Concept explainers
Synthesis of the amino acid histidine is a multistep anabolic pathway that uses the products of
a. Why is growth observed in experiment
b. What is the genotype of exconjugants in experiment 2?
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Study Guide And Solutions Manual For Genetic Analysis: An Integrated Approach
- Homologous Recombination, Heteroduplex DNA, and Mismatch Repair Homologous recombination in E. coli leads to the formation of regions of heteroduplex DNA. By definition, such regions contain mismatched bases. Why doesn’t the mismatch repair system of E. coli eliminate these mismatches?arrow_forwardThe Enzymatic Activities of DNA Polymerase I (a) What are the respective roles of the 5 -exonudease and 3 -exonuclease activities of DNA polymerase I? (b) What might be a feature of an E. coli strain that lacked DNA polymerase I 3 -exonuclease activity?arrow_forwardHelicase Unwinding of the E. coli Chromosome Hexameric helicases, such as DnaB, the MCM proteins, and papilloma virus El helicase (illustrated in Figures 16.22 to 16.25), unwind DNA by passing one strand of the DNA duplex through the central pore, using a mechanism based on ATP-dependent binding interactions with the bases of that strand. The genome of E. coli K12 consists of 4,686,137 nucleotides. Assuming that DnaB functions like papilloma virus El helicase, from the information given in Chapter 16 on ATP-coupled DNA unwinding, calculate how many molecules of ATP would be needed to completely unwind the E. coli K 12 chromosome.arrow_forward
- Heteroduplex DNA Formation in Recombination From the information in Figures 28.17 and 28.18, diagram the recombinational event leading to the formation of a heteroduplex DNA region within a bacteriophage chromosome.arrow_forwardScientists who study amino acid biosynthesis pathwayswant to isolate auxotrophic bacteria. A technique calledpenicillin enrichment makes this task easier. This procedure starts by exposing a liquid culture of wild-type (prototrophic) bacteria growing in rich (complete)medium to a chemical mutagen. After this treatment,the cells are centrifuged to remove the liquid and themutagen. The pellet of cells at the bottom of the centrifuge tube is now resuspended in medium that lacksone amino acid (in this example, cysteine) but contains penicillin. Subsequently, the bacteria are pouredonto a filter that concentrates them and allows themto be washed free of the penicillin. The living bacteriaretained on the filter are highly enriched for cysteineauxotrophs.a. Given what you know about the action of pencillin,explain why this enrichment occurs.b. Penicillin enrichment is not a selection, becausethe drug does not kill 100% of the prototrophs.The cells on the filter thus need to be screenedfor…arrow_forwardDescribe how the association of DNMT1 with the UHRF1 and PCNA proteins ensures that it will be found on hemimethylated DNA.arrow_forward
- In E. coli, a methyltransferase enzyme encoded by the dam generecognizes the sequence 5′–GATC–3′ and attaches a methyl groupto the nitrogen at position 6 of adenine. E. coli strains that have thedam gene deleted are known to have a higher spontaneous mutationrate than normal strains. Explain why.arrow_forwardAs an onion and burger lover, your friend would like to incorporate the cheems gene (“cheM”) from the rare Shiba Inu into sweet onions, in order to perfect the vegetable’s viability as a hamburger ingredient. To do so, she plans to clone the cheM gene (with an eukaryotic promoter) into the dOge plasmid. The dOge plasmid is capable of replicating in E. coli and also contains an ampicillin resistance gene, under a prokaryotic promoter, as a selective marker. Then, she plans to perform a trans-domain conjugation between E. coli (containing the plasmid with the cheM gene) and onion cells. However, you are not confident that this project will be successful, and point out some issues with the overall methodology. Identify two issues that will not allow the onion to express the cheM gene, based on the overall methodology described above.arrow_forwardA site-directed mutagenesis experiment was done on the catalytic triad of the serine protease subtilisin where all of the amino acids of the catalytic triad were mutated to alanine. The triple mutant enzyme was characterized kinetically and the mutant displayed a thousand-fold (103) rate enhancement over the uncatalyzed reaction. Explain the source of this rate enhancement. (The native wild-type subtilisin has a rate acceleration of 1010, when compared to the uncatalyzed reaction.)arrow_forward
- DNA polymerase I (Pol I) of E. coli consists of three functional parts (domains): an N-terminal domain with 5´ to 3´ exonuclease activities required for removal of the RNA primer, a central domain responsible for 3´ to 5´ exonuclease proofreading, and a C-terminal domain with polymerase activity. Pol I is thought to simultaneously remove RNA primers and fill in the gaps that result. A group of proteins known as RNaseH also have 5´ to 3´ exonuclease activity and can thus remove RNA primers. However, they lack the other two functions observed for Pol I. Predict the ability of the following mutants to replicate DNA: (1) a strain with a mutant gene encoding Pol I such that it no longer has polymerase activity (but retains both types of nuclease activities); (2) a strain without RNaseH proteins; (3) a strain with a mutant gene encoding Pol I such that it no longer has 5´ to 3´ exonuclease activities (but retains 3´ to 5´ nuclease and polymerase activities); (4) a strain with…arrow_forwardThe SARS-CoV-2 genome has a cap at its 5'-end that is the same as the one seen on most human mRNA molecules. The nsp12 RNA-dependent RNA polymerase acts like cellular RNA polymerase and initiates RNA synthesis by synthesizing a dinucleotide from two nucleoside triphosphates. What other enzymes are needed to add a cap to the nsp12 product? Describe the chemical nature of the products of each of these enzymesarrow_forwardAlthough a large number of mutagenic chemicals are known,none is known that induces mutations in only a single gene(gene-specific mutagenesis). From what you know aboutmutagens, explain why it is unlikely that a gene-specificchemical mutagen will be found. How then is site-specificmutagenesis accomplished?arrow_forward
- BiochemistryBiochemistryISBN:9781305577206Author:Reginald H. Garrett, Charles M. GrishamPublisher:Cengage Learning