Some bacteria contain three different forms of aspartokinase, each with its own mode of regulation. Based on the roles of aspartoki- nase, as discussed in the text, propose a regulatory scheme applicable to each form of aspartokinase.
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- In a certain bacterial species, the amino acid arginine is synthesized by a particular enzyme so the bacterium does not require arginine in its growth medium. A key enzyme, which we will call arginine synthetase, is necessary for arginine biosynthesis. When these bacteria are given arginine in their growth media, they stop synthesizing arginine intracellularly. Based on this observation alone, propose three different regulatory mechanisms to explain why arginine biosynthesis ceases when arginine is added to the growth medium. To better understand the mechanism of regulation, you measure the amount of intracellular arginine synthetase protein when cells are grown in the presence and absence of arginine. Under both growth conditions, the amount of this protein is identical. Which mechanism of regulation would be consistent with this experimental observation?.Bacterial species that are capable of synthesising the amino acid histidine do not need it in their growth medium. Histidine biosynthesis requires a specific enzyme, which we shall refer to as histidine synthetase. When these bacteria are supplemented with histidine in their growth media, they cease intracellular histidine synthesis. Propose three distinct regulatory mechanisms to account for why histidine production ends when histidine is present in the growth medium. To further investigate this phenomena, you analyse the quantity of intracellular histidine synthetase protein produced when cells are cultured with and without histidine. The quantity of this protein is same in both scenarios. Which regulatory mechanism makes sense in light of this observation?Describe a common feature at the active site of serine proteases and acetyl cholinesterase
- 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.serine proteases act via a two-step catalytic mechanism. However, as a critical scientist, you may want to see data that supports this claim. One experiment that can provide such evidence is called a 'pre-steady state' kinetics experiment using the chromogenic substrate, N-acetyl- phenylalanine p-nitrophenyl ester. As shown below when this substrate is cleaved, the p-nitrophenylate is a yellow product whose absorbance can be measured in real time using a spectrophotometer. When the chromogenic substrate is rapidly mixed together with a limiting amount of protease enzyme, the accumulation of product is measured right away on fast (millisecond) timescales. In this experiment, one observes two distinct phases of the reaction as shown in the plot below. Based upon what you know about the mechanism of serine proteases, provide a mechanistic interpretation for the observation of these two phases of the reaction. + H₂O N-Acetyl-L-phenylalanine p-nitrophenyl ester p-Nitrophenolate Absorbance…a) Based on the mechanism shown in Figure 2A, what type of enzyme is transpeptidase? : Lyase Isomerase Ligase Hydrolase Oxidoreductase Transferase b) Transpeptidases have two substrates. From Figure 2A, what type of mechanism do they most likely adopt in processing the two substrates? sequential or ping-pong c) β-lactams inactivate transpeptidases by forming a covalent bond with the serine residue in the active site. Based on this description and Figure 2B caption, what type of inhibitor are β-lactams? _________________________________________ d) Based on the mechanism for lactamase shown in Figure 3, what type of enzyme is lactamase? Lyase Isomerase Ligase Hydrolase Oxidoreductase Transferase e) Based on your answer in d, what other reactant, in addition to the antibiotic substrate, needs to be in the active site of lactamase for the hydrolysis reaction to proceed? ____________________
- Give a possible set of bacterial factors (or lack thereof) and what properties they have that would explain an increase in the 50% inhibitory concentration for tetracycline by 1,000-fold in an organism.Using the catalytic mechanism of serine proteases, draw and label a reaction coordinate diagram/graph of the chymotrypsin-catalyzed hydrolysis of a peptide bond.Mucins found on adenocarcinoma cells carry O-glycans terminated with sialic acids (such as the Sialyl Tn antigen) that are smaller and less branched than O-glycans found in healthy epithelial cells. Based on what you know about the biosynthetic pathway for O-glycans, explain this observation.
- You have isolated a new protease that cleaves peptide bonds on the carboxyl side of Asp and Glu. Based on the enzyme's inactivation by DIPF, you suspect that it may utilize a mechanism similar to chymotrypsin. The difference in specificity might be explained by the absence of the S1 binding pocket. replacement of serine 195 with a positively charged residue. presence of a positively charged residue in the S1 binding pocket. presence of a negatively charged residue in the S1 binding pocket.Describe which enzymes are required for lactose and tryptophan metabolism in bacteria when lactose and tryptophan, respectively, are (a) present and (b) absent.A bacterial lactose transporter, which is highly specific for lactose, contains a Cys residue that is essential to its transport activity. Covalent reaction of N-ethylmaleimide (NEM) with this Cys residue irreversibly inactivates the transporter. A high concentration of lactose in the medium prevents inactivation by NEM, presumably by sterically protecting the Cys residue, which is in or near the lactose-binding site. You know nothing else about the transporter protein. Suggest an experiment that might allow you to determine the Mr of this Cys-containing transporter polypeptide.