EBK LIFE: THE SCIENCE OF BIOLOGY
11th Edition
ISBN: 8220103935432
Author: Sadava
Publisher: MAC HIGHER
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Chapter 8, Problem 5Q
Summary Introduction
To review:
The property of an enzyme in general, which enables luciferase to attach only to luciferin molecule. Also, explain catalysis by luciferase taking this enzymatic property into consideration.
Introduction:
The fireflies show the phenomenon of bioluminescence with the help of luciferin, which is present in their abdomen in an organ known as a lantern. This reaction takes place in the presence of an enzyme luciferase, which behaves as a catalyst.
The enzyme luciferase undergoes a change in the shape when it binds to luciferin and adenosine triphosphate (ATP). This prevents the attachment of the water molecule at the active site of the enzyme.
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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.
For 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?
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.
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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.
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Chapter 8 Solutions
EBK LIFE: THE SCIENCE OF BIOLOGY
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- 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.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_forwardConsider the following mechanism: What kind of reaction is occurring during this step of glycolysis? What metabolite is in Box 1? What metabolite is in Box 2? What metabolite is in Box 3? What enzyme catalyzes this reaction? Circle and label one place on the mechanism where covalent catalysis is occurring. Suggest an amino acid that could fill the role of residue “A” in the mechanism above and draw its structure at pH 7.4. Suggest an amino acid that could fill the role of residue “B” in the mechanism above and draw its structure at pH 7.4. Under standard conditions, this reaction is unfavorable (DG¢° = 23.8 kJ/mol). What conditions in the cell allow for the actual free energy change to be lower (DG » 0), making the reaction readily reversible? Explain your answer. *please help and explain as well as you can*arrow_forward
- The 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.arrow_forwardAll of the following statements about competitive and non-competitive inhibitors are true EXCEPT:(a) Competitive inhibitors are structurally similar to anenzyme’s substrate and bind to the enzyme’s allostericsite.(b) Competitive inhibitors work by competing with a sub-strate for binding to an enzyme’s active site.(c) Noncompetitive inhibitors can bind at sites other thanthe active site of an enzyme, distorting the tertiary pro-tein structure, which alters the shape of the active site,rendering it ineffective for substrate binding.(d) Some noncompetitive inhibitors bind reversibly whilesome bind irreversibly to their enzyme.(e) b and d.arrow_forwardBecause it resembles the two physiological substrates, phosphonacetyl L - aspartate (PALA) is a strong inhibitor of ATCase. Low concentrations of this unreactive bisubstrate analog, on the other hand, enhance reaction velocity in the presence of substrates. The reaction rate rises as PALA is added, until three molecules of PALA are attached per molecule of enzyme. This maximum velocity is 17 times higher than it would be without PALA. With the addition of three additional molecules of PALA per molecule of enzyme, the reaction rate drops to practically nil. Why does PALA activate ATCase at such low concentrations?arrow_forward
- Suppose that you have isolated the enzyme sucrase (able to hydrolyze sucrose into glucose and fructose), and you wish to determine the nature of inhibitor A for this enzyme. You have prepared five different concentrations of substrate (sucrose), and five different concentrations of inhibitor A (plus the control, with zero mM of inhibitor A). The following Table lists the inhibitor A concentrations [I], substrate concentrations [S], and resulting enzyme velocities (Vo) for all six of these experiments: [I] [S] Vo 1/[S] 1/ Vo 0 mM 0.1 mM 0.333333333333 mM per minute 0 mM 0.2 mM 0.50 0 mM 0.3 mM 0.60 0 mM 0.4 mM 0.666666666667 0 mM 0.5 mM 0.714285714286 0.1 mM 0.1 mM 0.20 0.1 mM 0.2 mM 0.333333333333 0.1 mM 0.3 mM 0.428571428571 0.1 mM 0.4 mM 0.50 0.1 mM 0.5 mM 0.555555555556 0.20 mM 0.1 mM 0.142857142857…arrow_forwardThe brown discoloration of apples and potatoes is due to an enzyme catalyzed chemical reaction. What is the enzyme that catalyzes this reaction? What is the substrate(s) of this reaction? What is the product(s) of this reaction? Does this reaction require a cofactor, if so which one?arrow_forwardWhich one is transition and substrate state? What must be true of a and b in order for catalysis to occur?arrow_forward
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