Quiz 10 Flashcards

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The tryptophan operon is typically characterized by the following two terms: negative control and repressible.

A. True

B. False



This question relates to regulation of enzymes involved in the synthesis of tryptophan in E. coli. If tryptophan is present in the medium and available to the bacterium

A. the repressor is inactive and the tryptophan operon is "off."

B. the repressor is inactive and the tryptophan operon is "on."

C. the repressor is bound to the operator, thus blocking transcription.

D.the five structural genes associated with tryptophan synthesis are being transcribed at "induced" levels.

E. positive control is occurring.



Which of the following two terms relates most closely to split genes?

A. 5'-cap, 3'-poly-A tail

B. introns, exons

C. elongation, termination

D. transcription, translation

E. heteroduplex, homoduplex



Transcription of the structural genes in an inducible operon

A. occurs continuously in the cell.

B. starts when the pathway's substrate is present.

C. starts when the pathway's product is present.

D. stops when the pathway's product is present.

E. does not result in the production of enzymes.



Most repressor proteins are allosteric. Which of the following binds with the repressor to alter its conformation?

A. inducer

B. promoter

C. RNA polymerase

D. transcription factor




The genetic code is fairly consistent among all organisms. The term often used to describe such consistency in the code is

A. universal.

B. exceptional.

C. trans-specific.

D. overlapping.

E. none of these



A 3' poly-A tail and 5'-cap are common components of prokaryotic RNAs.

A. True

B. False



Genetic regulation in eukaryotes can take place at a variety of levels from transcriptional to posttranslational. At what level is genetic regulation considered most likely in prokaryotes?

A. transcriptional

B. capping

C. polyadenylation of the 3' end of the mRNAs

D. intron processing

E. exon processing



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

A. the tryptophan operon is being transcribed at relatively high levels.

B. translational termination is likely.

C. transcriptional termination is likely.

D. tryptophan is inactivating the repressor protein.

E. ribosomes are stalling during translation of the attenuator region.



An intron is a section of an RNA which gets spliced out.

A. True

B. False



When examining the genetic code it is apparent that

A. there can be more than one amino acid for a particular codon.

B. AUG is a terminating codon.

C. there can be more than one codon for a particular amino acid.

D.the code is ambiguous in that the same codon can code for two or more amino acids.

E. there are 44 stop codons because there are only 20 amino acids.



Under a system of negative control, genetic expression occurs unless such expression is shut off by some form of regulator.

A. True

B. False



What term would be applied to a regulatory condition which occurs when protein greatly reduces transcription when associated with a particular section of DNA?

A. negative control

B. positive control

C. inhibition

D. activation

E. stimulation



Allolactose, an isomer of lactose, is formed in small amounts from lactose. An E. coli cell is presented for the first time with the sugar lactose (containing allolactose) as a potential food source. Which of the following occurs when the lactose enters the cell?

A. The repressor protein attaches to the regulator.

B. Allolactose binds to the repressor protein.

C. Allolactose binds to the regulator gene.

D. The repressor protein and allolactose bind to RNA polymerase.

E. RNA polymerase attaches to the regulator.



What is the term which refers to a contiguous genetic complex which is under coordinate control?

A. lysogen

B. prototroph

C. operon

D. allosteric

E. attenuation



When one speaks of a 5' cap, one is describing the addition of a base, usually thymine, to the 5' end of a completed peptide.

A. True

B. False



If one compares the base sequences of related genes from different species one is likely to find that corresponding ________ are usually conserved but the sequences of ________ are much less well conserved.

A. exons; introns

B. introns; exons

C. introns; chaperons

D. chaperons; exons

E. introns; proteins



A class of mutations which results in multiple contiguous (side-by-side) amino acid changes in proteins is probably caused by the following type of mutation.

A. frameshift

B. transversion

C. transition

D. base analogue

E. recombinant



Transcription factors function to help move ribosomes along the mRNA.

