Regulation Of Gene Expression In Prokaryotes Homework Market

Unformatted text preview: Question 1 of 30 Which statement describes an operon? protein modifications, such as the addition of a functional group, or alternate folding of the protein the processing of exons in mRNA that results in a single gene coding for multiple proteins mRNA modifications, such as the addition of a 5'-cap and 3' poly-A tail and the removal of introns heritable changes in gene expression that occur without altering the DNA sequence a gene cluster controlled by a single promoter that transcribes to a single mRNA strand Question 2 of 30 An operon is a group of genes under the control of a single promoter. Match each type of operon with the descriptions below. Inducible Repressible Constitutive Transcription stops when the repressor gene product The amount °f gene Transcrigtion is turned on when c molecule is present. is activated. product is constant. a speci Sufficient amounts of the gene product inhibit further transcription. Transcrigtion is turned on when Transcription stops when The amount of gene a speci c molecule is present. the repressor gens product product is constant. is activate . Sufficient amounts of the gene product inhibit further transcription. Question 3 of 30 Match the description of transcriptional control to the corresponding transcriptional regulator. There is one description for each transcriptional regulator. Active repressor Inactive repressor Active activator Inactive activator regulator of a negative negative control in positive control in positive'control in inducible operon a repressible operon an inducible operon a repressuble operon regulator of a negative positive control in positive control in negative control in inducible operon an inducible operon a repressible operon a repressible operon Question 4 of 30 A mutant strain of E. coli produces B—galactosidase in the presence and in the absence of lactose. Where in the operon might the mutation in this strain occur and why? in the promoter region of the operon, where the mutation leads to the failure of the RNA polymerase to bind to the promoter in the operator region, where the mutation leads to the failure of the operator to normally bind the repressor near the lac! gene, where the mutation leads to increased levels of lac repressor being made in the operator region, which leads to increased binding of the lac repressor to the operator in the lacl gene, which leads to an inactive lac repressor in the CAP binding site, where the mutation leads to the inefficiency of RNA polymerase activity [I I I E] E] El Question 5 of 30 The lac operon in E. coli controls the gene expression of the enzymes that digest lactose in the cell. In the absence of lactose, the lac operon will turn off and gene expression will be inactivated. Place the events of gene regulation by the lac operon in order of their occurrence, from the removal of lactose from the environment to when the cell no longer digests lactose. Lactose is scarce in the environment. The repressor is activated in the absence of lactose. The repressor binds to the operator. RNA polymerase is prevented from moving from the promoter. Lactose enzyme genes are not transcribed. The cell no longer digests lactose. The repressor is The repressor binds RNA polymerase is activated in the to the operator. prevented from moving absence of lactose. from the promoter. Lactose enzyme genes are not transcribed. Question 6 of 30 The lac operon contains three genes: lacZ, IacY, and IacA (for B—galactosidase, galactoside permease, and thiogalactoside transacetylase, respectively). The operon also contains a promoter site and an operator site. The regulatory gene includes the Igene for the Lac repressor protein and a promoter for that gene. regulatory gene lac operon (—/%l f A 1 DNA a - P 0 level gene The lac operon undergoes negative regulation. In the normal condition, the Lac repressor protein is active. Allolactose, an isomer of lactose. is the signal molecule that binds to the Lac repressor. Determine which events will increase the concentration of gene products and which will decrease the concentration of lac gene products. Increase in gene products Decrease in gene products _The _Lac repressor Allolactose is dissomates from DNA. not resent Allolactose binds mt e cell. to the Lac The Lac repressor repressor protein. renti‘ains bound Lactose is tot e operator. present in the cell. The l ene is disa led. The l ene Lactose is Allolactose binds The Lac repressor Allolactose is The Lac repressor is disa led. present in to the