Brenner’s m mutant phages (m1–m6) described inFig. 8.8 were suppressed when grown in suppressor(su−) mutant bacteria; they produced full-length Mproteins that functioned like wild-type M protein.a. What gene do you think was mutant in the su−bacteria?b. When the m− phages were propagated in the su−bacterial strain, not all of the proteins made by themutant m alleles were identical to wild-type Mprotein. How did some of them differ?

Brenner’s m mutant phages (m1–m6) described inFig. 8.8 were suppressed when grown in suppressor(su−) mutant bacteria; they produced full-length Mproteins that functioned like wild-type M protein.a. What gene do you think was mutant in the su−bacteria?b. When the m− phages were propagated in the su−bacterial strain, not all of the proteins made by themutant m alleles were identical to wild-type Mprotein. How did some of them differ?

Biology: The Dynamic Science (MindTap Course List)

4th Edition

ISBN:9781305389892

Author:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Publisher:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Chapter15: From Dna To Protein

Section15.1: The Connection Between Dna, Rna, And Protein

Problem 1SB

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The bacteriophage genome consists of many genes encoding proteins that make up the head, collar, tail, and tail fibers. When these genes are transcribed following phage infection, how are these proteins synthesized, since the phage genome lacks genes essential to ribosome structure?
In Hershey-Chase experiment, bacteriophages protein coats were tagged with radioactive isotope S-32. These phages were used to infect E. coli cells and the cells were further centrifuged to form pellets. Why was the radioactivity level of S-32 found greater outside the cells compared to the E. coli cell pellets? Explain briefly. If the experiment is repeated in the same manner but this time the phage protein coats are labelled with isotope X and the phage DNA with isotope Y, which isotope’s radioactivity will be found in greater amounts in the E. coli cell pellets after centrifugation? Explain briefly.
The bacteriophage genome consists primarily of genes encodingproteins that make up the head, collar and tail, and tail fibers When these genes are transcribed following phage infection, howare these proteins synthesized, since the phage genome lacksgenes essential to ribosome structure?
By conducting conjugation experiments between Hfr and recipientstrains, Wollman and Jacob mapped the order of many bacterialgenes. Throughout the course of their studies, they identified severaldifferent Hfr strains in which the F-factor DNA had been integratedat different places along the bacterial chromosome. A sample of theirexperimental results is shown in the table:Draw a map that shows the order of genes and the locations ofthe origins of transfer among these different Hfr strains?
Researchers have been determining the nucleotide sequences of variant forms of SARS-CoV-2, looking for versions of the virus that might be more easily transmitted between humans or that might be more deadly. (a) For example, one mutation in a viral gene changed a GAU codon to a GGU codon. How does this change affect the sequence of the polypeptide encoded by that gene? (b) In another variant form of the virus, a gene is missing six consecutive nucleotides. How would this change affect the sequence of the polypeptide encoded by that gene? (c) In another coronavirus variant, the spike protein (the prominent protein on the surface of the virus) contains a histidine residue where an aspartate (aspartic acid) residue should be. Describe a point mutation in the coronavirus genome that could have caused this change in the spike protein.
Austin Taylor and Edward Adelberg isolated some new strains of Hfr cells that they then used to map several genes in Escherichia coli by using interrupted conjugation. In one experiment, the researchers mixed cells of Hfr strain AB‑312, which were xyl+ mtl+ mal+ met+ and sensitive to phage T6, with F− strain AB‑531, which was xyl− mtl− mal− met− and resistant to phage T6. The cells were allowed to undergo conjugation. At regular intervals, the researchers removed a sample of cells and interrupted conjugation by killing the Hfr cells with phage T6. The F− cells, which were resistant to phage T6, survived and were then tested for the presence of genes transferred from the Hfr strain. The results of this experiment are shown in the graph. On the basis of these data, give the order of the xyl, mtl, mal, and met genes on the bacterial chromosome and the minimum distances between them in minutes. The origin of transfer is represented by the red triangle. The distances between genes are not…