A. True

B. False



Introns are known to contain termination codons (UAA, UGA, or UAG) yet these codons do not interrupt the coding of a particular protein. Why?

A. UAA, UGA, and UAG are initiator codons, not termination codons.

B. Exons are spliced out of mRNA before translation.

C. These triplets cause frameshift mutations, not termination.

D. More than one termination codon is needed to stop translation.

E. Introns are removed from mRNA before translation.



Three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes occur in which cellular organelle?

A. nucleus

B. cytoplasm

C. mitochondrion

D. lysosome

E. Golgi



The triplet AUG is commonly used as a start codon during translation.

A. True

B. False



A mutation that inactivates the regulatory gene of a repressible operon in an E. coli cell would result in

A. continuous transcription of the structural gene controlled by that regulator.

B. complete inhibition of transcription of the structural gene controlled by that regulator.

C. irreversible binding of the repressor to the operator.

D. inactivation of RNA polymerase by alteration of its active site.

E. continuous translation of the mRNA because of alteration of its structure.



Gene expression might be altered at the level of post-transcriptional processing in eukaryotes rather than prokaryotes because of which of the following?

A. Eukaryotic mRNAs get 5' caps and 3' tails.

B. Prokaryotic genes are expressed as mRNA, which is more stable in the cell.

C. Eukaryotic exons may be spliced in alternative patterns.

D. Prokaryotes use ribosomes of different structure and size.

E. Eukaryotic coded polypeptides often require cleaving of signal sequences before localization.



In eukaryotes, general transcription factors

A. are required for the expression of specific protein-encoding genes.

B. bind to other proteins or to a sequence element within the promoter called the TATA box.

C. inhibit RNA polymerase binding to the promoter and begin transcribing.

D. usually lead to a high level of transcription even without additional specific transcription factors.

E. bind to sequences just after the start site of transcription.



What is the initiator triplet in both prokaryotes and eukaryotes? What amino acid is recruited by this triplet?

A. UAA, no amino acid called in

B. UAA or UGA, arginine

C. AUG, arginine

D. AUG, methionine

E. UAA, methionine



Select three posttranscriptional modifications often seen in the maturation of mRNA in eukaryotes.

A. 5'-capping, 3'-poly(A) tail addition, splicing

B. 3'-capping, 5'-poly(A) tail addition, splicing

C. removal of exons, insertion of introns, capping

D. 5-poly(A) tail addition, insertion of introns, capping

E. heteroduplex formation, base modification, capping



Which of the following, when taken up by the cell, binds to the repressor so that the repressor no longer binds to the operator?

A. ubiquitin

B. inducer

C. promoter

D. repressor

E. corepressor



An intron is a section of

A. protein which is clipped out posttranslationally.

B. RNA which is removed during RNA processing.

C. DNA which is removed during DNA processing.

D. transfer RNA which binds to the anticodon.

E. carbohydrate which serves as a signal for RNA transport.



In response to chemical signals, prokaryotes can do which of the following?

A. turn off translation of their mRNA

B. alter the level of production of various enzymes

C. increase the number and responsiveness of their ribosomes

D. inactivate their mRNA molecules

E. alter the sequence of amino acids in certain proteins



In the lactose operon, the product of structural gene lacZ, is capable of

A. nonautonomous replication.

B. forming lactose from two glucose molecules.

C. replacing hexokinase in the early steps of glycolysis.

D. splitting the beta-linkage of lactose.

E. forming ATP from pyruvate.



For a repressible operon to be transcribed, which of the following must occur?

A. A corepressor must be present.

B. RNA polymerase and the active repressor must be present.

C. RNA polymerase must bind to the promoter, and the repressor must be inactive.

D. RNA polymerase cannot be present, and the repressor must be inactive.

E. RNA polymerase must not occupy the promoter, and the repressor must be inactive.



The lactose operon is likely to be transcribed when

A. there is more glucose in the cell than lactose.

B. the cyclic AMP levels are low.

C. there is glucose but no lactose in the cell.

D. the cyclic AMP and lactose levels are both high within the cell.

E. the cAMP level is high and the lactose level is low.



Which of the following is a protein produced by a regulatory gene?

