Exam 4 Principles of Genetics

The spontaneous mutation rate cannot be measured in complex animals such as mammals

Which of the following statements about spontaneous mutation rates is FALSE?

Yes, in a transversion mutation

Is it possible to have a mutation, but keep the same number of bases and the same base composition?

Conditional mutation

A mutation arose in the guinea pig genome through the course of evolution that affects the ability to produce ascorbic acid, or vitamin C. The mutation maps to a gene encoding an enzyme in the biosynthetic pathway that produces ascorbic acid. Which term describes this mutation?

Move from place to place within the genome

Transposable sequences are identified by their ability to _____.

Base deletion

Which of the following events could result in a frameshift mutation?

SOS repair

Which repair system uses induces its own DNA mutation?

All of the above

Which of the following is a potential effect of transposons in the genome?

Somatic

Of the following types of mutations, which will not be passed to offspring?

Transition mutations

A tautomeric shift may result in _____.

It does not occur in humans

Which of the following statements about photoreactivation repair is true?

The deletion of a single codon in the gene

While there are several mutations that give rise to cystic fibrosis, a common one results in a missing amino acid at position 508 of the CFTR protein. This is the result of _____.

A spontaneous, somatic mutation

A regulatory mutation has been observed in several individuals in a population. This mutation is NOT transmitted to offspring, so this mutation is most probably _____.

Photoreactivation repair

Which of the following DNA repair mechanisms is most often used by bacteria to repair thymine dimers?

More than one amino acid, or even entire proteins, is affected

Why are frameshifts one of the most severe types of mutations?

Acridine dye

Which of the following can result in frameshift mutations?

NER detects distortions in the double helix, while BER removes damaged bases

A difference between nucleotide excision repair (NER) and base excision repair (BER) is that _____.

That any exposure to X-rays will cause mutations

This graph shows the effect of X-ray dose on number of mutations induced. What can you conclude from it?

The genetic code is degenerate

Base substitutions in a gene exon might NOT result in a change in the gene product because _____.

A transition mutation in the codon UGG could result in a single base substitution to give the new codon CGG

Which of the following statements about a transition mutation in the codon UGG is true?

Formation of pyrimidine dimers

Ultraviolet radiation causes _____.

Transversion

If the normal DNA sequence is AAAAA and the mutant is AATAA, this mutation would be called a:

More than one amino acid, or even entire proteins, is affected

Why are frameshifts one of the most severe types of mutations?

Morphological mutation

Based on our lecture about mutations classified by the phenotype, how would you categorize a mutation in a plant species that caused a reduction in height due to greatly reduced activity in the growth hormone?

The spontaneous mutation rate cannot be measured in complex animals such as mammals

Which of the following statements about spontaneous mutation rates is FALSE?

A shift in the atoms (proton shift) arrangement in the bases, result in base pair changes during DNA replication

Which of the following is correct with respect to tautomeric shifts?

Acridine dye

Which of the following can result in frameshift mutations?

Thymine dimers

A photoreactivation repair system is thought to operate in both prokaryotes and eukaryotes to correct what type of problem in DNA?

All organismic groups

Transposons, or jumping genes, are DNA elements that move within the genome. In which organismic groups are transposons found?

5-Bromouracil and 2-amino purine

Which of the following two mutagens that would be classified as base analogs?

Different genes in the same species have different mtation frequencies

In lecture we discussed mutation frequencies both within and among species. Which of the following is correct with respect to that discussion?

Morphological mutation

Based on our “bunny trail” lecture, how would you categorize a mutation in a plant species that caused a reduction in height due to greatly reduced activity in the growth hormone?

Are usually found in every cell of the next generation

Germ cell mutations _____.

Can cause missense mutations due to mispairings

Tautomeric shifts _____.

A CAP-cAMP complex is required for transcription, and its level is low when glucose is present

When a bacterial cell is present in an environment in which both lactose and glucose are present, the glucose will be metabolized first and the lactose will be used when the stores of glucose have been depleted. How does a bacterial cell recognize the fact that glucose is present and turn off transcription of the lac genes even when lactose is present?

Tryptophan acts as a corepressor, and tryptophan tRNA acts as a signal in attenuation

Which of the following statements explains how the presence of high levels of tryptophan inhibits the expression of genes from the trp operon?

Lactose

Which molecule is the inducer of the lactose operon?

The inducer binds to the repressor

In an inducible operon, induction occurs when _____.

False

The trp repressor binds to the operator when tryptophan is absent, whereas the lac repressor binds to the operator when allolactose is present.

Tryptophan acts as a corepressor, and tryptophan tRNA acts as a signal in attenuation

Which of the following statements explains how the presence of high levels of tryptophan inhibits the expression of genes from the trp operon?

Repression of the trp operon

The direct result of accumulation of tryptophan in bacterial cells is _____.

Region 2

In the following diagram f an operon, “P” is the promoter, “A” is the first gene, and Z the last in the operon. Which region most likely is the operator region?

Results from the formation of secondary structures in the trp mRNA

Attenuation in the E. coli trp operon _____.

