Old Dominion UniversityCHEM 441EXAM 2 BIOCHEMISTRY ( with all answers 100% CORRECT )

Question 1 0 out of 2 points Questions #1-3. A certain protein can bind one of two ligands: ligand A or ligand B. Below is a plot of the fractional saturation (Y) versus [ligand] for ligand A and l igand B. Question #1: By simply inspecting the graph, what is an approximate Kd(dissociation constant) for ligand A? Indicate appropriate units; briefly explain how you arrived at your answer. Selected Answer: Kd= [P][L] / [PL] = [50][60]/[50x60] =1 Correct Answer: ~ 50 uM (the Kd is the [ligand] at which half-saturation occurs) -- for ligand A, when Y = 50% (y-axis), that corresponds to a [ligand A] of somewhere between 40 & 60 uM on the x-axis. Response Feedback: [None Given] Question 2 0 out of 2 points Question #2: By simply inspecting the graph, what is an approximate Kd(dissociation constant) for ligand B? Indicate appropriate units; briefly explain how you arrived at your answer. Selected Answer: Kd= [P][L] / [PL] =[50][260]/[50x260] =1 Correct Answer: ~ 200 uM (the Kd is the [ligand] at which half-saturation occurs) -- for ligand B, when Y = 50% (y-axis), that corresponds to a [ligand B] of somewhere right around 200 uM on the x-axis. Response Feedback: [None Given]  Question 3 2 out of 2 points Question #3: Which ligand, A or B, binds to the protein with higher affinity? Briefly explain your answer. Selected Answer: I think that Lingand A have the affinity to bind with a protein as it has a great intermolecular force between the lingands and the receptors. Correct Answer: Ligand A has a higher affinity because it has a lower Kd, i.e., 50% saturation (half the sites occupied) occurs at a lower concentration for ligand A. Response Feedback: [None Given]  Question 4 1 out of 1 points Myoglobin (choose any/all answers that apply): Selected Answers: B. is comprised of eight alpha-helices. Answers: A. is a multimeric protein. B. is comprised of eight alpha-helices. C. binds 2,3-bisphosphoglycerate at its heme group. D. cooperatively binds oxygen. E. transports oxygen in the blood.  Question 5 3 out of 3 pointsHemoglobin (choose any/all answers that apply): Selected Answers: B. is a multimeric protein. C. transports oxygen in the blood. D. cooperatively binds oxygen. E. binds 2,3-bisphosphoglycerate at its heme group. Answers: A. is primarily comprised of beta-sheets. B. is a multimeric protein. C. transports oxygen in the blood. D. cooperatively binds oxygen. E. binds 2,3-bisphosphoglycerate at its heme group.  Question 6 1 out of 1 points The amino acid substitution of Valine for Glutamate in Hemoglobin S (sickle cell Hb) results in aggregation of the protein due to ____________ interactions between molecules. Selected Answer: E. hydrophobic Answers: A. covalent B. ionic C. hydrogen bonding D. disulfide E. hydrophobic  Question 7 0 out of 1 pointsThe Lehninger text briefly describes the catalytic mechanism of enolase (see p. 220); this image comes from Figure 6-26: Question: The reaction mechanism for enolase is most accurately described as: Selected Answer: C. bi-uni Answers: A. uniuni B. uni-bi C. bi-uni D. bi-bi  Question 8 3 out of 3 points In what type of catalysis does Lys345 engage during the very first step of enolase's reaction cycle (see Question #7)? Explain, in your own words, specifically why and how Lys345 falls into the category you chose. Selected Answer: The type of catalysis reaction that Lys345 engages during the very first step of enolase's reaction cycle is hydro-lyases because Lys345 removes a proton by general base catalysis. Correct Answer: Lys345 engages in general base catalysis during the first reaction step (Step #1 in Figure 6-23a). This is because the Lys345 side chain acts initially as a proton acceptor (i.e. it acts as a base), stealing away the hydrogen ion off of the central carbon within the 2-phosphoglycerate substrate. Response [None Given]Feedback:  Question 9 1 out of 1 points In the enolase reaction mechanism (see Question #7), the magnesium ions are directly engaged in a type of: Selected Answer: D. electrostatic catalysis. Answers: A. acid catalysis. B. base catalysis. C. covalent catalysis. D. electrostatic catalysis. E. repellant catalysis.  Question 10 1 out of 1 points This information pertains to Questions #10-15. The following observations come from Lineweaver-Burke plots, based on kinetic data generated from a Michaelis/Menton-type enzyme (E) that catalyzes the hydrolysis of a peptide substrate (S). All data were generated in the presence of 18.0 μM total enzyme. The enzyme-catalyzed reaction has a Km of 3.00 μM and a Vmax of 2.00 μM/sec. The enzyme-catalyzed reaction in the presence of 15.0 μM of Inhibitor A has an apparent Km of 2.25 μM and an apparent Vmaxof 1.50 μM/sec. The enzyme-catalyzed reaction in the presence of 15.0 μM of Inhibitor B has an apparent Km of 3.80 μM and an apparent Vmaxof 2.00 μM/sec. Question #10: Inhibitor B is a(n): Selected Answer: A. competitive inhibitor. Answers: A. competitive inhibitor. B. uncompetitive