Chem 464 Biochemistry - Test 2. All Answers Verified

Which of the following statements about protein-ligand binding is correct? A) The Kass is equal to the concentration of ligand when all of the binding sites are occupied. B) The Kass is independent of such conditions as salt concentration and pH. C) The larger the Kass (association constant), the weaker the affinity. D) The larger the Kass, the faster is the binding. E) The larger the Kass, the smaller the Kdis (dissociation constant). 2. Enzymes differ from other catalysts in that only enzymes: A) are not consumed in the reaction. B) display specificity toward a single reactant. C) fail to influence the equilibrium point of the reaction. D) form an activated complex with the reactants. E) lower the activation energy of the reaction catalyzed. 3. In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the: A) curvature of the plot. B) intercept on the l/[S] axis. C) intercept on the l/V axis. D) pK of the plot. E) Vmax. 4. Both water and glucose share an -OH that can serve as a substrate for a reaction with the terminal phosphate of ATP catalyzed by hexokinase. Glucose, however, is about a million times more reactive as a substrate than water. The best explanation is that: A) glucose has more -OH groups per molecule than does water. B) the larger glucose binds better to the enzyme; it induces a conformational change in hexokinase that brings active-site amino acids into position for catalysis. C) the -OH group of water is attached to an inhibitory H atom, while the glucose -OH group is attached to C. D) water and the second substrate, ATP, compete for the active site resulting in a competitive inhibition of the enzyme. E) water normally will not reach the active site because it is hydrophobic. 5. Allosteric enzymes: A) are regulated primarily by covalent modification. B) usually catalyze several different reactions within a metabolic pathway. C) usually have more than one polypeptide chain. D) usually have only one active site. E) usually show strict Michaelis-Menten kinetics.2 6. Which of the following monosaccharides is not a carboxylic acid? A) 6-phospho-gluconate B) gluconate C) glucose D) glucuronate E) muramic acid 7. The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine is: A) a deoxyribonucleoside. B) a purine nucleotide. C) a pyrimidine nucleotide. D) adenosine monophosphate. E) adenosine. Answer any 7 of the following 8 questions. If you answer ll 8 questions I will throw out the question with the lowest score. 8. First compare and contrast the oxygen binding curves of myoglobin and hemoglobin. Next compare and contrast the structures of myoglobin and hemoglobin. Finally use the difference between the structures to explain the different binding curves. Define the following terms: apoenzyme uncompetitive inhibitor protein phosphatase specificity constant transition state analog Below is the mechanism for an enzyme. Pick out the various types of catalysis discussed in class that you can see in this mechanism: In the first step the His is acting as a general base, and the serine is acting both as a general acid as it donates it proton to the his, and as a general base as it donates it electrons to the substrate. At this point a covalent bond is formed between the substrate and the enzyme so you have covalent catalyst. Next the His acts as a general acid by donating its H to the substrate, and half of the substrate molecules is released from the enzyme. 4. Below is a plot of V0 (Y- Mol/sec) of an enzymatic reaction plotted against the substrate concentration (X- Molarity) The Vmax of the enzyme The KM of the enzyme If the enzyme concentration is 50 ìM, what is the kcat of the enzyme? What is the specificity constant for this enzyme? What is a reducing sugar and why is it important? How does a sugar get to be a ‘nonreducing’ sugar. Please name at least 1 non-reducing sugar How is a glycoprotein different than a proteoglycan? How are they the same? You have always heard about DNA carrying the genetic information from generation to generation in a cell, yet in the chapter on carbohydrates I also talked about carbohydrates carrying information. What kinds of information do carbohydrates carry and why can carbohydrates carry more information per unit of monomer than DNA can? 8. Eureka, a spacecraft on the planet Zeffess has discovered life. The structure of their nucleic acids are a lot like ours, the only difference is that instead of a ribose sugar the bases are attached to glucose in at the 1' carbon in an â linkage. A second difference is that the glucose in the Zeffuss nucleic acid is a 3' deoxy derivative. Draw the structure of cytosine in a 1'â linkage to 3' deoxyglucose