MW- Biochemistry

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Sucrase is an intestinal enzyme that cleaves sucrose into it’s constituents. What glycosidic bond is cleaved to release the glucopyranose and fructofuranose molecules? A. Beta 1 – Beta 4 linkage B. Alpha 1 – Alpha 4 linkage C. Alpha 1 – Beta 2 linkage D. Alpha 2 – Beta 1 linkage E. Alpha 1 – Alpha 6 linkage
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Benedict’s agent is a useful tool to determine if a patient is diabetic due to detection of sugars in urine. Which sugar would NOT be detected by Benedict’s agent? A. Sucrose B. Cellobiose C. Maltose D. Lactose E. Maltotriose
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Beta linkages are important in structural polysaccharides because: A. They are easily hydrolyzed by glycosidase enzymes B. They allow the chains to form compact coils C. They cause the chains to exist in an extended form thus allowing them to form fibers D. They cause the chains to absorb more water E. They can be formed by any hydroxy group in the monomer, whereas -linkages can only be formed by the anomeric cabon
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What is the difference between α-D-glucose and α-D-galactose? A. They are mirror images of each other B. They differ in the configuration of substituents at C-4 C. One is an aldose and the other is a ketose D. They are anomers E. One forms only O-glycosidic bonds, and the other forms only N-glycosidic bonds
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What is the major difference between glycogen and amylose? A. Glycogen contains only glucose, and amylose contains some fructose in addition to glucose B. Glycogen is a storage polysaccharide, and amylose is a structural polysaccharide of the extracellular matrix C. Glycogen is branched, and amylose is not. D. Glycogen contains some β-linkages, but amylose contains only α-linkages E. Glycogen is stored in the liver, and amylose is stored in skeletal muscle
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A deficiency of the enzyme lactase results in lactose intolerance, a condition characterized by flatulence, bloating and diarrhea. Lactase hydrolyzes lactose into which of the following? A. 2 molecules of racemic glucose B. 1 molecule of D-glucose and 1 molecule of D-galactose C. 2 molecules of racemic fructose D. 1 molecule of D-mannose and 1 molecule of L-glucose E. 1 molecule of D-glucose and 1 molecule of D-fructose
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A 10-carbon sugar has recently been isolated from the cell wall of a plant indigenous to the Dominican Rain Forest. It has been determined experimentally that this sugar does not exhibit the property of mutarotation. Which of the following is a reasonable explanation for this phenomenon? A. the sugar is a ketose B. the sugar is not a reducing sugar C. the sugar is an aldose D. the sugar is a monosaccharide E. the sugar does not rotate plane polarized light.
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The arrangement of sugars into D- and L- configurations is based upon their resemblance to D- and L- A. glycine B. glucose C. fructose D. glyceraldehyde E. histidine
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A student from West Africa, who is going to college in the United States, experiences digestive problems (bloating, diarrhea and flatulence) whenever she eats foods containing milk products. She is most likely deficient in splitting which type of chemical bond? A. A disulfide bond B. A glycosidic bond C. An ester bond D. A phosphodiester bond E. An amide bond
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A polypeptide has a primary structure of Lys-Ala-His-Asp-Val-Arg-Gly-Glu. What is the overall charge? A. +2 B. +1 C. 0 D. -1 E. +2
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Serum proteins have a very specific optimal pH and some will become denatured if there are slight deviations from it. After consuming a particular dipeptide, it becomes denatured upon contact with the extremely acidic gastric juices within the stomach. What would be the overall charge on this dipeptide containing Lys and Leu amino acids at normal and within a very acidic environment respectively? A. +1/ +1 B. +1/ 0 C. +1/ +2 D. -1/ 0 E. -2/ -1
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A sailor walks into your clinic displaying early signs of scurvy (skin changes, bleeding gums). Why does a lack of Vitamin C result in the degeneration of collagen fibers? A. Vitamin C is necessary as an anti-oxidant, removing any reactive oxygen species from attacking the collagen and breaking apart its protein structure B. Vitamin C is required to convert proline to hydroxyproline, increasing the number of hydrogen bonds within alpha-helices of collagen, fortifying the collagen network within connective tissue C. Vitamin C is an anti-oxidant, preventing the oxidation of Cys residues to maintain the integrity of disulfide bridges. These bridges hold collagen molecules together and fortify the collagen network found in connective tissue D. Vitamin C is required to convert proline to hydroxyproline, increasing the number of hydrogen bonds between collagen beta-pleated sheets, fortifying the collagen network within connective tissue E. Vitamin C does not play a significant role in collagen formation or maintenance
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During one of your clinical rotations, you hear about a patient who recently died (1-2 days) from Creutzfeld-Jacob disease. Curious, you saw physicians performing an autopsy within an isolated room and wearing heavy protection to prevent any infection. Why are the doctors afraid of an infection if the patient is already dead? A. The prion is not degraded, even after death, due to the change in the protein’s tertiary structure (normal is an alpha-helix, abnormal is beta-pleated sheet B. The prion is not degraded, even after death, due to the change in the protein’s secondary structure (normal is a beta-pleated sheet, abnormal an alpha-helix) C. A highly resistant virus is the cause of this disease, and can survive within the patient’s body up to a week after death D. The prion is not degraded, even after death, due to the change in the protein’s tertiary structure (normal is a beta-pleated sheet, abnormal an alpha-helix) E. The prion is not degraded, even after death, due to the change in the protein’s secondary structure (normal is an alpha-helix, abnormal is beta-pleated sheet)
