Answer b and c 1. Requirements of Active Sites in EnzymesThe active site of an enzyme usually consists of a pocket on the enzyme surface lined with aminoacid side chains necessary to bind the substrate and catalyze its chemical transformation.Carboxypeptidase, which sequentially removes the carboxyl-terminal amino acid residues fromits peptide substrates, consists of a síngle chain of 307 amino acids. The two essential catalyticgroups in the active site are furnished by Arg45 and Glu²7º.(a) If the carboxpeptidase chain were a perfect a-helix, how far apart (in nanometers)would Arg'45 and Glu²7º be? Hint: In an æ-helix, there is 1.5 Å translation of the backbone perresidue (Chapter 3).(b) Explain how it is that these two amino acids, so distantly separated in the sequence,can catalyze a reaction occurring in the space of a few tenths of a nanometer.(c) If only these two catalytic groups are involved in the mechanism of hydrolysis, whyis it necessary for the enzyme to contain such a large number of amino acid residues?270

Peptidases are enzymes that cleave peptide bonds and peptides. Carboxypeptidases are peptidases…

1. Requirements of Active Sites in Enzymes The active site of an enzyme usually consists of a pocket on the enzyme surface lined with amino acid side chains necessary to bind the substrate and catalyze its chemical transformation. Carboxypeptidase, which sequentially removes the carboxyl-terminal amino acid residues from its peptide substrates, consists of a síngle chain of 307 amino acids. The two essential catalytic groups in the active site are furnished by Arg145 and Glu²7º. (a) If the carboxpeptidase chain were a perfect a-helix, how far apart (in nanometers) would Arg45 and Glu²7º be? Hint: In an æ-helix, there is 1.5 Å translation of the backbone per residue (Chapter 3). (b) Explain how it is that these two amino acids, so distantly separated in the sequence, can catalyze a reaction occurring in the space of a few tenths of a nanometer. ,270

1. Requirements of Active Sites in Enzymes The active site of an enzyme usually consists of a pocket on the enzyme surface lined with amino acid side chains necessary to bind the substrate and catalyze its chemical transformation. Carboxypeptidase, which sequentially removes the carboxyl-terminal amino acid residues from its peptide substrates, consists of a síngle chain of 307 amino acids. The two essential catalytic groups in the active site are furnished by Arg145 and Glu²7º. (a) If the carboxpeptidase chain were a perfect a-helix, how far apart (in nanometers) would Arg45 and Glu²7º be? Hint: In an æ-helix, there is 1.5 Å translation of the backbone per residue (Chapter 3). (b) Explain how it is that these two amino acids, so distantly separated in the sequence, can catalyze a reaction occurring in the space of a few tenths of a nanometer. ,270

Biology: The Dynamic Science (MindTap Course List)

4th Edition

ISBN:9781305389892

Author:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Publisher:Peter J. Russell, Paul E. Hertz, Beverly McMillan

Chapter6: Energy, Enzymes, And Biological Reactions

Section: Chapter Questions

Problem 8TYK: Which of the following statements about the allosteric site is true? a. The allosteric site is a...

