Biochemistry 1 - Exam 2 Questions | BCH 3033, Exams of Biochemistry

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BCH 3033 name : Exam 2 (Part 1): 11.04. (1) Les questions multiples de choix de biochimie: (35 points)

1. A prosthetic group of a protein is a non-protein structure that is: A) a ligand of the protein. B) a part of the secondary structure of the protein. C) a substrate of the protein. D) permanently associated with the protein. E) transiently bound to the protein. 2. When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are occupied by: A) one O atom and one amino acid atom. B) one O 2 molecule and one amino acid atom. C) one O 2 molecule and one heme atom. D) two O atoms. E) two O 2 molecules. 3. In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as: A) hyperbolic. B) linear with a negative slope. C) linear with a positive slope. D) random. E) sigmoidal. 4. Which of the following statements about protein-ligand binding is correct? A) The K a is equal to the concentration of ligand when all of the binding sites are occupied. B) The K a is independent of such conditions as salt concentration and pH. C) The larger the K a (association constant), the weaker the affinity. D) The larger the K a, the faster is the binding. E) The larger the K a, the smaller the K d (dissociation constant). 5. Myoglobin and the subunits of hemoglobin have: A) no obvious structural relationship. B) very different primary and tertiary structures. C) very similar primary and tertiary structures. D) very similar primary structures, but different tertiary structures. E) very similar tertiary structures, but different primary structures.

6. An allosteric interaction between a ligand and a protein is one in which: A) binding of a molecule to a binding site affects binding of additional molecules to the same site. B) binding of a molecule to a binding site affects binding properties of another site on the protein. C) binding of the ligand to the protein is covalent. D) multiple molecules of the same ligand can bind to the same binding site. E) two different ligands can bind to the same binding site. 7. Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)? A) It binds at a distance from the heme groups of hemoglobin. B) It binds with lower affinity to fetal hemoglobin than to adult hemoglobin. C) It increases the affinity of hemoglobin for oxygen. D) It is an allosteric modulator. E) It is normally found associated with the hemoglobin extracted from red blood cells. 8. The fundamental cause of sickle-cell disease is a change in the structure of: A) blood. B) capillaries. C) hemoglobin. D) red cells. E) the heart. 9. An individual molecular structure within an antigen to which an individual antibody binds is as a(n): A) antigen. B) epitope. C) Fab region. D) Fc region E) MHC site. 10. The proteins of the Major Histocompatibility Complex (MHC) bind and display: A) antigen fragments. B) B cell fragments. C) immunoglobin fragments. D) macrophage fragments. E) T cell fragments. 11. Which of the following parts of the IgG molecule are not involved in binding to an antigen? A) Fab B) Fc C) Heavy chain D) Light chain E) Variable domain

12. A monoclonal antibody differs from a polyclonal antibody in that monoclonal antibodies: A) are labeled with chemicals that can be visualized. B) are produced by cells from the same organism that produced the antigen. C) are synthesized by a population of identical, or “cloned,” cells. D) are synthesized only in living organisms. E) have only a single polypeptide chain that can recognize an antigen. 13, Which of the following generalizations concerning motor proteins is correct? A) They convert chemical energy into kinetic energy. B) They convert chemical energy into potential energy. C) They convert kinetic energy into chemical energy. D) They convert kinetic energy into rotational energy. E) They convert potential energy into chemical energy. 14. One of the enzymes involved in glycolysis, aldolase, requires Zn2+^ for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it would be referred to as the: A) apoenzyme. B) coenzyme. C) holoenzyme. D) prosthetic group. E) substrate. 15. Which one of the following is not among the six internationally accepted classes of enzymes? A) Hydrolases B) Ligases C) Oxidoreductases D) Polymerases E) Transferases 16. Which one of the following statements is true of enzyme catalysts? A) Their catalytic activity is independent of pH. B) They are generally equally active on D and L isomers of a given substrate. C) They can increase the equilibrium constant for a given reaction by a thousand fold or more. D) They can increase the reaction rate for a given reaction by a thousand fold or more. E) To be effective, they must be present at the same concentration as their substrate. 17. The concept of “induced fit” refers to the fact that: A) enzyme specificity is induced by enzyme-substrate binding. B) enzyme-substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction. C) enzyme-substrate binding induces movement along the reaction coordinate to the transition state. D) substrate binding may induce a conformational change in the enzyme, which then brings

catalytic groups into proper orientation. E) when a substrate binds to an enzyme, the enzyme induces a loss of water (desolvation) from the substrate.

