In bacteria, isocitrate dehydrogenase is regulated by phosphorylation of a specific Ser residue in the enzyme active site. X-ray structures of the phosphorylated and the nonphosphorylated enzyme show no significant conformational differences. How does phosphorylation regulate isocitrate dehydrogenase activity? O The phosphoryl group sterically hinders the substrate. O The phosphorylation bears a negative charge, which repels the substrate. O The phosphoryl group attracts positively charged Ca2* cations, which block the active site on the enzyme. None of the above.
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- When enzyme solutions are heated, there is a progessive loss of catalytic activty over time due to denaturation of the enzyme. A solution of the enzyme hexokinase incubated at 45 degrees Celsius lost 50% of its activity in 12 minutes, but when incubated at 45 degrees Celsius in the presence of a very large concentration of one of its substrates, it lost only 3% of its activity in 12 minutes. Suggest why thermal denaturation of hexokinase was retarded in the presence of one substrates.An enzyme that catalyzes a reaction such as the one below is alan: || C-0 || C-0 C=0 С —о — Н I| Н-С—Н H- C H H isomerase O kinase O dehydratase O dehydrogenase O phosphorylase O - IIdentify the type of regulation of enzyme activity seen in the following situations - for example, competitive inhibition, allosterism, phosphorylation, zymogen conversion, association-dissociation, feedback inhibition, etc. a. Trypinsogen, which is not catalytically active, is converted to the active enzyme trypsin by removal of a hexapeptide from the N-terminal end. b. The dimer protein kinases is catalytically inactive. Binding of cAMP causes protein kinase dimer to split into its monomer which are active catalysts.
- When enzyme solutions are heated, there is a progressive loss of catalytic activity over time due to denaturation of the enzyme. A solution of the enzyme hexokinase incubated at 450C lost 50% of its activity in 12 minutes, but when incubated at 450C in the presence of a very large concentration of one of its substrates, it lost only 3% of its activity in 12 minutes. Suggest why thermal denaturation of hexokinase was retarded in the presence of one substratesThe following diagram shows reaction curves for aspartate transcarbamoylase (ATCase) with carbamoylphosphate and different concentrations of aspartate, in the absence of ATP (curve 1) and presence of ATP (curve 2). What do the shapes of the curves tell us about the ATCase enzyme? 2 جر [aspartate] It binds substrate through a sequential mechanism. It binds substte cooperatively. It obeys Michaelis-Menten kinetics. It binds substrate through a concerted mechanism.When enzyme solutions are heated, there is a progressive loss of catalytic activity over time due to denaturation of the enzyme. A solution of the enzyme hexokinase incubated at 45 °C lost 50% of its activity in 12 min, but when incubated at 45 °C in the presence of a very large concentration of one of its substrates, it lost only 3% of its activity in 12 min. Suggest why thermal denaturation of hexokinase was retarded in the presence of one of its substrates.
- What are the effects of different light colors in photosynthesis? Different light colors will change the rate of photosynthesis Light color does not affect photosynthesis Carbohydrates are metabolized by light Photosynthesis does not require lightA multi-enzyme complex Is made up of three polypeptide chains, A, B and C. A is associated with decarboxylase activity; B is a transacetylase, while C is a dehydrogenase. When the protein was placed in a nonpolar solvent, then run in PAGE, two protein bands were observed. Enzyme assays showed that one protein band exhibited decarboxylase activity while the other has both transacetylase and dehydrogenase activities. When the protein was also placed in an aqueous solvent at pH 5.0, then run in electrophoresis, two protein bands were also detected. Further enzyme assays also showed that one protein band exhibits transacetytase activity while the other has both decarboxylase and dehydrogenase activities. a. What types of non-covalent interactions are possible between A, B and C? b. Addition of urea, a reducing agent gave 4 bands in the PAGE profile with a subsequent loss of decarboxylase activity. What could be the reason for the observed result? Explain briefly in terms of the structure…During chymotrypsin-mediated catalysis, which of the following statements is true? Select any/all answers that apply. O A. A basic (positively-charged) side chain of the substrate polypeptide sits within the oxyanion hole of the enzyme. O B. A basic (positively-charged) side chain of the substrate polypeptide sits within the specificity pocket of the enzyme. O C. Ser195 hydrogen-bonds with the backbone carbonyl group of the substrate polypeptide within the oxyanion hole of the enzyme. O D. All three residues that comprise the catalytic triad of the enzyme interact directly with the substrate polypeptide chain. O E. Both covalent catalysis and acid-base catalysis occur.
- If the substrate for an enzyme catalyzed reaction contained a negative charge, which of the following amino acids would most likely be present in the active site to provide electrostatic destabilization of the ES complex? Leu Val O Asp O LYS QUESTION 15 What is the function of the histidine in the diagram of the mechanism at right with the substrate, a phenylalanine residue? (n) His Asp Nucleophilic affack by water stabilization of a metal ion covalent catalysis electrostatic attraction of the substrate O acid base catalysis 789 Mustly cloudy Click Save and Submit to save and submit. Click Save All Ansuwers to save all answers. here to searchSuppose you have 100 molecules of an enzyme (an aspartyl protease) that requires aspartate in the active site for catalysis. If the pka of Asp side chain is 4.5 and you did your experiment in the presence of the proper substrate concentration and environment and at pH 4.5. Then: O a. Repeating the experiment at pH 7.5 results in achieving Vmax O b. Vmax is decreased O c. All enzyme molecules will be active O d. Vmax can be achieved O e. Repeating the experiment at pH 1.5 results in achieving VmaxWhich of the following statements are true about enzyme regulation via noncovalent interactions? Select all that apply. Molecules can cause a change in enzyme shape because they're able to bind to the enzyme somewhere other than the active site The function of an enzyme is altered by a chemical change in its primary structure, which is called phosphorylation Molecules that are similar to the substrate in both size and shape can compete with the substrate for access to the enzyme's active site Molecules that are similar to the substrate in both size and shape can compete with the substrate for access to a location other than the active site