Lac dissociates from DNA. not resent remains bound the cell. repressor protein. in t e cell. to the operator. Question 7 of 30 Lactose metabolic activity in the lac operon is represented in the image below. D RNA polymerase “A W D $2.2m" “mow-v OFF \ ' \ ’ Enzymfor \ | lactose uliliulion For the lac genotypes listed below, the repressor mutant I" cannot bind to the operator, the IS mutant always binds to the operator, and the OC mutation prevents the repressor from binding the operator. The F' plasmid delivers the wild-type operator, 0*, and I“ gene into the mutant strains. Determine the nature of the expression of the lac genes, L, and label each genotype as constitutive, inducible, or repressed. Assume that all promoters are wild type. r 0* U Q r 0* Lt F' g I‘ 0*“ - ISOT g 1* 0th F' - IS 0* Lt F' g g-g Question 8 of 30 When the level of glucose in the environment is low, abundant cyclic adenosine monophosphate (cAMP) binds the catabolite activator protein (CAP) to form the CAP-CAMP complex, which binds DNA. When CAP— cAMP binds DNA, the efficiency of RNA polymerase binding is increased at the lac operon promoter, which increases transcription of the structural genes. However, when glucose levels are high, the CAP— cAMP complex does not form and RNA polymerase cannot bind to the promoter efficiently. ® , m Low glucose @ g I g ‘9 1%me W \ _—> m High glucose Is the lac operon inducible or repressible? O inducible 0 cannot determine 0 repressible Continued below... What type of protein regulates structural-gene expression as a result of glucose level? . activator O repressor 0 cannot determine Continued below... What type of overall gene regulation occurs as a response to glucose level? . positive 0 negative 0 neither Question 9 of 30 Classify the following examples of prokaryotic gene expression as positive or negative gene regulation. Positive gene regulation Negative gene regulation In the presence of lactose and low Iucose, In the absence of lactose, the lacR the lac operon is expressed 20-fol higher repressor protein binds the lac operon. ' h fl . than In t e absence 0 actose In the presence of iron, the dth repressor - - - - tein binds DNA and the gene that encodes If the sugar arabinose Is present, an activator protein pro . .' . . binds the promoter of the enes responsible for for the dlphthena tox'" '5 "0t expressed. processing arabinose and in uces their transcription. When excess tryptophan is present, a repressor protein binds the operator of the trp operon and prevents the operon from being transcribed. When excess tryptophan is present, a repressor In the presence of lactose and low Iucose, protein binds the operator of the trp operon the lac operon is expressed 20-fol higher and prevents the operon from being transcribed. than in the absence of lactose. In the presence of iron, the dth repressor If the sugar arabinose is present, an activator protein protein binds DNA, and the gene that encodes binds the promoter of the enes responsible for for the diphtheria toxin is not expressed. processing arabinose and in uces their transcription. In the absence of lactose, the lacR repressor protein binds the lac operon. Question 10 of 30 Arrange the following steps of the regulation of the trp operon in order of occurrence. Levels of tryptophan in the cell are low. RNA polymerase binds to the promoter. allowing transcription of the trp genes to proceed. Products of the trp genes synthesize tryptophan. Levels of tryptophan rise, and no more is required. Tryptophan binds to the trp repressor protein and induces a conformational change. The trp repressor protein binds to the operator. The trp repressor protein blocks RNA polymerase from binding to the promoter. Transcription of the trp gene stops. RNA polymerase binds to the promoter. allowing transcription of the trp genes to proceed. The trp repressor protein binds to the operator. Levels of tryptophan rise, and no more is required. Tryptophan binds to the trp repressor protein and induces a conformational change. Products of the trp genes synthesize tryptophan. The trp repressor protein blocks RNA polymerase from binding to the promoter. Question 11 of 30 The trp operon is composed of the structural genes, the promoter (P), and the operator (0). The trp repressor binds to the operator and blocks transcription. Select the image that correctly orders the three components of the trp operon and identifies, with an arrow, which component the trp repressor binds to. tip structural genes l n trp structural genes l n tip structural genes fl trp structural genes Question 