18. The benefit of measuring the initial rate of a reaction V 0 is that at the beginning of a reaction: A) [ES] can be measured accurately. B) changes in [S] are negligible, so [S] can be treated as a constant. C) changes in K m are negligible, so K m can be treated as a constant. D) V 0 = V max. E) varying [S] has no effect on V 0. 19. The steady state assumption, as applied to enzyme kinetics, implies: A) K m = K s. B) the enzyme is regulated. C) the ES complex is formed and broken down at equivalent rates. D) the K m is equivalent to the cellular substrate concentration. E) the maximum velocity occurs when the enzyme is saturated. 20. 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) p K of the plot. E) V max. 21. Enzyme X exhibits maximum activity at pH = 6.9. X shows a fairly sharp decrease in its activity when the pH goes much lower than 6.4. One likely interpretation of this pH activity is that: A) a Glu residue on the enzyme is involved in the reaction. B) a His residue on the enzyme is involved in the reaction. C) the enzyme has a metallic cofactor. D) the enzyme is found in gastric secretions. E) the reaction relies on specific acid-base catalysis. 22. The role of the metal ion (Mg2+) in catalysis by enolase is to A) act as a general acid catalyst B) act as a general base catalyst C) facilitate general acid catalysis D) facilitate general base catalysis E) stabilize protein conformation

23. How is trypsinogen converted to trypsin? A) A protein kinase-catalyzed phosphorylation converts trypsinogen to trypsin. B) An increase in Ca2+^ concentration promotes the conversion. C) Proteolysis of trypsinogen forms trypsin. D) Trypsinogen dimers bind an allosteric modulator, cAMP, causing dissociation into active trypsin monomers. E) Two inactive trypsinogen dimers pair to form an active trypsin tetramer. 24. A metabolic pathway proceeds according to the scheme, R  S  T  U  V  W. A regulatory enzyme, X, catalyzes the first reaction in the pathway. Which of the following is most likely correct for this pathway? A) Either metabolite U or V is likely to be a positive modulator, increasing the activity of X. B) The first product S, is probably the primary negative modulator of X, leading to feedback inhibition. C) The last product, W, is likely to be a negative modulator of X, leading to feedback inhibition. D) The last product, W, is likely to be a positive modulator, increasing the activity of X. E) The last reaction will be catalyzed by a second regulatory enzyme. 25. Which of the following monosaccharides is not an aldose? A) erythrose B) fructose C) glucose D) glyceraldehyde E) ribose 26. The reference compound for naming D and L isomers of sugars is: A) fructose. B) glucose. C) glyceraldehyde. D) ribose. E) sucrose. 27. When two carbohydrates are epimers: A) one is a pyranose, the other a furanose. B) one is an aldose, the other a ketose. C) they differ in length by one carbon. D) they differ only in the configuration around one carbon atom. E) they rotate plane-polarized light in the same direction. 28. Which of following is an anomeric pair? A) D-glucose and D-fructose B) D-glucose and L-fructose C) D-glucose and L-glucose D) -D-glucose and -D-glucose E) -D-glucose and -L-glucose

29. When the linear form of glucose cyclizes, the product is a(n): A) anhydride. B) glycoside. C) hemiacetal. D) lactone. E) oligosaccharide. 30. Which of the following is not a reducing sugar? A) Fructose B) Glucose C) Glyceraldehyde D) Ribose E) Sucrose 31. D-Glucose is called a reducing sugar because it undergoes an oxidation-reduction reaction at the anomeric carbon. One of the products of this reaction is: A) D-galactose. B) D-gluconate. C) D-glucuronate. D) D-ribose. E) muramic acid. 32. Which of the following statements about starch and glycogen is false****? A) Amylose is unbranched; amylopectin and glycogen contain many ( 1 6) branches. ) branches. B) Both are homopolymers of glucose. C) Both serve primarily as structural elements in cell walls. D) Both starch and glycogen are stored intracellularly as insoluble granules. E) Glycogen is more extensively branched than starch. 33. The basic structure of a proteoglycan consists of a core protein and a: A) glycolipid. B) glycosaminoglycan. C) lectin. D) lipopolysaccharide. E) peptidoglycan. 34. Which of the following is a dominant feature of the outer membrane of the cell wall of gram negative bacteria? A) Amylose B) Cellulose C) Glycoproteins D) Lipopolysaccharides E) Lipoproteins

35. The biochemical property of lectins that is the basis for most of their biological effects is their ability to bind to: A) amphipathic molecules. B) hydrophobic molecules. C) specific lipids. D) specific oligosaccharides. E) specific peptides. (2) Provide BRIEF answers to the following questions. (19 points) (A) What is the difference between general acid-base catalysis and specific acid-base catalysis? (Assume that the solvent is water.) (B) What is the role of the Major Histocompatibility Complexes 1 and 2 (MHC) in the immune response?

(C) Describe the events that occur upon oxygen binding by hemoglobin and how this leads to the cooperative effect. (D) Methanol (wood alcohol) is highly toxic because it is converted to formaldehyde in a reaction catalyzed by the enzyme alcohol dehydrogenase:

NAD+^ + methanol  NADH + H+^ + formaldehyde

Part of the medical treatment for methanol poisoning is to administer ethanol (ethyl alcohol) in amounts large enough to cause intoxication under normal circumstances. Explain this in terms of what you know about examples of enzymatic reactions. (E) The enzymatic activity of lysozyme is optimal at pH 5.2 and decreases above and below this pH value. Lysozyme contains two amino acid residues in the active site essential for catalysis: Glu^35 and Asp^52. The p K value for the carboxyl side chains of these two residues are 5.9 and 4.5, respectively. What is the ionization state of each residue at the pH optimum of lysozyme? How can the ionization states of these two amino acid residues explain the pH-activity profile of lysozyme?