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Chemistry 4202 Homework 3: Enzyme Inhibition and Regulation, Assignments of Biochemistry

A chemistry homework assignment focused on enzyme inhibition and regulation. It includes multiple-choice questions about competitive, noncompetitive, and uncompetitive inhibitors, as well as questions about the structures of sulfanilamide and para-aminobenzoic acid, and the mechanism of aspirin's inhibition of cyclooxygenase-2. The assignment also includes a question about generating a lineweaver-burk plot for an enzyme-catalyzed hydrolysis reaction. Lastly, there is a question about a biosynthetic pathway and the regulation of its enzymes by their products.

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Pre 2010

Uploaded on 08/04/2009

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Chemistry 4202 Name
_________________________________
Homework 3
20 points
1. A competitive inhibitor of an enzyme:
A. increases KM without affecting Vmax.
B. decreases KM without affecting Vmax.
C. increases Vmax without affecting KM.
D. decreases both KM and Vmax.
2. The presence of a noncompetitive inhibitor:
A. leads to both an increase in the Vmax of a reaction and an increase in the KM.
B. leads to a decrease in the observed Vmax.
C. leads to a decrease in KM and Vmax.
D. leads to an increase in KM without affecting Vmax.
3. Sulfonamides (sulfa drugs) such as sulfanilamide are antibacterial drugs that
inhibit the enzyme dihydropteroate synthase (DS) that is required for the
synthesis of folic acid in bacteria.
(a) Draw the structure of sulfanilamide.
(b) Draw the structure of para-aminobenzoic acid (PABA).
(c) If PABA is a substrate for DS, what type of inhibition can be predicted for the
bacterial synthase enzyme in the presence of sulfonamides?
4. On the same graph, plot 1/v0 versus 1/[S] for a typical enzyme reaction (a) in the
absence of an inhibitor, (b) in the presence of a competitive inhibitor, (c) in the
presence of an uncompetitive inhibitor, and (d) in the presence of a
noncompetitive inhibitor.
5. The therapeutic anti-inflammatory effects of aspirin arise from its inhibition of the
enzyme cyclooxygenase-2 (Cox-2, also known as PGH2 synthase), which is involved in
the synthesis of prostaglandins, mediators of inflammation, pain, and fever. Research
the mechanism of inhibition and answer the following questions.
(a) Briefly explain the mechanism of inhibition. What type of inhibition is it?
(b) Aspirin can also inhibit a related intestinal enzyme cyclooxygenase-1 (Cox-1).
What side effects can result from the inhibition of this enzyme? Why?
6. Consider the following data for an enzyme-catalyzed hydrolysis reaction in the
absence and presence of an inhibitor I:
[Substrate] (mM) v0 (mM/min) v0 with I present
(mM/min)
0.5 0.81 0.42
0.67 0.95 0.53
1.0 1.25 0.71
2.0 1.61 1.08
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Chemistry 4202 Name


Homework 3 20 points

  1. A competitive inhibitor of an enzyme: A. increases KM without affecting Vmax. B. decreases KM without affecting Vmax. C. increases Vmax without affecting KM. D. decreases both KM and Vmax.
  2. The presence of a noncompetitive inhibitor: A. leads to both an increase in the Vmax of a reaction and an increase in the KM. B. leads to a decrease in the observed Vmax. C. leads to a decrease in KM and Vmax. D. leads to an increase in KM without affecting Vmax.
  3. Sulfonamides (sulfa drugs) such as sulfanilamide are antibacterial drugs that inhibit the enzyme dihydropteroate synthase (DS) that is required for the synthesis of folic acid in bacteria. (a) Draw the structure of sulfanilamide. (b) Draw the structure of para -aminobenzoic acid (PABA). (c) If PABA is a substrate for DS, what type of inhibition can be predicted for the bacterial synthase enzyme in the presence of sulfonamides?
  4. On the same graph, plot 1/ v 0 versus 1/[S] for a typical enzyme reaction (a) in the absence of an inhibitor, (b) in the presence of a competitive inhibitor, (c) in the presence of an uncompetitive inhibitor, and (d) in the presence of a noncompetitive inhibitor.

5. The therapeutic anti-inflammatory effects of aspirin arise from its inhibition of the

enzyme cyclooxygenase-2 (Cox-2, also known as PGH 2 synthase), which is involved in the synthesis of prostaglandins, mediators of inflammation, pain, and fever. Research the mechanism of inhibition and answer the following questions. (a) Briefly explain the mechanism of inhibition. What type of inhibition is it? (b) Aspirin can also inhibit a related intestinal enzyme cyclooxygenase-1 (Cox-1). What side effects can result from the inhibition of this enzyme? Why?

  1. Consider the following data for an enzyme-catalyzed hydrolysis reaction in the absence and presence of an inhibitor I : [Substrate] (mM) v 0 (mM/min) v 0 with I present (mM/min) 0.5 0.81 0. 0.67 0.95 0. 1.0 1.25 0. 2.0 1.61 1.

Chemistry 4202 Name


Homework 3 20 points (a) Generate a Lineweaver-Burk plot for the data. (b) What type in inhibition is being measured?

  1. A biosynthetic pathway proceeds from compound A to compound E in four steps and then branches. One branch is a two-step pathway to G, and the other is a three-step pathway to J. Substrate A is a feed-forward activator of the enzyme that catalyzes the synthesis of E. Products G and J are feedback inhibitors of the initial enzyme in the common pathway, and they also inhibit the first enzyme after the branch point in their own pathways. (a) Draw a diagram showing the regulation of this metabolic pathway. (b) Why is it advantageous for each of the two products to inhibit two enzymes in the pathway?