12 of 30 The lac operon consists of a promoter that initiates transcription of the gene i, which encodes a repressor protein. A separate promoter, p, within the operon initiates transcription of 2, which encodes B—galactosidase, and y, which encodes permease. The operator, 0, where the repressor protein binds to inhibit transcription, is positioned between the promoter and the permease and B-galactosidase genes. The superscript u denotes uninducible mutations, whereas superscript c denotes a constitutively active mutant. The table below describes the activity of B—galactosidase and permease for haploid and diploid mutant strains. - Genotype B—galactosidase Permease _m _m absent -++++_ 3 i*p”o*z'y*/I p o z y iup+o+Z—y+/i+p+o+z+y— ll Erwocz-yvrwwzw— u i p+ 0c 2‘ y" / i+ p+ o” z” y— m constitutive Match the dominant type of regulation controlling permease expression to each mutant strain. strain 1 strain 2 strain 3 strain 4 strain 5 strain 6 J QQIHQQ Question 13 of 30 In E. coli, three structural genes, A, D, and E, encode enzymes A, D, and E, respectively. Gene 0 is an operator. The genes are in the order O-A-D-E on the chromosome and might form an operon. These enzymes catalyze the biosynthesis of valine. Mutations were isolated at the A, D, E and 0 genes to stu the production of enzymes A, D, and E when cellular levels of valine were low (T. Ramakrishnan and E. A. Adelberg, 1965. ). Levels of the enzymes produced by partial-diploid E. coli with various combinations of mutations are shown In the following table. The wild type' Is indicated with a (+), and the mutant is indicated with a (-). What type of regulator protein is binding to the operator in this possible operon'? Amcéunt of enzyme produced Genotype a repressor I---- ”a” an inducer 2 E" D” A“ 0" 35.80 38.60 46.80 an attenuator E"D+A“O+ ED+A'O'/ 4 E+o-A+o+ 35.30 38.00 Are genes A, D, and E all under control of the operator 0? No, because genotype 4 shows that gene A is controlled separately from genes E and Yes, because when the operator is nonfunctional the genes E, D, and A expression levels are high. Yes, because when the operator is functional the genes E, D, and A expression levels are high. No, because genotype 5 shows that gene E is controlled separately from genes A and Question 14 of 30 In Escherichia coli, the tryptophan operon encodes structural genes, including trpC, trpB, and trpA, that encode the tryptophan synthetase protein complex. A repressor protein encoded by the trpR gene regulates the trp operon. In the presence of high levels of tryptophan, tryptophan molecules bind the repressor protein and allow the repressor to recognize and bind to the operator, called trpO, and repress the expression of the structural tryptophan synthetase genes. In the absence of tryptophan, the repressor is unable to bind the operator and gene expression can occur. Assume any minus symbol represents a null mutant. What is the type of expression of each functional structural gene for the three bacterial strains below? trpR‘ trpO+ trpA‘ trpB+ trpC+ for trpA “0 °XPT°53i°nl for trpB constitutive for trpC constitutive J trpR" trpOC trpA“ trpB‘ trpC' no expression] constitutive repressible for trpA fly for trpB no expression | for trpC —J"° expression J trpR‘ trIDO+ trpA" trpB+trpCV Continued below... trpR+ trpO+ trpA+ trpB+ trpC— for trpA repressible] for trpB repressible] for trpC repressible Question 15 of 30 A ribozyme is an RNA catalyst. an energy storing triglyceride. a tRNA molecule. a protein enzyme. Question 16 of 30 All of the cells in the human body contain the same genes. How do cells have different morphologies and functions when they contain the same genetic information? Different cell types express particular genes at different levels. Different cell types replicate at a different rate. Different cell types obtain different types of nutrients from their surroundings. Different cell types receive different endocrine signals. Question 17 of 30 Classify each of the characteristics below as pertaining to gene regulation in either prokaryotes or eukaryotes. Prokaryotic gene regulation Eukaryotic gene regulation Genes are located on mRNA transcripts typically one chromosome. specify one protein. Some genes are or anized into operons, and mRN transcripts A 5' cap and 3' poly-A tail are often specify more than one protein. added to mRNA. mRNA can be transcribed from Transcription occurs in the DNA and translated _into protein nucleus, whereas translation at the same time. occurs in the cytoplasm. Genes are located on Some genes are or anized into mRNA can