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At pH 2, what would be the net charge on Lys? A. 1 B. +1 C. +2 D. 0 E. -2
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What is the net charge on glutamate at ph 13? A. +2 B. +1 C. 0 D. -1 E. -2
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Which of the following is true about the tertiary structure of proteins? A. Disulfide bonds are part of the tertiary structure B. Only proteins with more than one polypeptide subunit have a tertiary structure C. Proteins with tertiary structure do not contain α-helix or β-pleated sheet D. van der Waals interactions play no role in the tertiary structure E. Interactions between hydrophobic amino acid side chains are the most important to hold the tertiary structure together
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Histones are proteins that bind to negatively charged phosphate groups of DNA. An amino acid in the histones that can mediate this binding is which of the following? A. Valine B. Lysine C. Aspartate D. Cysteine E. Glutamate
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The protein albumin is a major buffer of the pH of the blood, which is normally kept between 7.2 and 7.4. Which of the following is an amino acid side chain of albumin that participates in this buffering range? A. Aspartate B. Histidine C. Tryptophan D. Glutamate E. Cysteine
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Which of the following statements does NOT describe the structure of globular proteins? A. the surface is hydrophilic. B. the interior is hydrophobic C. the polar side chains are hydrogen bonded to other groups or water D. hydrophobic side chains are densely packed within the interior. E. the structure of globular proteins is very similar to collagen.
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Which of the following statements about protein structure is correct? A. Proteins consisting of one polypeptide can have quaternary structure B. The formation of a disulfide bond in a protein requires that the two participating cysteine residues be adjacent to each other in the primary sequence of the protein C. The stability of quaternary structure in proteins is mainly a result of covalent bonds between the subunits D. The information required for the correct folding of a protein is contained in the specific sequence of amino acids in the primary structure
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Mutations can alter protein structure and lead to devastating diseases. Consider the following amino acid changes: 1. Phe to Trp 2. Asp to Glu 3 .Arg to Leu 4. Arg to Lys 5. Ser to Thr Which change is most likely to disrupt the folding of a globular protein? A. 4 B. 1 C. 5 D. 3 E. 2
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Which type of interactions (forces) found in proteins is most appropriately matched with the feature that follows: A. ionic bonds: α-helical secondary structure B. salt bridges: β-pleated sheet C. hydrogen bonds: covalent cross-links between polypeptide chains D. peptide bonds: association of subunits to form quaternary structures E. hydrophobic interactions: tertiary structure
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The secondary structure of proteins: A. Is maintained by hydrogen bonds B. Is present only in proteins consisting of two or more subunits held together by non-covalent forces C. refers to any hydrogen-bonded interaction found in proteins D. implies the presence of a non-protein moiety bound to the polypeptide E. Is found only in fibrous proteins
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A mutation has changed an isoleucine residue of a protein to glutamate. Which statement best describes its location in a hydrophilic exterior? A. On the surface since it is hydrophilic in nature B. Inside the core of the protein since it is hydrophobic in nature C. Anywhere inside or outside D. Inside the core of protein since it has a polar but uncharged side chain
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Glycine and proline are the most abundant amino acids in the structure of which of the following proteins? A. Hemoglobin B. Myoglobin C. Insulin D. Collagen
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Which of the following amino acids cannot take part in hydrogen bonding? A. Serine B. Cysteine C. Threonine D. Valine
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In scurvy, which amino acid that is normally part of collagen is deficient? A. Hydroxytryptophan B. Hydroxytyrosine C. Hydroxyalanine D. Hydroxyproline
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Which of the characteristics below apply to amino acid glycine? A. Optically inactive B. Hydrophilic, basic and charged C. Optically active D. Hydrophilic, acidic and charged
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Which of the amino acids below is the uncharged derivative of an acidic amino acid? A. Cysteine B. Tyrosine C. Glutamine D. Serine
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Enzymes allow reactions that might not normally occur to occur readily in the cell because enzymes act as very efficient catalysts. Which of the following is an important characteristic of the active site of all enzymes? A. The substrate binds due to multiple weak non bonding interactions B. All residues in the active site are contiguous in the primary structure C. It is located at the N-terminal end of the enzyme protein D. The product is released very slowly E. A serine residue is usually present
