Biochem Exam 2
What is the fractional saturation of myoglobin at pO2 = 2.8 torr, if p50 = 2.8 torr? 2.80 1.00 0.28 0.50
0.50
What is the fractional saturation of myoglobin at pO2 = 7.2 torr, if P50 = 2.8 torr? 0.50 0.72 0.28 1.00
0.72
The pK1, pK2, and pKR of the amino acid lysine are 2.2, 9.1, and 10.5, respectively. The pK1, pK2, and pKR of the amino acid arginine are 1.8, 9.0, and 12.5, respectively. A student at SDSU wants to use ion exchange chromatography to separate lysine from arginine. What pH is likely to work best for this separation? 1.5 2.5 5.5 7.5 10.5
10.5
If a 10-fold rate enhancement requires a ∆G‡ of about 5.7 kJ/mol, what enhancement will 17.1 kJ/mol yield? 30-fold 100-fold 1000-fold 20-fold
1000-fold
If a 10-fold rate enhancement requires a ∆G‡ of about 5.7 kJ/mol, how much would a 100-fold rate enhancement require? 100 kJ/mol 57 kJ/mol 11.4 kJ/mol 5.7 kJ/mol
11.4 kJ/mol
Which of the following substances cannot be used to cleave peptide bonds in polypeptides? trypsin cyanogen bromide endopeptidases 2-mercaptoethanol pepsin
2-mercaptoethanol
Which reagent reduces disulfide bonds to sulfhydryl groups? performic acid 2-mercaptoethanol iodoacetate cyanogen bromide (CNBr) dansyl chloride
2-mercaptoethanol
Disulfide bonds can be cleaved using iodoacetate. dansyl chloride. 2-mercaptoethanol (β-ME). trypsin. phenylisothiocyanate.
2-mercaptoethanol (β-ME).
Which of the following is most likely true for an enzyme that displays maximal activity at pH 6.4? This enzyme has a metallic cofactor. A Glu or Asp residue is required for enzymatic activity. A His residue is required for enzymatic activity. This enzyme does not act as an acid and/or base catalyst.
A His residue is required for enzymatic activity.
Which of the following is a role of histidine in myoglobin? A histidine residue occupies the 6th coordination position of Fe2+. A histidine residue forms a hydrogen bond with oxygen. Histidine residues become protonated as part of the Bohr effect. Protonated histidine residues aid in BPG binding. All of the above.
A histidine residue forms a hydrogen bond with oxygen.
The amino acid sequence of which type of protein is likely to have changed the least during evolution? A protein that has extensive interactions with other proteins and with DNA. A protein fragment with no known function. A protein that has some interactions with other proteins. A protein that makes no important interactions with other proteins.
A protein that has extensive interactions with other proteins and with DNA.
A well-designed enzyme active site provides which of the following features? A. Complementarity of shape and chemical nature to the substrate(s). B. Proximity and correct orientation of substrates and catalytic groups. C. Complementarity of shape and chemical nature to the transition state. Both A and B but NOT C are correct. A, B and C are all correct.
A, B and C are all correct.
Which of the following amino acids is MOST likely to be a conservative substitution for glycine? Ala Leu Pro Thr
Ala
Which statement about insulin is correct? Insulin is composed of two polypeptides, the A chain and the B chain. Insulin contains an intrachain disulfide bond. Insulin contains interchain disulfide bonds. The A chain and the B chain of insulin are encoded by a single gene. All of the above are correct.
All of the above are correct.
The binding of one O2 to a molecule of hemoglobin results in: The release of any other O2 that may have bound earlier. A decrease in hemoglobin's ability to bind a second O2. An increased affinity for O2 in the remaining subunits (which have not yet bound O2). Dissociation of the hemoglobin subunits. The movement of hemoglobin to an organism's muscle tissue.
An increased affinity for O2 in the remaining subunits (which have not yet bound O2).
Which of the following statements about BPG and its effect on oxygen transport is NOT true: The effects of BPG also help supply the fetus with oxygen. A fetus obtains its O2 from the maternal circulation via the placenta. BPG binds more tightly to adult hemoglobin than to fetal hemoglobin thus facilitating the transfer of O2 to the fetus. BPG binds in hemoglobin's central cavity in the T state but not in the R state. Thus because it binds (and thus stablizes) the T state, BPG has a negative allosteric effect on hemoglobin's binding of oxygen. An intial response in adapting to a higher altitude is increased BPG synthesis in erythrocytes. This increase in BPG causes the O2-binding curve of hemoglobin to shift from its sea-level position to a higher affinity position facilitating better O2 absorption and transport at the elavated altitude. The presence of BPG in mammalian erythrocytes decreases hemoglobin's affinity for oxygen. BPG stands for D-2,3 bisphosphoglycerate, shown below:
An intial response in adapting to a higher altitude is increased BPG synthesis in erythrocytes. This increase in BPG causes the O2-binding curve of hemoglobin to shift from its sea-level position to a higher affinity position facilitating better O2 absorption and transport at the elavated altitude.
