Q&A Hero

Biology & Life Science

Q: What are the approximate positions of consensus sequences (modular elements) at the 5"² end of eukaryotic genes?
Q: Name three consensus sequences or modular DNA sequences that exist upstream from the coding regions of some eukaryotic genes.
Q: Describe the difference between a focused promoter and a dispersed promoter.
Q: Describe three characteristics of enhancers and silencers.
Q: Enhancers are said to be cis-acting. What is meant by cis-acting, and what are enhancers?
Q: Describe the general structure of a transcription factor.
Q: In what way is 5"²-azacytidine used (experimentally) in the treatment of sickle-cell anemia?
Q: In what way can 5"²-azacytidine influence transcription?
Q: Describe how nucleosomes may influence gene transcription.
Q: Transcription factors appear to be important molecules relating to the regulation of gene activity. Two general classes of transcription factors exist in eukaryotes. Briefly describe each.
Q: List at least three levels or types of genetic regulation in eukaryotes.
Q: Because of the imprecision of molecular joining, recombination between LV and J regions shows considerable variation. Which additional circumstance contributes to this variation? A) transmutation B) hypermutation C) transfection D) conjugation E) transduction
Q: The two major components of the immune system are humoral and cellular immunity. The humoral component ________. A) is involved in the production of antibodies B) allows the T cells to produce antigens that then stimulate antibody production C) plays a major role in the production of antigens D) suppresses the production of T cells E) is responsible for allowing horizontal gene transfer
Q: UASs (upstream activating sequences) are DNase hypersensitive. This means that ________. A) a UAS is constitutively open B) more than one strand of DNA exists in each UAS C) each UAS is likely to be single-stranded D) each UAS has more histone-binding sites than non-UAS sites E) any given UAS is composed of a double-stranded site with a bound repressor
Q: What is the general position of the consensus sequence called the GC box? What is its sequence? A) promoter; CAAT B) promoter; GGGCGG C) terminator; CAAT D) terminator; GGGCGG E) attenuator; GGGCGG
Q: Channels between chromosomes in the interphase nucleus are called ________. A) extrachromosomal elements B) localized zones C) nonlocalized zones D) interchromosomal compartments E) subchromosomal territories
Q: Considering the location of genes in the interphase nucleus, certain chromosomal territories appear to exist. Specifically, ________. A) each chromosome appears to occupy a discrete domain B) gene-poor regions of chromosomes are located outside the nucleus, whereas gene-rich C) regions are located inside the nucleus D) even-numbered chromosomes are located in the interior of the nucleus, whereas odd-numbered chromosomes are located peripherally E) large chromosomes are more likely to be located in the center of the nucleus F) small chromosomes are more likely to be located in the center of the nucleus
Q: DNA methylation may be a significant mode of genetic regulation in eukaryotes. Methylation refers to ________. A) altering RNA polymerase activity by DNA modifications B) changes in DNA-DNA hydrogen binding C) altering translational activity especially of highly methylated tRNAs D) alteration of DNA polymerase activity by addition of methyl groups to glycine E) residues F) addition of methyl groups to the cytosine of CG doublets
Q: Which process seems to be the most similar between eukaryotic and prokaryotic genetic regulation?A) transcriptional regulationB) RNA splicing regulationC) intron/exon shufflingD) 5-²-capping regulationE) poly(A) tail addition
Q: In what way do upstream activator sequences (UASs), regulatory sequences in yeast, differ from enhancers and silencers?A) UASs function only downstream.B) UASs function only upstream.C) Enhancers function only downstream.D) UASs function in the middle of transcription units.E) UASs can function only in the 5-²-3-² direction.
Q: Two modular elements that appear as consensus sequences upstream from RNA polymerase II transcription start sites are ________. A) microsatellites and transposons B) rDNA and nucleolar organizers C) TATA and CAAT D) TTAA and CCTT E) enhancers and telomeres
Q: Which of the following clusters of terms applies when addressing enhancers or silencers as elements associated with eukaryotic genetic regulation? A) cis-acting, variable orientation, variable position B) trans-acting, fixed position, fixed orientation C) cis-acting, fixed position, fixed orientation D) cis-acting, variable position, fixed orientation E) trans- and cis-acting, variable position
Q: Regarding the trp operon, trpR maps to a considerable distance from the structural genes. The mutation either inhibits the interaction with tryptophan or inhibits repressor formation entirely. In the presence of tryptophan in the medium, would you expect the trp operon to be transcriptionally active? Explain.
Q: The catabolite repression system in E. coli essentially represses the lac operon when glucose is present. What evolutionary advantage would favor evolution of such a system?
Q: Describe the positive control exerted by the catabolite activating protein (CAP). Include a description of catabolite repression.
Q: The cAMP-CAP complex and RNA polymerase bind more efficiently to the lac operon together than either does alone. What term is applied to this increased efficiency of binding?
Q: What symbols are used to describe constitutive mutations at specific regions of the lac regulatory system?
Q: What experimental results would indicate that the mutation lacIs is dominant to lacI+?
Q: Explain why lacOc mutations are cis-acting while lacI mutations can be trans-acting.
Q: What is the function of the lacY gene in the lac operon?
Q: A constitutive mutation in the lac operon may be of several types. Name two types of constitutive mutations.
Q: Describe what is meant by a gratuitous inducer. Give an example.
Q: The accompanying table lists several genotypes associated with the lac operon in E. coli. For each, indicate with a "+" or a "" whether β-galactosidase would be expected to be produced at induced levels.
