Life: The Science of Biology
11th Edition
ISBN: 9781319010164
Author: David E. Sadava, David M. Hillis, H. Craig Heller, Sally D. Hacker
Publisher: W. H. Freeman
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Chapter 8.5, Problem 2R
Summary Introduction
To review:
The observation in an increase of active enzyme molecules than inactive forms when a competitive inhibitor is added to a solution containing the enzyme, which is under allosteric regulation.
Introduction:
Enzymes are allosterically regulated by the conjunction of effector molecules on sites other than the active site. These effector molecules can either regulate enzyme activity positively or negatively. Competitive inhibitors, on the other hand, compete with the substrates to bind to the active site and thus prevent the formation of products.
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Define enzyme inhibition. Explain in detail the different types of inhibitions with
suitable examples.
Under the following conditions, fill in the blanks. Then, describe why this inhibitor is the type of inhibitor you identified it as.
If you were to add 5nM of a reversible inhibitor, the Km for the measured enzyme catalyzed reaction would ______ (Increase, Decrease, Stay the same) to ______µM (choose appropriate value) and Vmax would _______ (Increase, Decrease, Stay the same) to ______µMs-1. So, this inhibitor is a ______ (Competitive, Uncompetitive, Mixed) inhibitor.
Conditions:
kcat = 130 s^-1
Vo = 3.0 μMs-1
S = 10 μM
Et = 0.09 µM
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.
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Life: The Science of Biology
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- Would you expect the structure of a noncompetitive inhibitor of a given enzyme to be similar to that of its substrate?arrow_forwardDescribe the two models that explain the behavior of allosteric enzymes. Include thelimitation or advantage of each. Give also an example of each.arrow_forwardb) Enzymes accelerate reactions by facilitating the formation of the transition state. Define transition state and activation energy. For full credit, you need to present the actual graph (for an endergonic or exergonic reaction - make sure to specify your choice) highlighting each term? c) Explain how an irreversible inhibitor for an enzymatic reaction differs from reversible inhibitors. Provide specific example of an irreversible inhibitor and its target enzyme d) Determine the Vo as a function of Vmax when the substrate concentration is equal to 10 KM or 20 KM. What does this tell you about an enzyme ability to reach Vmax?arrow_forward
- A generalized enzyme active site is shaped like a hemisphere with a radius of 45Å. The active site holds the following amino acids in a homeostatic solution (pH = 7.38): -HAVARILKHAVARILKHAVARILK- Assuming the charge is distributed uniformly along the hemisphere, determine the force at which this active site acts upon a single ATP molecule at the center of the hemisphere.arrow_forwardFor a lot of enzymes that work on fatty acids, the rate determining step is the release of the product from the active site. This means that the activation energy for product release is much higher than the free energy of catalysis. What enthalpic or entropic contributions would make the activation energy for product release so high and explain?arrow_forwardWhen 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 substratesarrow_forward
- An enzyme catalyzes the following reaction. Which of the following inhibitors would you expect to be competitive inhibitors and which non-competitive inhibitors? Please explain briefly.arrow_forwardIdentify 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.arrow_forwardA 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…arrow_forward
- An enzymes catalyzed reaction is studied in the presence and absence of an inhibitor. The following data was obtained in the image provided. Plot 1/[S] as abscissa and 1/V as ordinate for both catalyzed reactions and reaction with inhibitor. Use the same graph for both plots Calculate the following: Km of enzyme in the reaction without inhibitor Km' of the enzyme in the reation with inhibitor Vmax of the uninhibited reaction Vmax of the inhibited reaction What kind of inhibitor was added to the enzyme catalyzed reaction? Explain your answer in terms of changes in Km and Vmax.arrow_forwardWhen 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.arrow_forwardExplain how the following changes affect the rate of an enzyme-catalyzed reaction in the presence of an uncompetitive inhibitor: (a) increasing the substrate concentration at a constant inhibitor concentration, (b) decreasing the inhibitor concentration at a constant substrate concentration.arrow_forward
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