB protein.

Which of the following does NOT happen for the CREB protein to activate gene expression?

The binding of a small effector molecule to the CREB protein.

Which of the following characteristics is typical of a eukaryotic gene that can be transcribed?

The core promoter is found in a nucleosome-free region.

With regard to lac operon regulation via catabolite activation protein (CAP), which of the following statements is correct in the absence of glucose?

The level of cAMP is high enough to bind to CAP, so CAP is able to bind to the CAP site to increase transcription.

Operons involved in with the biosynthesis of molecules such as amino acids (e.g., tryptophan) are most likely to be regulated in which of the following way?

The product of the biosynthesis pathway represses transcription.

Operons involved with the biosynthesis of molecules such as amino acids (e.g., tryptophan) are most likely to be regulated in which of the following way?

The product of the biosynthesis pathway represses transcription.

Operons involved with the catabolism (breakdown) of substances such as sugars (e.g., lactose) are most likely to be regulated in which of the following way?

The substance to be broken down or related compound often act as the inducer to increase transcription.

(Comprehension Q) In E. coli, a methyltransferase enzyme encoded by the dam gene recognizes the sequence of 5'-GATC-3' and attaches a methyl group to the nitrogen at position 6 of adenine. E. coli strains that are missing the dam gene are known to have higher rates of spontaneous mutations than wild-type strains. Why?

This is because these strains are unable to recognize the parental strand as a repair template to remove incorrect bases in the daughter strand during mismatch repair.

Which of the following is NOT an example of a point mutation?

a frameshift mutation

Binding of ( ) to ( ) decreases the rate of transcription.

a repressor, a silencer

In the ( ) of glucose, the binding of ( ) to CAP occurs, which causes CAP to ( ) to the CAP site, thereby ( ) transcription.

absence, cAMP, bind, increasing

The function of alkyltransferase is to repair

alkylated guanines

EMS (ethyl methanesulfonate ) causes base substitutions by ( ) bases.

alkylating

What of the following is an advantage of gene regulation?

all of these

Regulatory transcription factors can be modulated by

all of these.

The binding of ( ) to lac repressor causes lac repressor to ( ) to the operator site, thereby ( ) transcription.

allolactose, not bind, increasing

The binding of ( ) to the lac repressor disables the lac repressor to bind to the ( ) site, thereby ( ) transcription.

allolactose, operator, increasing

Binding of ( ) to ( ) increases the rate of transcription.

an activator, an enhancer

Which of the following is NOT an example of post-translational regulation?

antisense RNA

Eukaryotic genes that can be activated usually have a nucleosome free region

at both the beginning and end of the gene.

Abnormal base structures such as uracil and 3-methyladenine are primarily repaired by

base excision repair

When tryptophan binds to trp repressor, this causes trp repressor to ( ) to the trp operator and ( ) transcription.

bind, inhibit

After DNA replication, mismatch repair systems recognize incorrect bases in the ( ) strand, which is ( ).

daughter, nonmethylated

Nitrous acid replaces amino acid groups with keto groups via a process called

deamination.

A chromatin-remodeling complex may

do all of these.

A mutation that adds one base pair to the coding sequence of a gene would cause a

frameshift mutation.

A mutation that removes two base pair from the coding sequence of a gene would cause a

frameshift mutation.

Proflavin ( ) , creating frameshift mutations.

intercalates within DNA helix

Another way for methylation at a CpG island to affect transcription is that

it may prevent the binding of an activator to an enhancer, thereby decreasing transcription.

The lac operon is regulated by

lac represspr and CAP.

A down promoter mutation causes the promoter of a gene to be ( ) like the consensus sequence and ( ) transcription.

less, inhibits

A mutation that changes a codon that specifies glycine into a codon that specifies glutamic acid is a

missence mutation.

An up promoter mutation causes the promoter of a gene to be ( ) like the consensus sequence and ( ) transcription.

more, stimulates

A mutation is called ( ) mutation, when a change in a single amino acid does not have a noticeable effect on the polypeptide.

neutral

A mutation is called a ( ) mutation, when a change in a single amino acid does not have a noticeable effect on the polypeptide.

neutral

A mutation changes a codon that specifies tyrosine into a stop codon. This type of mutation is a

nonsense mutation.

Human individuals with xeroderma pigmentosum (XP) carry germline mutations in one of the ( ) genes. XP patients are at a high risk of developing ( ), because their cells are unable to repair ( )

nucleotide exicison repair, skin cancer, thymin dimers

An advantage of translesion-replicating polymerases is that they can replicate ( ), but a disadvantage is that they ( ).

over damaged DNA, have low fidelity

The primary function of mediator is to control whether or not RNA polymerase is able to

proceed to the elongation stage of transcription.

A repressor is a ( ) that ( ) transcription.

regulatory protein, inhibits

An activator is a ( ) that ( ) transcription.

regulatory protien, enhances

A ( ) mutation changes a mutant allele back to a wild-type allele.

reverse

In an Ames test, a ( ) number of colonies is observed if a substance ( ) a mutagen, compared with the number of colonies for a control sample that is not exposed to the suspected mutagen.

significantly higher, is

A mutation that changes the base sequence without a subsequent change in the amino acid is a

silent mutation.

Combinatorial control refers to the phenomenon that

the combination of many factors determines the expression of any given gene.

In bacteria, the regulation of gene expression most commonly occurs at

the transcriptional level.

The function of photolyase is to repair

thymine dimers

The rate of translation can be regulated by

translational repressors and antisense RNA.

The trp operon is regulated by

trp repressor and attenunation.

During diauxic growth involving glucose and lactose, bacterial cells

use up glucose first, then they use lactose.