A. operon

B. inducer

C. promoter

D. repressor

E. corepressor



When considering the initiation of transcription one often finds consensus sequences located in the region of the DNA where RNA polymerase(s) bind. Which are common consensus sequences?




D. any trinucleotide repeat

E. satellite DNAs



It has been recently determined that the gene for Duchenne muscular dystrophy (DMD) is over 2000 kb (kilobases) in length, however, the mRNA produced by this gene is only about 14 kb long. What is a likely cause of this discrepancy?

A. The exons have been spliced out during mRNA processing.

B. The DNA represented a double stranded structure, while the RNA is single stranded.

C. There are more amino acids coded for by the DNA than the mRNA.

D. The introns have been spliced out during mRNA processing.

E. When the mRNA is produced, it is highly folded and therefore less long.



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

A. inducible system

B. repressible system

C. negative control

D. positive control

E. constitutive



The role of a metabolite that controls a repressible operon is to

A.bind to the promoter region and decrease the affinity of RNA polymerase for the promoter.

B.bind to the operator region and block the attachment of RNA polymerase to the promoter.

C. increase the production of inactive repressor proteins.

D. bind to the repressor protein and inactivate it.

E. bind to the repressor protein and activate it.



What is the name given to the three bases in a messenger RNA which bind to the anticodon of tRNA to specify an amino acid placement in a protein?

A. protein

B. anti-anticodon

C. cistron

D. rho

E. codon



Under the system of genetic control of the tryptophan operon,

A.when there are high levels of tryptophan in the medium, transcription of the trp operon occurs at high levels.

B.when there is no tryptophan in the medium, transcription of the trp operon occurs at high levels.

C.when there are high levels of tryptophan in the medium, transcription of CAP (CRP) occurs at high levels.

D.when there are high levels of tryptophan in the medium, ribosomes "stall" and reduce the levels of tryptophan synthesized.

E.no transcription occurs under any nutritional circumstance because negative controls inhibit transcription.



There is a mutation in the repressor that results in a molecule known as a super-repressor because it represses the lac operon permanently. Which of these would characterize such a mutant?

A. It cannot bind to the operator.

B. It cannot make a functional repressor.

C. It cannot bind to the inducer.

D. It makes molecules that bind to one another.

E. It makes a repressor that binds CAP.



Regarding the lactose utilization system in E. coli, a gratuitous inducer is a molecule which is chemically analogous to lactose, induces the operon, but is not a substrate for the enzymes of the lac operon.

A. True

B. False



The genetic code is said to be triplet, meaning that

A. there are three amino acids per base in mRNA.

B. there are three bases in mRNA which code for an amino acid.

C. there may be three ways in which an amino acid may terminate a chain.

D. there are three "nonsense" triplets.

E. none of these.



If glucose is available in the environment of E. coli, the cell responds with a very low concentration of cAMP. When the cAMP increases in concentration, it binds to CAP. Which of the following would you expect to be a measurable effect?

A. decreased concentration of the lac enzymes

B. increased concentration of the trp enzymes

C. decreased binding of the RNA polymerase to sugar metabolism-related promoters

D. decreased concentration of alternative sugars in the cell

E. increased concentrations of sugars such as arabinose in the cell



In positive control of several sugar-metabolism-related operons, the catabolite activator protein (CAP) binds to DNA to stimulate transcription. What causes an increase in CAP?

A. increase in glucose and increase in cAMP

B. decrease in glucose and increase in cAMP

C. increase in glucose and decrease in cAMP

D. decrease in glucose and increase in repressor

E. decrease in glucose and decrease in repressor



The lac operon consists of three structural genes as well as the adjacent region of DNA known as the regulator.

A. True

B. False