MT3 2009

MT3 2009 - Name _ Midterm Exam 3 Chem114A (Instructor:...

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Name _______________________________ 1 Midterm Exam 3 Chem114A (Instructor: Hector Viadiu) Fall 2009 (December 2, 2009) 1. In the following graph, label which binding curves correspond to: myoglobin, hemoglobin and a hypothetical non-cooperative hemoglobin (3 points). Explain the different behavior of myoglobin and hemoglobin at 20 and 100 torrs (4 points). Mention three differences between the T and R states of hemoglobin (3 points). Green: Myoglobin (1 point) Red: Hemoglobin (1 point) Blue: Hypothetical protein (1 point) At 100 torrs, both proteins have high affinity for oxygen (1 point). At 20 torrs, myoglobin continues having high affinity for oxygen (7% lower than the maximum) (1 point), while hemoglobin affinity drops (66% of the maximum) (1 point). Percentages not needed. T state: It is the tense deoxy form of the tetrameric protein because it has constrained subunit-subunit interactions (2 points). R state: It is the relaxed oxygenated form of the tetrameric protein because it has less constrained subunit-subunit interactions. The oxygen binding sites are free of strain and are capable of binding oxygen with higher affinity than are the sites in the T state (2 points).
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Name _______________________________ 2 2. Explain how the depicted experiment was performed (3 points) and trace the substrate concentration versus initial velocity plot that results from such data and fits the Michaelis-Menten equation V o =V max ([S]/[S]+ K M ) (3 points). Using the graph that you just drew explain the meaning of Vmax and K M (4 points). This experiment was performed by measuring the rate of appearance of the product at different substrate concentrations (3 points). Each substrate concentration will give an initial velocity value that is used to plot the following: If the graph is drawn (3 points). Vmax is the maximum velocity of an enzymatic reaction when the binding site is saturated with substrate (2 points). Km is the substrate concentration at which the reaction rate is half of Vmax (2 points).
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Name _______________________________ 3 3. Do enzymes modify the equilibrium of a reaction? NO (1 point). The following schemes and double reciprocal graphs represent the three different types of reversible inhibitors. Mention each type (3 points) and describe the effects that each of them has on an enzyme’s V max and K M (6 points). Competitive Uncompetitive Noncompetitive Vmax remains the same Vmax is reduced Vmax is reduced Km increases Km is reduced Km remains the same
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Name _______________________________ 4 4. Catalytic mechanism of chymotrypsin. Name the amino acids that form the catalytic triad of chymotrypsin (1 point), circle the tetrahedral intermediates (1 points), the acyl-
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This note was uploaded on 03/06/2011 for the course CHEM 120A taught by Professor Figueroa during the Spring '10 term at UCSD.

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MT3 2009 - Name _ Midterm Exam 3 Chem114A (Instructor:...

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