be transcribed from one chromosome. operons, and mRN transcripts DNA and translated into protein often specify more than one protein. at the same time. mRNA transcripts typically A 5' cap and 3' poly-A tail are Transcription occurs in the specify one protein. added to mRNA. nucleus, whereas translation occurs in the cytoplasm. Question 18 of 30 Select the terms that represent a mode of regulation of gene expression in eukaryotes. double-helical structure of DNA translation posttranslational modification purine ring structure mRNA splicing Question 19 of 30 Modifications to chromatin can affect transcriptional activity by changing the accessibility of DNA to the transcription machinery. Below are descriptions of various processes that may or may not cause remodeling of chromatin. Match each description to the effect it has on transcriptional activity caused by chromatin remodeling. Activates Inactivates Activates and inactivates No effect Histone Histone deacetylases Histone meth Iation A transcriptional acetyltransferases remove acetyl groups occurs at di erent activator binds an attach acetyl groups from me N-termlnus amino acids. enhancer sequence. to the N-termrnus of histones. of histones. Histone Atranscriptional Histone deacetylases Histone meth Iation acetyltransferases activator binds an remove acetyl groups occurs at di erent attach acetyl groups enhancer sequence. from me N-terminus amino acids. to the N-terminus of histones. of histones. Question 20 of 30 Identify each description as typical of eukaryotic repressors or bacterial repressors. Leave unplaced the description that is not characteristic of either group. Eukaryotic repressor Bacterial repressor binds to a silencer that uses binds to an operator downstream transcriptional activator proteins of the promoter site and to block RNA polymerase blocks RNA polymerase binds to DNA-binding motifs binds to an operator downstream on RNA polymerase and of the promoter site and directly Inhibits it blocks RNA polymerase binds to a silencer that uses transcriptional activator proteins to block RNA polymerase Question 21 of 30 Activator proteins increase gene expression, whereas repressor proteins inhibit gene expression. Which of the followrng statements concerning activator and repressor proteins In eukaryotes IS true? Eukaryotes use transcription factors instead of activators or repressors. Repressors are more common than activators in eukaryotes. Activators and repressors are equally common in eukaryotes. Activators are more common than repressors in eukaryotes. Question 22 of 30 In eukaryotes. transcription factors and enhancer sequences are used to regulate transcription. Classify the following statements as true or false. True False Enhancer sequences are Enhancer sequences can alter composed of DNA base pairs. transcripfion levels in the absence of a bound protein. Transcription factors bind to the entire enhancer sequence. Transcription factors always decrease transcription levels. Enhancer sequences can be located thousands of base pairs upstream from the transcription start site. Transcription factors bind to Enhancer sequences are the entire enhancer sequence. composed of DNA base pairs. Transcription factors always Enhancer sequences can alter decrease transcription levels. transcripfion levels in the absence of a bound protein. Enhancer sequences can be located thousands of base pairs upstream from the transcription start site. Question 23 of 30 Which of the following statements describe how inducers cause changes in gene expression? inducers allow transcription of specific genes inducers bind to activator proteins and enhance the ability of the activator to bind DNA inducers enhance transcription of all genes inducers are proteins that bind to DNA to enhance transcription of target genes inducers are ions that are essential for the function of RNA polymerase Question 24 of 30 The yeast Saccharomyces cerevisiae has several genes encoding enzymes that function in the importation and metabolism of galactose. The genes are located on several chromosomes, and are transcribed separately. The GAL genes have similar promoters, and gene transcription is under regulation by the proteins Gal3p, Gal4p, and Gal80p. Place the following statements about GAL gene regulation in the correct order, starting from conditions with an absence of galactose through conditions with abundant galactose. You will only place five statements. glucose absent. Gal4p, In complex with Qa'acmse absent Gal80p, is bound to DNA galactose becomes galactose binds Gal3p abundant Gal3p