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Which of the following statements about the allosteric site is true? a. The allosteric site is a second active site on a substrate in a metabolic pathway. b. The allosteric site on an enzyme can allow the product of a metabolic pathway to inhibit that enzyme and stop the pathway. c. When the allosteric site of an enzyme is occupied, the reaction is irreversible and the enzyme cannot react again. d. An allosteric activator prevents binding at the active site. e. An enzyme that possesses allosteric sites does not possess an active site.
Which of the following statements about inhibition is true? a. Allosteric inhibitors and allosteric activators are competitive for a given enzyme. b. If an inhibitor binds the active site, it is considered noncompetitive. c. If an inhibitor binds to a site other than the active site, this competitive inhibition. d. A noncompetitive inhibitor is believed to change the shape of the enzyme, making its active site inoperable. e. Competitive inhibition is usually not reversible.
nzymes play a fundamental role in cell function. Regarding the biochemistry of enzymes, which of the following statements is correct? A. Most enzymes can bind and react with a wide range of different substrate molecules. B. Enzymes increase the rate of a spontaneous reaction by lowering the ΔG. C. Enzymes increase the enthalpy (H) of the products compared to the reactants. D. Enzymes increase the number of molecules that get to the transition state.
An enzyme contains an active site aspartic acid with a pKa = 5.0, whichacts as a general acid catalyst. On the accompanying template, draw thecurve of enzyme activity (reaction rate) versus pH for the enzyme (assumethat the protein is stably folded between pH 2–12 and that the active siteAsp is the only ionizable residue involved in catalysis). Briefly explain theshape of your curve.
1. Substrates and reactive groups in an enzyme’s active site must be precisely aligned in order for a productive reaction to occur. Why, then, is some conformational flexibility also a requirement for catalysis? 2. Some plants contain compounds that inhibit serine proteases. It has been hypothesized that these compounds protect the plant from proteolytic enzymes of insects and microorganisms that would damage the plant. Tofu, or bean curd, possesses these compounds. Manufacturers of tofu treat it to eliminate serine protease inhibitors. Why is this treatment necessary?
Studies at diff erent pH’s show that an enzyme has two catalytically important residues whose pKs are ∼4 and ∼10. Chemical modifi cation experiments indicate that a Glu and a Lys residue are essential for activity. Match the residues to their pKs and explain whether they are likely to act as acid or base catalysts.
8.Choose the False statement about enzyme binding sites Binding at an allosteric site ca affect binding and catalysis at the Ortho steric site. In addition to ortho steric sites , some enzymes have other sites where catalysis can be conducted. They are called , allosteric sites, from “allo,” the other. In principle, allosteric ligands can have structures that do not resemble those of substrates. Ligand binding at an allosteric site can cause a conformational change of an enzyme. Enzyme can be inhibited by an allosteric ligand that does not complete with substrate.
Enzyme X exhibits maximum activity at pH = 6.3. X shows a fairly sharp decrease in its activity when the pH goes much lower than 5.8. One likely interpretation of this pH activity is that: a Glu residue on the enzyme is involved in the reaction. a Tyr residue on the enzyme is involved in the reaction. a His residue on the enzyme is involved in the reaction the enzyme uses NADH has a cofactor. the enzyme uses coenzyme A has a cofactor.
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.
#1 Specify the role each of the following amino acids play within the crystal structure and/or active site for Be as specific as possible, with pictures (and mechanistic arrows) as necessary. His11 Arg140 Glu89 Trp68 #2 Provide a step-wise mechanism for the reaction Bisphosphoglycerate mutase catalyzes, using the amino acids responsible for aiding in catalysis. You do not need to add surrounding amino acids that aid in substrate specificity. (drawn out)
A histidine was determined to be the critical residue involved in an enzyme-catalyzed reaction. If the pKa of the histidine is known to be 6.5 in the active site and the pH of maximum catalytic activity is 7.2, what is likely the primary role of histidine in the catalytic reaction? A. forms a covalent bond with the substrate B. reduces the entropy of the substrate C. stabilizes a charged intermediate D. acts as a proton donor Aspartate and lysine are in the active site of an enzyme. They are both known to participate directly in catalysis. The pKa's of the residues are found to be 3.2 and 9.6, respectively for aspartate and lysine. The optimum pH for the enzyme is 6.4. Which forms of these two residues will predominate when the enzyme is most active? A. aspartate is protonated; lysine is deprotonated B. both residues are deprotonated C. aspartate is deprotonated; lysine is protonated D. both residues are protonated
1. Consider the three-dimensional model of the tertiary structure of an enzyme below. Amino acids involved in binding are shaded blue, and amino acids involved in catalysis are shaded red. A. Suppose research has shown that amino acid 82 in the red shaded region is lysine, an amino acid with a positively-charged side chain. This lysine is critical for catalysis. Other studies have found that amino acids 12 and 62 in the blue region are both phenylalanine, an amino acid with a nonpolar side chain, and are critical for substrate binding. These amino acids are relatively close in the active site but are separated by 20-70 amino acids in the primary structure. Using what you know about protein structure, explain how amino acids separated in the primary structure can come close together in the active site. B. Use this information and figure 4.2 in your book to answer the following questions: Do you think changing amino acid 82, lysine, an amino acid with a positively-charged side…