Which of the following could act as a nucleophile in an enzyme? An ionized sulfhydryl group A metal ion A protonated ε-amino group A protonated Schiff base
An ionized sulfhydryl group
The enzymatically inactive protein resulting from the removal of a protein's cofactor is referred to as what? Zymogen Proenzyme Apoenzyme Holoenzyme
Apoenzyme
The enzyme 2,3-BPG mutase produces 1,3-BPG in red blood cells. Which of the following amino acids would you predict to find in the active site of 2,3-BPG mutase? Phe Glu Arg Leu Asp
Arg
Which of the following is NOT a conservative amino acid substitution in a protein structure? Asn to Gln Asp to Glu Ser to Thr Ala to Val Arg to Phe
Arg to Phe
In two homologous proteins, which residue is most likely to replace a Glu residue as a conservative substitution? Asp Trp Met Ile Lys
Asp
You have purified a new peptide hormone. To determine its amino acid sequence you have digested the polypeptide with trypsin and in a separate reaction you have cleaved the polypeptide with cyanogen bromide. Cleavage with trypsin yielded 5 peptides that were sequenced by Edman degradation as shown in the following. 1. Ser-Leu 2. Asp-Val-Arg 3. Val-Met-Glu-Lys 4. Ser-Gln-Met-His-Lys 5. Ile-Phe-Met-Leu-Cys-Arg Cleavage with cyanogen bromide yielded 4 peptides that were sequenced by Edman degradation: 1. His-Lys-Ser-Leu 2. Asp-Val-Arg-Val-Met 3. Glu-Lys-Ile-Phe-Met 4. Leu-Cys-Arg-Ser-Gln-Met Determine the identity of the N-terminal amino acid after reconstructing the intact protein. Asp Ser His Glu Ile
Asp
Which of the following does NOT alter enzyme activity in a cell by changing the exact geometry of the active site? A. Allostery. B. Competitive inhibition. C. Phosphorylation. D. Increased gene expression. B and D.
B and D.
In the graph shown which of the following statements is TRUE concerning the "plateau" region of the curve? A. All the available substrate has been converted to product. B. The enzymes active site is saturated. C. The enzyme is in the tense state. A and C. A and B.
B. The enzymes active site is saturated.
Which of the following statements about 2,3-bisphosphoglycerate (BPG) binding is FALSE? BPG aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen. BPG requires a binding site containing multiple positively charged groups. BPG binds to hemoglobin at one site and lowers hemoglobin's affinity for oxygen at another site. BPG binds less tightly to fetal hemoglobin than to adult hemoglobin, thereby aiding oxygen transfer to a fetus.
BPG aids oxygen delivery to tissues by increasing the affinity of myoglobin for oxygen.
How does BPG decrease the affinity of hemoglobin for oxygen? BPG binding to hemoglobin stabilizes the oxy conformation. BPG blocks the oxygen binding sites directly. BPG binding to hemoglobin stabilizes the deoxy conformation. BPG reacts with oxygen to produce bicarbonate.
BPG binding to hemoglobin stabilizes the deoxy conformation.
Why is BPG essential for the delivery of O2 to the tissues? BPG stabilizes the T state conformation of hemoglobin. BPG stabilizes the R state conformation of hemoglobin. BPG stabilizes O2 binding to hemoglobin. BPG stabilizes the association of hemoglobin subunits.
BPG stabilizes the T state conformation of hemoglobin.
Why are chymotrypsin and subtilisin considered examples of convergent evolution? Because their polypeptide chains have the same fold, but their active sites have different residues. Because their polypeptide chains have different folds, but their active sites have identical residues. Because their polypeptide chains have different folds, and their active sites have different residues. Because their polypeptide chains have the same fold, and their active sites have identical residues.
Because their polypeptide chains have different folds, but their active sites have identical residues.
Why can enzymes be regulated? Because they have greater catalytic power than industrial catalysts. Because they are highly specific. Because they work at physiological temperatures and pressures. Because they are proteins.
Because they are proteins.
Which of the following is one way in which metal ions participate in the catalytic process? By shielding positive charge By binding to substrates to orient them properly for reaction By making water molecules more basic By mediating oxidation-reduction reactions through irreversible changes in the metal's oxidation state
By binding to substrates to orient them properly for reaction
Which of the following is TRUE about competitive inhibitors? A. Competitive inhibitors lower the KM and the Vmax of the enzyme. B. Competitive inhibitors structurally resemble the substrate and so they bind to the active site and become covalently attached to the enzyme. C. Transition state analogs often make better competitive inhibitors than do substrate analogs. A and C are both true. A, B and C are all true.