associates with Gal80p galactose binds Gal3p Gal80 inhibition of Gal p is abated i Gal4p is freed to function as an activator at GAL promoters Gal3p associates With Gal80p GALBOp is bound to DNA ¢ Gal3p interacts with Gal4p, relieving inhibition Ga|80 inhibition galactose binds continued of Gal p is abated Gal80p. inhibiting it below... Gal3p binds to promoter as an activator GFMP is freed 3° Gal4p, In complex with funwon as 3“ “twat“ Gal80p, is bound to DNA at GAL promoters i gene transcription Question 25 of 30 How do cells regulate gene expression using alternative RNA splicing? Alternative RNA splicing determines which proteins are produced from each gene. Alternative RNA splicing determines which genes are underexpressed. Alternative RNA splicing determines how fast certain proteins are degraded. Alternative RNA splicing determines which genes are transcribed to mRNA. Question 26 of 30 Each answer box represents a mechanism by which eukaryotes can regulate ene expression. Determine which of the five mechanisms each example represents. Not all examples WIII e used. Activity of Changes in transcription Initiation of chromatin structure apparatus RNA processing RNA interference translation Meth lation of Initiation of The 3' end can be The RISC degrades RNA granules Cp islands transcription _ cleaved to produce mRNA complexed control the represses promoter occurs u on binding different transcript with miRNA availability of actiVIty. of T IID at lengths before or siRNA. mRNA or the TATA box. addition of translation. the poly-A tail. The 3' end can be RNA granules Meth lation of Gene inversion cleaved to produce control the Cp islands does not cause different transcript availability of represses promoter a loss of genetic lengths before mRNA or actiVIty. information addition of translation. but may affect the poly-A tail. regulation of the inverted genes. Initiation of The RISC degrades transcription mRNA complexed occurs u on binding with miRNA of T IID at or siRNA. the TATA box. Question 27 of 30 Drosophila sex determination involves the regulation of alternative RNA splicing by the sex-lethal (le), transformer (tra), and doublesex (dsx) genes. Match each effect on Drosophila sexual development with the gene deletion that would cause it. le deletion tra deletion dsx deletion male-specific splicing male-specific splicing absence of female-determining of tra yields male of dsx yields male regulatory protein yields traits in females traits In females male traits in females absence of male-determining regulatory protein yields female traits in males male-specific splicing absence of female-determining male-specific splicing of tra yields male regulatory protein yields of dsx yields male traits in females male traits in females traits In females absence of male-determining regulatory protein yields female traits in males Question 28 of 30 How can microRNAs (miRNAs) regulate gene expression? prevent transcription by binding to DNA and removing transcription factors prevent transcription by binding to RNA polymerase and stopping RNA production prevent translation by binding to mRNA and degrading the mRNA strand prevent translation by binding to tRNA and interfering with protein synthesis Question 29 of 30 In Arabidopsis thaliana, the Flowering Locus C (FLC) gene codes for a regulatory protein that suppresses flowering. FLC is expressed in seedlings to prevent premature flowering. In mature plants, FLC expression decreases with cooler temperatures, and flowering occurs once sufficiently cool temperatures are reached. If small-interferin RNA (siRNA) that is complementary to FLC mRNA is introduced, how would RNA interference (RN i) affect flowering? RNAi would induce methylation of chromatin and repress flowering. RNAi is found in prokaryotes and would not affect Arabidopsis. RNAi would degrade FLC mRNA and stimulate flowering. RNAi would degrade FLC mRNA and repress flowering. RNAi would bind irreversibly to FLC mRNA and stimulate flowering. Question 30 of 30 Which description applies to post-translational gene regulation? mRNA modifications such as additions of a 5' cap and 3' poly-A tail and removal of introns heritable changes in gene expression that occur without altering the DNA sequence protein modifications such as addition of a functional group, or structural changes such as folding a gene cluster controlled by a single promoter that transcribes to a single mRNA strand processing of exons in mRNA that results in a single gene coding for multiple proteins ...
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