In a generalized-transduction experiment, phages arecollected from an E. coli donor strain of genotype cys+leu+ thr+ and used to transduce a recipient of genotypecys- leu- thr-. Initially, the treated recipient populationis plated on a minimal medium supplemented with leucine and threonine. Many colonies are obtained.a. What are the possible genotypes of these colonies?b. These colonies are then replica plated onto threedifferent media: (1) minimal plus threonine only, (2)minimal plus leucine only, and (3) minimal. Whatgenotypes could, in theory, grow on these three media?c. Of the original colonies, 56 percent are observed togrow on medium 1, 5 percent on medium 2, and nocolonies on medium 3. What are the actual genotypes ofthe colonies on media 1, 2, and 3?d. Draw a map showing the order of the three genes andwhich of the two outer genes is closer to the middle gene
When 1 million cells of a culture of haploid yeastcarrying a met− auxotrophic mutation were plated onpetri plates lacking methionine (Met), five coloniesgrew. You would expect cells in which the originalmet− mutation was reversed (by a base change back tothe original sequence) would grow on the media lackingmethionine, but some of these apparent reversions couldbe due to a mutation in a different gene that somehowsuppresses the original met− mutations. How wouldyou be able to determine if the mutations in your fivecolonies were due either to a precise reversion of theoriginal met− mutation or to the generation of a suppressor mutation in a gene on another chromosome?
The genetic alteration responsible for sickle-cell anemia in humans involves: a transition mutation from A to G, substituting glutamic acid for valine in a-globin a transversion mutation from T to A, substituting valine for glutamic acid in b-globin a transition mutation from T to C, substituting valine for glutamic acid in b-globin a transversion mutation from G to C, substituting glutamic acid for valine in a-globin a frameshift mutation of one ATC codon, removing glutamic acid from b-globin
In 1965, Jon Beckwith and Ethan Signer devised a method of obtaining specialized transducing phages carrying the lac region. They knew that the integration site, designated att80, for the temperate phage φ80 (a relative of phage λ) was located near tonB, a gene that confers resistance to the virulent phage T1: tonB att80 They used an F ′ lac+ plasmid that could not replicate at high temperatures in a strain carrying a deletion of the lac genes. By forcing the cell to remain lac+ at high temperatures, the researchers could select strains in which the plasmid had integrated into the chromosome, thereby allowing the F ′ lac to be maintained at high temperatures. By combining this selection with a simultaneous selection for resistance to T1 phage infection, they found that the only survivors were cells in which the F ′ lac had integrated into the tonB locus, as shown here: tonB F lac att80 This result placed the lac region near the integration site for phage φ80. Describe the subsequent…
Austin Taylor and Edward Adelberg isolated some new strains of Hfr cells that they then used to map several genes in E. coli by using interrupted conjugation . In one experiment, they mixed cells of Hfr strain AB-312, which were xyl+ mtl+ mal+ met+ and sensitive to phage T6, with F− strain AB-531, which was xyl− mtl− mal− met− and resistant to phage T6. The cells were allowed to undergo conjugation. At regular intervals, the researchers removed a sample of cells and interrupted conjugation by killing the Hfr cells with phage T6. The F− cells, which were resistant to phage T6, survivedand were then tested for the presence of genes transferred from the Hfr strain. The results of this experiment are shown in the accompanying graph. On the basis of these data, give the order of the xyl, mtl, mal, and met genes on the bacterial chromosome and indicate the minimum distances between them.
You learned in Problem 21 in Chapter 7 that theneurodegenerative disease ALS can be caused by expansion of a hexanucleotide repeat region (5′-GGGGCC-3′)outside of the open reading frame (but within the firstintron) of the gene called C9ORF72. While a normalC9ORF72 allele has 2–23 copies of the hexanucleotiderepeat unit, dominant disease-causing alleles have hundreds or even thousands of copies. Researchers observed that the first intron of theC9ORF72 disease allele is transcribed not only fromthe normal template strand of DNA, but also from thenontemplate strand. Even more unusual, both types ofrepeat-region transcripts are translated in all six readingframes in an AUG-independent manner—a processcalled repeat-associated non-ATG translation, or RANtranslation. These discoveries led to the hypothesisthat the proteins made from the repeats mightcontribute to ALS.a. What polypeptides are made from the repeat-regiontranscripts?b. According to the RAN translation hypothesis, whyare…