C. Transition state analogs often make better competitive inhibitors than do substrate analogs.
Select the statement that best matches the following: Troponin C Functional unit of the myofibril. Major component of the thick filament of the myofibril. Major component of the thin filament of the myofibril. Calcium binding protein. Chemical energy source for muscle contraction.
Calcium binding protein.
How is muscle contraction stimulated by calcium ions? Calcium ions are released from the sarcoplasmic reticulum and bind to tropomyosin, stimulating its ATPase activity Calcium ions are released from the sarcoplasmic reticulum and bind to actin, promoting its binding to myosin. Calcium ions are released from the sarcoplasmic reticulum and bind to troponin C, promoting the binding of myosin to actin. Calcium ions are released from the sarcoplasmic reticulum and bind to myosin, stimulating ATPase activity.
Calcium ions are released from the sarcoplasmic reticulum and bind to troponin C, promoting the binding of myosin to actin.
Which of the following includes two characteristics of enzyme-catalyzed reactions? Capacity for regulation and a high degree of substrate specificity Without regulation, but with a broad degree of substrate specificity Capacity for regulation and a broad substrate specificity Without regulation, but with a high degree of substrate specificity
Capacity for regulation and a high degree of substrate specificity
Which of the following statements is TRUE? The amount of energy released during a reaction determines the rate at which the reaction will occur. A reaction with a higher transition state energy will always occur more slowly than a reaction with a lower transition state energy. The change in Gibbs free energy () for a reaction is positive when energy is released. Enzymes speed up favorable reactions by inhibiting achievement of the transition state. Catalysts work by lowering the activation energy of a reaction.
Catalysts work by lowering the activation energy of a reaction.
What can be done to increase the rate at which a protein of interest moves down an ion-exchange chromatography column? Reduce the ion concentration in the eluant Add a small amount of a non-ionic detergents to the eluant. Change the pH of the eluant. Add a protease inhibitor to the eluant. Reduce the temperature of the eluant.
Change the pH of the eluant.
Select the statement the best matches that following: ATP Calcium binding protein. Chemical energy source for muscle contraction. Major component of the thin filament of the myofibril. Functional unit of the myofibril. Major component of the thick filament of the myofibril.
Chemical energy source for muscle contraction.
Which of the following provides evidence for the role of strain in the mechanism of action by lysozyme? Co-crystallization of lysozyme with NAM-NAG-NAM shows a distorted NAM at the D subsite. NAM binds favorably to the B and F subsites of lysozyme. Theoretical calculations indicate that lysozyme is very flexible. NAG lactone binds to the D subsite with only 9.2 kJ/mol greater affinity than does NAG.
Co-crystallization of lysozyme with NAM-NAG-NAM shows a distorted NAM at the D subsite.
In order to catalyze reactions, enzymes frequently require additional substances in their active site. What is the name for this family of substances? Coenzymes Essential ions Prosthetic groups Cofactors
Cofactors
Which statement expresses the correct relationship between cosubstrates, coenzymes, and cofactors? Cosubstrates are coenzymes that transiently bind to enzymes, while coenzymes are cofactors that are organic compounds. Coenzymes are cosubstrates that transiently bind to enzymes, while cofactors are coenzymes that are organic compounds. Cosubstrates are coenzymes that transiently bind to enzymes, while cofactors are coenzymes that are organic compounds. Coenzymes are cosubstrates that transiently bind to enzymes, while coenzymes are cofactors that are organic compounds.
Cosubstrates are coenzymes that transiently bind to enzymes, while coenzymes are cofactors that are organic compounds.
Which of the following statements about catalytic mechanisms of enzymes is TRUE? Enzyme catalytic mechanisms always require specific positioning of substrates and catalytic groups. Enzyme catalytic mechanisms always require the formation of covalent intermediates. Enzyme catalytic mechanisms always require prosthetic groups and R groups. Enzyme catalytic mechanisms always require the use of acidic and basic R groups.
Enzyme catalytic mechanisms always require specific positioning of substrates and catalytic groups.
Which statement best describes the model of "induced fit"? Enzyme-substrate binding induces enzyme specificity. Enzyme-substrate binding induces formation of the transition state, which reduces the free energy of the reaction. Enzyme-substrate binding induces a conformational change in the enzyme, such that the binding site better conforms to the shape of the substrate. Enzyme-substrate binding induces an increase in the reaction entropy.
Enzyme-substrate binding induces a conformational change in the enzyme, such that the binding site better conforms to the shape of the substrate.
