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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Genetic Analysis: An Integrated Approach (2nd Edition)
- In a cotransformation experiment (see question 4 of More GeneticTIPS), DNA was isolated from a donor strain that was proA+ andstrC+ and sensitive to tetracycline. (The proA and strC genes conferthe ability to synthesize proline and confer streptomycin resistance,respectively.) A recipient strain is proA− and strC− and isresistant to tetracycline. After transformation, the bacteria werefirst streaked on a medium containing proline, streptomycin, andtetracycline. Colonies were then restreaked on a medium containingstreptomycin and tetracycline. (Note: Each type of medium hadcarbon and nitrogen sources for growth.) The following resultswere obtained:70 colonies grew on the medium containing proline, streptomycin,and tetracycline, but only 2 of these 70 colonies grew whenrestreaked on the medium containing streptomycin and tetracyclinebut lacking proline. If we assume the average size of the DNA fragments is 2 minutes,how far apart are these two genes?arrow_forwardAll are correct about DNA gyrase in E. coli EXCEPT: It works to remove positive supercoiling introduced by the DnaB protein (helicase). It is a topoisomerase that hydrolyzes ATP during its reaction mechanism. Its mechanism involves the breaking of a single phosphoester bond in one strand of dsDNA. It works to relieve supercoiling in DNA to overcome the torsion stress imposed upon unwinding.arrow_forwardThe following shows the genotype of a partial diploid bacterial cell - where one chromosomal region containing the lac operon in E,coli is given, and the other fragment is from a plasmid carrying another lac operon from another source. The two are separated by a slash (/). The possible answers indicate with a ʺ+ʺ or a ʺ-ʺ whether β-galactosidase would be expected to be produced at induced levels under two circumstances: 1) first in the absence of lactose and 2) second in the presence of lactose. (Assume that glucose is not present in the medium.)Genotype F: I+ Oc Z-/ Fʹ I- O+ Z+ KEY:I+ = wild-type repressorI- = mutant repressor (unable to bind to the operator)Is = mutant repressor (insensitive to lactose)O+ = wild-type operatorOc = constitutive operator (insensitive to repressor)arrow_forward
- Telomerase activity has been found to be 10 to 20 times more active in cancer cells than in normal somatic cells. What is the significance of this circumstance?arrow_forwardexplain please: Spike-Driven Syncytia Formation Is Coupled to S20 Fragment Generation in the Presence of ACE2. To investigate the functional and biochemical signatures of spike (S) protein upon engaging its receptor ACE2 in live cells, we first utilized a cell–cell fusion assay to obtain potentially cleaved spike protein products from syncytia . In this system, HEK293T cells transfected with plasmids encoding WT spike readily formed syncytia after coculturing with HEK293T cells expressing human and Vero E6-ACE2, as well as colorectal adenocarcinoma Caco-2 and lung adenocarcinoma Calu-3 cells expressing endogenous ACE2. We then collected these adherent syncytia and immunoblotted for cleaved spike species using a rabbit polyclonal antibody specifically detecting the S2 ectodomain through standard reducing Tris-glycine sodium dodecyl sulfate polyacrylamide gel electrophoresis. This experiment revealed that spike expression in HEK293T cells displayed full-length S and autocleaved S2…arrow_forwardA plasmid vector pBS281 is cleaved by the enzymeBamHI (5′ G^GATCC 3′), which recognizes only onesite in the DNA molecule. Human DNA is digestedwith the enzyme MboI (5′ ^GATC 3′), which recognizes many sites in human DNA. These two digestedDNAs are now ligated together. Consider only thosemolecules in which the pBS281 DNA has been joinedwith a fragment of human DNA. Answer the following questions concerning the junction between thetwo different kinds of DNA. a. What proportion of the junctions between pBS281and all possible human DNA fragments can becleaved with MboI?b. What proportion of the junctions between pBS281and all possible human DNA fragments can becleaved with BamHI?c. What proportion of the junctions between pBS281and all possible human DNA fragments can becleaved with XorII (5′ C^GATCG 3′)?d. What proportion of the junctions between pBS281and all possible human DNA fragments can becleaved with BstYI (5′ R^GATCY 3′)? (R and Ystand for purine and pyrimidine, respectively.)e.…arrow_forward
- A number of yeast-derived elements were added to thecircular bacterial plasmid pBR322. Yeast that requireuracil for growth (Ura− cells) were transformed withthese modified plasmids and Ura+ colonies were selected by growth in media lacking uracil. For plasmidscontaining each of the elements listed in parts (a) to(c), indicate whether you expect the plasmid to integrate into a chromosome by recombination, or insteadwhether it is maintained separately as a plasmid. If theplasmid is maintained autonomously, is it stably inherited by all of the daughter cells of subsequent generations when you no longer select for Ura+ cells (that is,when you grow the yeast in media containing uracil)?a. URA+ geneb. URA+ gene, ARS c. URA+ gene, ARS, CEN (centromere)d. What would need to be added in order for these sequences to be maintained stably in yeast cells as alinear artificial chromosome?arrow_forwardConsider the structure of Cro repressor protein from bacteriophage lambda E. It is a DNA binding protein, and like many sequence- specific DNA binding proteins, it must function as a homodimer Ex. Notice the mutual docking of a phenylalanine residue from each subunit into a hydrophobic pocket of the partner subunit. These hydrophobic interactions are required for dimerization. The noncovalent interactions highlighted in yellow are also required for dimerization. These interactions represent examples of: Osecondary structure O tertiary structure O quaternary structure O secondary AND quaternary structure Ⓒ tertiary AND quaternary structurearrow_forwardExplain the structural activity between trans-ferulic acid and the NS2B-NS3 protease in the DENV-2 strain? Please refer to the specific conserved domains affected in the NS2B-NS3 Protease by trans ferric acid and how trans ferric acid can prevent viral replication by inhibiting the activity of the NS2B-NS3 protease in DENV-2.arrow_forward
- Suppose you have six strains of E. coli. One is wildtype, and each of the other five has a single one of thefollowing mutations: lacZ−, lacY−, lacI−, oc, andlacIS. For each of these six strains, describe thephenotype you would observe using the following assays. [Notes: (1) IPTG is a colorless synthetic molecule that acts as an inducer of lac operon expressionbut cannot serve as a carbon source for bacterialgrowth because it cannot be cleaved byβ-galactosidase; (2) X-gal cannot serve as a carbonsource for growth; (3) E. coli requires active lactosepermease (the product of lacY) to allow lactose,X-gal, or IPTG into the cells.] Colony color in medium containing glycerol as theonly carbon source and X-gal, but no IPTG.d. Colony color in medium containing high levels ofglucose as the only carbon source, X-gal, andIPTG.e. Colony color in medium containing high levels ofglucose as the only carbon source and X-gal, butno IPTGarrow_forwardWhen Zidovudine (3'-azidothymidine or AZT) is added directly to an assay measuring the rate of DNA synthesis catalyzed by the AIDS virus reversed transcriptase, AZT is shown to be without significant inhibitory activity. Explain how AZT is metabolized in virus infected cells to convert the nucleoside into a potent and effective reversed transcriptase inhibitor.arrow_forwardBudding yeasts such as S. cerevisiae exhibit telomerase activity throughout their life cycles, whereas human somatic cells do not exhibit telomerase activity. Suggest why this is so.arrow_forward
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