The mutant strain cannot use lactose as an energy source

What would be the effect of mutations in a strain of wild-type bacteria that cause it to be lacZ and lacY non-functional?

trpR

The regulatory gene in the trp operon is _____.

Are expressed continuously

Constitutive genes _____.

False

A mutation in the l gene directly affects the promoter of the lac operon.

The presence of lacZ, lacY, and lacA genes on the same RNA

Which of the following is a good example of polycistronic RNA?

Antitermination

During transcription of the trp operon, pairing of regions 2 and 3 in the leader peptide mRNA creates the _____ signal.

In the presence of lactose and the absence of glucose

The lac operon is optimally expressed _____.

Constitutive expression of lac operon, whether or not lactose was present, as the repressor cannot bind

The mutation in the O region of the lac operon would most likely result in _____.

Antitermination

During transcription of the trp operon, pairing of regions 2 and 3 in the leader peptide mRNA creates the _____ signal.

When glucose is present, the levels of cAMP are low. CAP alone will not bind to the CAP binding site, so transcription of the structural genes is diminished

Which of the following statements describes what occurs in a bacterial cell as a consequence of high glucose concentrations?

The lac Z, Y, and A genes would not be expressed

What would be the effect of a mutation in the lacl gene that prevented the repressor from binding to lactose?

The inducer binds to the repressor

In an inducible operon, induction occurs when _____.

It undergoes a conformational change in its active site when it interacts with another molecule

In the lac and trp operons, the repressor is said to be an allosteric molecule because _____.

False

The trp repressor binds to the operator when tryptophan is absent, whereas the lac repressor binds to the operator when lactose is present.

Negative and repressible

Transcription of teh trp operon is under _____ control.

the structural genes of the operon would never be transcribed.

Although rare in nature, mutations occur frequently on genetic exams. One such mutation occurred in the repressor protein gene of the lac operon. The repressor protein from this mutated gene did not have a lactose binding site. Which of the following would be correct for this mutated bacterium?

transcriptional termination is likely

When referring to attenuation in regulation of the trp operon, it would be safe to say that when there are high levels of tryptophan available to the organism, ________.

constantly transcribe the structural genes of the operon.

In a certain strain of bacteria, a mutation in the operator gene of the trp operon resulted in a nonfunctional operator region. This would cause the bacterial strain to:

operon

What term refers to clusters of bacterial genes that are under the control of a single regulatory region?

inducible and under negative control.

The lac operon is:

repressor; constitutively expressed

lacI codes for a(n) ________, and when lacI is mutated, the lac operon is ________.

a sequence of DNA which codes for the amino acid sequence of a polypeptide.

A structural gene may be defined as:

lacY

If lactose is accumulating outside of E. coli and is unable to enter, then which structural gene of the lac operon is most likely mutated?

the structural genes always being transcribed.

A mutation occurred in the repressor protein gene of the lac operon. The protein produced by this mutant gene is not able of binding to the operator. This would result in:

if the ribosome stalls at the trp codons an antiterminator hairpin will be formed and transcription will proceed.

In E. coli, trp biosynthesis is regulated by a repressor protein system and a secondary system called attenuation. Which of the following is correct with respect to the trp attenuation system?

there is no CAP cAMP complex bound to the promoter which greatly decreases transcriptional efficiency.

Glucose is known to regulate the lac operon via catabolite repression. Which of the following is accurate with respect to the effect of glucose?

positive control

Which of the following terms best characterizes catabolite repression associated with the lac operon in E. coli?

constitutive

Enzymes that are continuously produced are said to have a(n) ________ expression.

there is no CAP cAMP complex bound to the promoter which greatly decreases transcriptional efficiency.

Glucose is known to regulate the lac operon via catabolite repression. Which of the following is accurate with respect to the effect of glucose?

the structural genes always being transcribed.

A mutation occurred in the repressor protein gene of the lac operon. The protein produced by this mutant gene is not able of binding to the operator. This would result in:

a DNA segment that serves a regulatory function in the control of transcription.

An operator is:

repressor

Which binds to the operator of the lac operon?

binds to the operator when lactose is rare.

With regard to the lac operon, the repressor protein normally:

a repressor protein, which then dissociates from the operator.

In the functioning of the lac operon, an inducer substance binds to:

the only control of transcription would be attenuation.

A mutation occurred in a bacterial strain resulting in a nonfunctional trp site in the repressor protein for the trp operon. What effect would this mutation have on this system?

binds to the operator when tryptophan is present.

The repressor protein in the trp operon normally:

CAP binds to cAMP and then to the promoter only in the presence of low glucose.

When both lactose and glucose are available to E. coli, which part of the lac operon regulation assures that glucose will be metabolized first?

the availability of charged tRNA trp will determine whether or not transcription continues or is terminated.

The biosynthesis of tryptophan in bacteria is regulated by a repressor protein system and a secondary attenuation system. Which of the following is correct with respect to the trp attenuation system?

transcriptional termination is likely

When referring to attenuation in regulation of the trp operon, it would be safe to say that when there are high levels of tryptophan available to the organism, ________.