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Ethylene glycol, the major ingredient in antifreeze, is occaisionally consumed by alcoholics as a substitute for ethanol. Ethylene glycol is also a substrate for alcohol dehydrogenase (ADH) but the aldehyde product that is formed is highly toxic. Ethanol is often administered as a treatment in cases of ethylene glycol poisoning. What is the likely reason that ethanol is an effective treatment for ethylene glycol poisoning”? A. Ethanol is an allosteric effector of ADH in addition to being a substrate B. Ethanol combines with the toxic product formed by the reaction of ADH with ethylene glycol in a manner that renders it non toxic C. Acetaldehyde, which is produced by the reaction of ADH with ethanol, is of therapeutic value D. Ethanol induces another enzyme that is capable of metabolizing ethylene glycol E. ADH exhibits a much lower Km for ethanol than for ethylene glycol
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The rate of a Michaelis-Menton enzyme-catalyzed reaction was measured at several concentrations that produced much less than the half maximal velocity. Which of the following best describes the effect on reaction rate? A. The reaction rate increases exponentially as substrate concentration increases B. The reaction rate is gradually reduced by product inhibition C. Denaturation of the enzyme reduces the reaction rate D. The rate is linearly proportional to the substrate concentration E. The reaction rate shows zero order kinetics
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During a drug screening program, a researcher finds a chemical compound that decreases the activity of the enzyme monamine oxidase. A fixed dose of the drug reduces the catalytic activity of the enzyme by the same percentage at all substrate concentrations, with a decrease in Vmax. Which of the following best describes this drug? A. Positive allosteric effector B. Competitive inhibitor C. Suicide inhibitor D. Non competitive inhibitor E. Negative allosteric effector
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In non competitive inhibition, what is the effect of excess substrate? A. prevents binding of the inhibitor B. fails to alter the effect of the inhibitor C. yields maximal velocity D. excess substrate maximizes the inhibitory effect of the inhibit E. increase Km
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The statin drugs, e.g, Mevacor (Lovastatin), bind non covalently to the enzyme HMG-CoA reductase because they mimic the transition state of the enzyme. This means that they: A. are irreversible in their action. B. compete with the substrate HMG-CoA for binding to the active site C. are considered suicide inhibitors D. bind to the allosteric site of the enzyme. E. make the binding of the substrate appear tighter, i.e., appear to make Km of the enzyme smaller.
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Rilpivirine is a new NonNucleoside Reverse Transcriptase Inhibitor( NNRTI) approved by the FDA in 2011 to treat HIV infection.. It binds to a hydrophobic pocket proximal to the active site. What effect would Rilpivirine have on Vmax and Km ? A. No effect on Vmax and Km B. An increase in both Vmax and Km C. A decrease in both Vmax and Km D. A decrease in Km and an increase in Vmax E. A decrease in Vmax and no effect on Km
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The addition of compound X to an enzymatic reaction results in an inhibition of enzyme activity. One of the best ways to experimentally determine if compound X is a non competitive inhibitor is to determine: A. its binding affinity for the enzyme B. the effect of increasing [X] concentration on Vmax C. the ratio of enzyme to compound X D. the molecular weight of compound X E. if the enzyme is covalently modified.
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Competitive inhibition is used therapeutically to treat patients who have ingested ethylene glycol. Which of the following is NOT TRUE concerning competitive inhibition of an alcohol dehydrogenase catalyzed reaction? A. The inhibition cannot be overcome by increasing the concentration of the substrate B. The competitive inhibitor resembles the substrate C. The competitive inhibitor binds to the same site as does the substrate D. The inhibition can be overcome by increasing the concentration of the substrate
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Below is a list of five substrates and their corresponding Km values for enzyme Y. Based on this information which of the substrates has the highest affinity for Enzyme Y? A. Substrate A ( Km = 5.4 X 10-4) B. Substrate B ( Km = 2.1 X 10-6) C. Substrate C ( Km = 7.0 X 10-6) D. Substrate D ( Km = 1.5 X 10-5) E. Substrate E ( Km = 7.5 X 10-5)
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Metotrexate is an anti-cancer drug which competitively inhibits dihydrofolate reductase, an enzyme required, amongst other things, for DNA synthesis. In the presence of this drug A. the Vmax of the enzyme will be reduced B. the apparent Km will increase C. a Lineweaver-Burk plot will show parallel lines. D. the apparent Km will decrease E. the inhibitor will bind to both the free enzyme and the ES-complex
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The enzyme that catalyzes the following reaction belongs to which broad enzyme class? Protein + ATP— Phosphoprotein + ADP A. Isomerase B. Lyase C. Oxidoreductase D. Transferase E. Ligase
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Which of the following is characteristic for the active sites of enzymes? A. Nearly all amino acid side chains of the protein participate in catalysis B. The amino acid residues that form the active site are adjacent in the primary structure of the polypeptide C. The amino acid residues in the active site that bind the substrate are always the ones that catalyze the reaction D. In many cases the active site changes its conformation when the substrate binds E. In many cases, the initial binding of the substrate to the active site involves the formation of a covalent bond
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What is meant by the steady-state assumption that underlies the Michaelis-Menton relationship between substrate concentration and reaction velocity? A. The reaction velocity is linearly related to substrate concentration. B. The rate of breakdown of the enzyme-substrate complex equals the rate of formation of the complex C. The reaction velocity is independent of substrate concent D. The rate of formation of product equals the rate of disappearance of substrate E. The amount of enzyme remains constant
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