You are studying the ABCD operon from a newly isolated bacterium. Which of the following would result in expression of proteins A, B, and C but not D? C promoter Mutation in D that causes degradation of the mRNA Mutation in A that removes the translational start site All of these options Mutation of sequences in the promoter needed for RNA Polymerase to bind Insertion of a transcriptional termination site in the beginning of the D sequence

You are studying the ABCD operon from a newly isolated bacterium. Which of the following would result in expression of proteins A, B, and C but not D? C promoter Mutation in D that causes degradation of the mRNA Mutation in A that removes the translational start site All of these options Mutation of sequences in the promoter needed for RNA Polymerase to bind Insertion of a transcriptional termination site in the beginning of the D sequence

Human Anatomy & Physiology (11th Edition)

11th Edition

ISBN:9780134580999

Author:Elaine N. Marieb, Katja N. Hoehn

Publisher:Elaine N. Marieb, Katja N. Hoehn

Chapter1: The Human Body: An Orientation

Section: Chapter Questions

Problem 1RQ: The correct sequence of levels forming the structural hierarchy is A. (a) organ, organ system,...

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You are studying an operon containing three genesthat are cotranscribed in the order hupF, hupH, andhupG. Diagram the mRNA for this operon, showingthe location of the 5′ and 3′ ends, all open readingframes, translational start sites, stop codons, transcription termination signals, and any regions thatmight be in the mRNA but do not serve any of thesefunctions.
One of the main lessons of this chapter is that severalbacterial genes are often transcribed from a singlepromoter into a large multigene (polycistronic) transcript. The region of DNA containing the set of genesthat are cotranscribed, along with all of the regulatoryelements that control the expression of these genes, iscalled an operon.a. Which of the mechanisms in the following listcould explain differences in the levels of themRNAs for different operons?b. Which of the mechanisms in the following listcould explain differences in the levels of theprotein products of different genes in the sameoperon?i. Different promoters might have different DNAsequences.ii. Different promoters might be recognized bydifferent types of RNA polymerase.iii. The secondary structures of mRNAs might differ so as to influence the rate at which they aredegraded by ribonucleases.PROBLEMSProblems 575a. Why did the mating with a nonlysogenic recipientresult in phage growth and release, but the infectionof a…
Suppose that you have isolated a mutant strain of E. coli inwhich the lac operon is constitutively expressed. To understandthe nature of this defect, you create a merozygote in which themutant strain contains an F′ factor with a normal lac operonand a normal lacI gene. You then compare the mutant strain andthe merozygote with regard to their β-galactosidase activities inthe presence and absence of lactose. You obtain the followingresults:
. In an effort to determine the location of an operator sitefor a negatively regulated gene, you have made a seriesof deletions within the regulatory region. The extent ofeach deletion is shown by the line underneath the sequence, and the resulting expression from the operon(i = inducible; c = constitutive; − = no expression) isalso indicated.... GGAT C T T AGCCGGCTAACATGATAAATATAA......C C T AGAATCGGCCGA TTGTA C T A TTT ATAT T ...1 i2 –3 c4 –5 ca. What can you conclude from these data about thelocation of the operator site?b. Why do you think deletions 2 and 4 show no expression of the gene?
Mutations in bacterial promoters may increase or decrease therate of gene transcription. Promoter mutations that increasetranscription are termed up-promoter mutations, and those thatdecrease transcription are termed down-promoter mutations.The sequence of the −10 site of the promoter for the lac operonis TATGTT (see Figure 14.5). Would you expect each of thefollowing mutations to be an up-promoter or down-promotermutation?A. TATGTT to TATATTB. TATGTT to TTTGTTC. TATGTT to TATGAT
The promoter of an operon is the site to which RNApolymerase binds to begin transcription. Certain basechanges in the promoter result in a mutant site towhich RNA polymerase cannot bind. Would you expect mutations in the promoter that prevent binding ofRNA polymerase to act in trans on another copy ofthe operon on a plasmid in the cell, or only in cis onthe copy immediately adjacent to the mutated site?
Lactose permease is encoded by the lacY gene of the lac operon.Suppose a mutation occurred at codon 64 that changed the normalglycine codon into a valine codon. The mutant lactose permease isunable to function. However, a second mutation, which changescodon 50 from an alanine codon to a threonine codon, is able torestore function. Is each of the following terms appropriate or inappropriate to describe this second mutation?A. ReversionB. Intragenic suppressorC. Intergenic suppressorD. Missense mutation
Scientists have exploited the siRNA pathway toperform a technique called RNA interference—ameans to knock down the expression of a specificgene without having to make mutations in it. Theidea is to introduce dsRNA corresponding to thetarget gene into an organism; the dsRNA is thenprocessed into an siRNA that leads to the degradation of the target gene’s mRNA. One clever methodfor delivery of the dsRNA to some organisms (thenematode C. elegans, for example) is to feed thembacteria transformed with a recombinant plasmidthat expresses dsRNA.a. Draw a gene construct that, when expressed from aplasmid in bacteria, could be used to knock downby RNA interference the expression of gene X ofC. elegans.b. How can you test if gene X expression is obliterated in worms that have eaten the bacteria transformed with a plasmid containing your construct?c. Do you think that only gene X expression will beaffected in these worms? Explain.
The symbols a, b, and c in the table below represent theE. coli lac system genes for the repressor (I ), the operator(O) region, and the β-galactosidase (Z), although notnecessarily in that order. Furthermore, the order inwhich the symbols are written in the genotypes is notnecessarily the actual sequence in the lac operon.Activity (+) or inactivity (−) of Z geneGenotype Inducer absent Inducer presenta- b+ c+ + +a+ b+ c- + +a+ b- c- - a+ b- c+/a- b+ c- + +a+ b+ c+/a- b- c- - +a+ b+ c-/a- b- c+ - +a- b+ c+/a+ b- c- + +a. Which symbol (a, b, or c) represents each of the lacgenes I, O, and Z ?b. In the table, a superscript minus sign on a gene symbolmerely indicates a mutant, but some mutant behaviorsin this system are given special mutant designations.Using the conventional gene symbols for the lac operon,designate each genotype in the table.
Bacterial DNA containing an operon encoding three enzymes is introduced into chromosomal DNA in yeast (a eukaryote) in such a way that it is properly flanked by a promoter and a transcriptional terminator. The bacterial DNA is transcribed and the RNA correctly processed, but only the protein nearest the promoter is produced. Can you suggest why?
Attenuation of the trp operon is regulated by the efficiency of translation of the trp leader (trpL).A scientist mutates the aminoacyl tRNA synthetase responsible for charging tRNATrp, resulting in1/100 the normal amount of charged tRNATrp. How would this mutation impact attenuation ofthe trp operon? Explain why.
Based on its sequence similarity to Apobec1,which deaminates Cs to Us in RNA, activation-induceddeaminase (AID) was originally proposed to work on RNA.But definitive experiments in E. coli demonstrated thatAID deaminates Cs to Us in DNA. The authors of the paperexpressed AID in bacteria and followed mutations in aselectable gene. They found that AID expression increasedmutations about fivefold above the background level inthe absence of AID expression. More importantly, theyfound that 80% of the induced mutations were G→A orC→T. Does this fit with your expectation if AID-inducedmutations arose by deamination of C to U in the DNA?