Q: The table below lists several genotypes associated with the lac operon in E. coli. For each, indicate with a "+" or a "" whether functional β-galactosidase would be expected to be produced at induced levels.
Q: (a) Describe by labeled diagram the structural components of thelac operon in E. coli. (b) State the function of the lac regulator gene. (c) State the function of β-galactosidase in the lac system. (d) Show by diagram the manner in which lactose brings about transcription of the three structural genes of the lac operon. (e) Explain why certain mutations in the regulator gene (I) of the lac system result in maximal synthesis of β-galactosidase, permease, and transacetylase even in the absence of the inducer (lactose).
Q: Present a detailed description of the actions of the regulatory proteins in inducible and repressible enzyme systems.
Q: Certain mutations in the regulator gene of the lac system in E. coli result in maximal synthesis of the lac proteins (β-galactosidase, etc.) even in the absence of the inducer (lactose). Provide an explanation for this observation.
Q: In the accompanying diagram, what type of control, positive or negative, is operating?
Q: Present an overview of prokaryotic regulation in terms of growth efficiency.
Q: Compare and contrast positive and negative control of gene expression in bacteria.
Q: The ara operon is controlled by a regulator protein that exerts ________. A) induction and expression B) expressivity and penetrance C) positive and negative control D) upward and reverse control E) top and bottom control
Q: What two important domains within a riboswitch involve the ligand-binding site? A) aptamer and expression platform B) A site and B site C) B site and C site D) alpha and beta E) conformation and anticonformation
Q: Genetic regulation in prokaryotes can involve alterations in RNA secondary structure. What phenomenon occurs in the trp operon that involves such alterations? A) transcription B) capping C) polyadenylation of the 3"² end of the mRNAs D) intron processing E) attenuation
Q: 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, ________. A) the trp 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
Q: Which of the following terms best characterizes catabolite repression associated with the lac operon in E. coli? A) inducible system B) repressible system C) negative control D) positive control E) constitutive
Q: In the lac 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 -linkage of lactose E) forming ATP from pyruvate
Q: Which term most appropriately refers to a regulatory protein in prokaryotes? A) translation B) RNA processing C) DNA binding protein D) gyrase action E) helicase activation
Q: What term refers to a contiguous genetic complex that is under coordinated control? A) lysogen B) prototroph C) operon D) allosteric E) attenuation
Q: What term would be applied to a regulatory condition that occurs when protein is associated with a particular section of DNA and greatly reduces transcription? A) negative control B) positive control C) induction D) activation E) stimulation
Q: The trp and lac operons are both subject to forms of control that are typically called negative.
Q: Attenuation involves the termination of mRNA synthesis.
Q: Attenuation is known to occur in the lac operon.
Q: The trp operon is typically characterized as being both under negative control and repressible.
Q: The enzyme permease cleaves the linkage between glucose and galactose residues in lactose.
Q: Regarding the lactose utilization system in E. coli, a gratuitous inducer is a molecule that is chemically analogous to lactose and induces the operon, but is not a substrate for the enzymes of the lac operon.
Q: Regarding the lactose utilization system in E. coli, a constitutive mutant is one in which the three enzymes are produced regardless of the presence or absence of lactose.
Q: The lac operon consists of three structural genes as well as the adjacent region of DNA known as the regulator.
Q: Under a system of negative control, genetic expression occurs unless such expression is shut off by some form of regulator.
Q: Under a system of positive control, transcription does not occur unless a regulator molecule directly stimulates RNA production.
Q: Monod discovered that if tryptophan is present in relatively high quantities in the growth medium, the enzymes necessary for its synthesis are repressed. How does this occur?
Q: State whether the following statement is true or false, then give your reasoning. The terminating "hairpin" loop occurs in the trp operon when sufficient tryptophan is present.
Q: What is an allosteric molecule?
Q: Regarding regulation of the trp operon, what might one appropriately call the amino acid tryptophan?
Q: Within the control region of the trp operon is a section of DNA that is sensitive to levels of tryptophan in the system. What is the name of this region?
Q: IS (insertion sequences) elements are stable DNA occupants of prokaryotic genomes that are not found among eukaryotes.
Q: Postreplication repair is a system that responds after damaged DNA has escaped repair and failed to be completely replicated.
Q: Strand discrimination during the process of DNA repair is based on DNA methylation in E. coli.
Q: A missense mutation causes premature chain (protein) termination.
Q: Pyrimidine dimers are typically caused by the mutagen 2-aminopurine.
Q: A 2-aminopurine is an alkylating agent.
Q: The shorter the wavelength of a radiation source, the greater its likelihood of causing damage.
Q: When treating an organism with a mutagen, although it is possible that homozygous mutations will occur, it is more likely that most new mutations will be heterozygous or hemizygous.
Q: Certain base analogs such as 5-bromouracil cause mutations by chemically altering nitrogenous bases in nonreplicating DNA.
Q: Although mutation is the original source of genetic variation, its influence on changing allelic frequencies is relatively minor.
Q: Of the two cell lines that can contain a mutation in an organism, somatic and germ line, the latter is more consequential to subsequent generations.
Q: Loss-of-function mutations eliminate the function of a gene product and may be dominant or recessive.
Q: What are LINES?
Q: How were insertion sequences (IS elements) first discovered?
Q: Describe the action of the enzyme transposase.
Q: What is the Ames test, and how does it work?
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