In the Avery experiment, mice were killed if they injected with S strain cells. Furthermore, incubation with extract from dead S strain cells could transform non pathogenic cells into pathogenic cells. This effect of S strain extract was eliminated if S strain extract is treated with what enzyme before incubation with non-pathogenic cells? protease DNAse RNAse Lipase
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In the Avery experiment, mice were killed if they injected with S strain cells. Furthermore, incubation with extract from dead S strain cells could transform non pathogenic cells into pathogenic cells. This effect of S strain extract was eliminated if S strain extract is treated with what enzyme before incubation with non-pathogenic cells?
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- Consider the biochemical pathway shown here. Suppose that a strain of bacteria must synthesize compound 4 to survive and divide. Successful survival and division of bacteria is observed as growth of colonies on an agar plate. This strain of bacteria can grow colonies on minimal medium as long as it is supplemented with compound 1. You are in a lab that has isolated several mutants of this strain. You find that these mutants cannot grow on minimal medium supplemented with compound 1, though they can grow colonies if supplemented with compound 4. Considering what you know about the Beadle-Tatum experiments, which of the following statements would be one that should be true?B-lactamase is an enzyme found in many antibiotic-resistant bacteria that hydrolyzes and inactivates antibiotics like penicillin and cephalosporin. The amount of antibiotic hydrolyzed in 1 minute in a 10-ml solution containing purified ß-lactamase was measured as a function of antibiotic concentration. The kinetics of hydrolysis was performed for two antibiotic substrates (A and B). Assume that the concentration of ß-lactamase was kept constant during the assay. 12 Initial Velocity (nanomole/min) 10 8 2 0 10 20 | 30 [Antibiotic] (µm) 40 50 Antibiotic A Antibiotic B a) Based on the enzyme description, what type of enzyme is ß-lactamase? Lyase Isomerase Ligase Hydrolase Oxidoreductase Transferase b) Based on your answer in (a), what other reactant, in addition to the antibiotic substrate, needs to be in the active site of ß-lactamase for the hydrolysis reaction to proceed? c) From the reaction curves above, what is the approximate value of Vmax for the enzyme reaction? (Do not forget the…Sydney Brennen isolated Salmonella typhimurium mutants that were implicated in the biosynthesis of tryptophan and would not grow on minimal medium supplemented with intermediates in tryptophan biosynthesis, some mutants were able to grow while others remained unable to grow. Review the data attached to order the biosynthetic pathway by both enzymatic step and by intermediate biomolecule. Label the step impacted by each of the mutant cell lines.
- The purified OXA-M290 enzyme can now be tested to determine which β-lactamase inhibitor is most effective. This inhibitor could be prescribed in combination with a β-lactam antibiotic to treat the infection caused by the E. coli KGH1 strain. Before testing inhibitors against OXA-M290, the kinetic activity of this enzyme must first be measured. The activity of OXA-M290 is measured using nitrocefin, a chromogenic β-lactam antibiotic. When nitrocefin is hydrolyzed by a β-lactamase, it changes from yellow to red in colour. The nitrocefin hydrolysis product has an extinction coefficient of 20,500 M-1 cm-1 at 486 nm. The hydrolysis of 60 μM nitrocefin by 1 nM OXA-M290 is monitored using a microplate reader. The absorbance of the wells in the plate is measured at 486 nm every 30 seconds. This experiment is carried out with three replicates, generating the following data: Time (min) Absorbance of Replicate 1 Absorbance of Replicate 2 Absorbance of Replicate 3 0.5 0.0984…Pyridoxal phosphate (PLP) is a coenzyme for the enzyme ornithine aminotransferase. The enzyme was purified from cells grow in PLP = deficient media as well as from cells grown in media that contained pyridoxal phosphate. The stability of the two different enzyme preparations was then measured by incubating the enzyme at 37°C for different lengths of time and then assaying for the amount of enzyme activity remaining. The following results were obtained. (a) Why does the amount of active enzyme decrease with the time of incubation? (b) Why does the amount of enzyme from the PLP deficient cells decline more rapidly?The substrate which was used to investigate the enzymatic activity of wheat bran phosphatase was p-nitrophenyl phosphate. It is converted to p-nitrophenol and inorganic phosphate by this enzyme. P-nitrophenol has a pKa of 7.1 and is colorless, while its conjugate base, p-nitrophenolate has a yellow color. The enzyme assay was performed at pH 5.1 after the 0.5 N KOH is added at the end of each enzyme assay, the pH of the assay mixture is raised to 9.1. Why was the base added?
- You perform Michaelis-Menten kenetics on i) trypsin and ii) a mutant form of the same enzyme (a single amino acid has been changed). The specificity constant for the mutant was 10 times larger than for trypsin. a) Define the specificity constant and explain using this definition how a larger value might occur. b) Explain how, if at all, a non-competitive inhibitor of trypsin would affect the specificity constant.Anan enzyme isolated from a mutant bacterium grown at 20°C works in a test tube at 20°C but not at 37°C (37°C is the temperature of the gut, where this bacterium normally lives). furthermore, once the enzyme has been exposed to the higher temperature, it no longer works at the lower one. The same enzyme isolated from the normal bacterium works at both temperatures. can you suggest what happens (at the molecular level) to the mutant enzyme as the temperature increases?Clary Leonhart used the pET vector system to express her prokaryotic amylase enzyme. She added peptone into her culture broth of BL21 (DE3) Escherichia coli strain. At the end of the experiment, she discovered that her protein was not expressed. She repeated three more times but her protein of interest was still not produced. (i) (ii) Explain the reason why Clary failed to obtain her protein of interest and suggest a solution to troubleshoot this problem. Clary plans to express her protein along with a polyhistidine-tag, or better known by its trademarked name IIis-tag. Explain the importance of His-tag in protein work.
- A classic way to isolate thymidylate synthase–negative mutants of bacteriais to treat a growing culture with thymidine and trimethoprim. Most ofthe cells are killed, and the survivors are greatly enriched in thymidylatesynthase–negative mutants.(a) What phenotype would allow you to identify these mutants?(b) What is the biochemical rationale for the selection? (That is, why are themutants not killed under these conditions?)(c) How would the procedure need to be modified to select mammalian cellmutants defective in thymidylate synthase?A number of auxotrophic mutant strains were isolated from wild-type haploid Neurospora crassa. These strains responded to the addition of certain nutritional supplements to minimal culture medium either by growth (+) or no growth (0) The data from this experiment are presented in the table below. Diagram a biochemical pathway, complete with positions of intermediates, that is consistent with the data. Indicate where in the pathway each mutant strain is blocked.What features distinguish enzymes that undergo allosteric control from those that obey Michaelis-Menten equations? Give 2 differences