Which statement describes why enzymes can increase the rate of a reaction? Enzymes make non-spontaneous reactions spontaneous. Enzymes decrease the activation energy of the reaction they catalyze. Enzymes make thermodynamically unfavorable reactions favorable. Enzymes decrease the of the reaction. All of the above statements are correct.
Enzymes decrease the activation energy of the reaction they catalyze.
Which of the following is FALSE with respect to an enzyme catalyzed reaction? Enzyme catalyzed reactions are superior to chemically catalyzed reactions because they are more specific and they lack side products. Enzymes increase a reaction rate by binding the transition state more tightly than the substrate(s). Enzymes increase the kinetic and thermodynamic favorability of a reaction. Enzymes lower the activation energy of a reaction to increase the reaction rate.
Enzymes increase the kinetic and thermodynamic favorability of a reaction.
Which one of the following statements about enzyme catalyzed reactions is FALSE? Many enzymes change shape upon substrate binding. Enzymes form complexes with their substrates. Enzymes lower the free energy change for the reactions they catalyze. Enzymes catalyze reactions at their active site.
Enzymes lower the free energy change for the reactions they catalyze.
Which statement explains why enzymes use cofactors in catalysis? Functional groups of protein side chains are extremely limited in chemical catalysis. Functional groups of protein side chains are incapable of participating in chemical catalysis. Functional groups of protein side chains are less suitable for catalysis of certain reactions, such as acid-base reactions. Functional groups of protein side chains are less suitable for catalysis of certain reactions, such as oxidation-reduction reactions.
Functional groups of protein side chains are less suitable for catalysis of certain reactions, such as oxidation-reduction reactions.
Select the statement that best matches the following: Sarcomere Major component of the thin filament of the myofibril. Chemical energy source for muscle contraction. Functional unit of the myofibril. Major component of the thick filament of the myofibril. Calcium binding protein.
Functional unit of the myofibril.
Identify the most conservative amino acid substitution, assuming that these two residues occur at the same position in two homologous proteins. Glu --> Ala Glu --> Leu Glu --> Asp Glu --> Lys
Glu --> Asp
Identify the least conservative amino acid substitution, assuming that these two residues occur at the same position in two homologous proteins. Glu --> Lys Glu --> Ala Glu --> Asp Glu --> Leu
Glu --> Lys
Why does heat inactivate enzymes? Heat breaks the peptide bonds that link the amino acid residues together. Heat causes dissociation of essential cofactors from the active site. Heat disrupts the weak, non-covalent interactions that determine protein 3-D structure. Heat decreases the free energy change of a reaction, making it less favourable.
Heat disrupts the weak, non-covalent interactions that determine protein 3-D structure.
Which of the following statements is FALSE with respect to hemoglobin's transition from the T state to the R state? BPG is not required to stabilize the R state. Contacts between side chains in the different subunits of hemoglobin change upon binding of oxygen to one subunit. Helix F changes its secondary structure in response to oxygen binding. The Fe2+ ion is pulled into the plane of the heme prosthetic group when oxygen binds to hemoglobin in the T state.
Helix F changes its secondary structure in response to oxygen binding.
Which of the following statments about Sickle Cell anemia is INCORRECT? The administration of hydroxyurea is an effective treatment for sickle-cell anemia. Sickle-cell anemia is caused from deoxyhemoglobin S forming insoluble filaments. Individuals who are heterozygous carriers of hemoglobin S in an area where malaria is prevalent are more likely to survive to maturity than individuals who are homozygous for normal hemoglobin. Hemoglobin S has a lower affinity for oxygen than normal adult hemoglobin (hemoglobin A). The mutation causing sickle cell anemia is that hemoglobin S contains Val rather than Glu at the sixth position of each beta chain.
Hemoglobin S has a lower affinity for oxygen than normal adult hemoglobin (hemoglobin A).
Which of the statements below about hemoglobin and myoglobin's oxygen binding is INCORRECT: The reason hemoglobin has a sigmoidal or S-shaped oxygen binding curve whereas myoglobin has a hyperbolic oxygen binding curve is because hemoglobin is a tetramer whereas myoglobin is a monomer. Hemoglobin has a Hill coefficient > 1 whereas myoglobin has a Hill coefficient < 1. Myoglobin has a higher affinity for oxygen than hemoglobin. In any binding system, a sigmoidal curve is diagnostic of a cooperative interaction between binding sites whereas a hyperbolic binding curve is an indication of a lack of cooperativity. The p50 of hemoglobin is nearly 10 times higher than that of myoglobin. The Hill coefficient (n) increases with the degree of cooperativity of a reaction: A Hill coefficient of 1 (n = 1) indicates no cooperativity, a Hill coefficient < 1 (n < 1) indicates negative cooperativity and a Hill coefficient > 1 (n > 1) indicates positive cooperativity.
Hemoglobin has a Hill coefficient > 1 whereas myoglobin has a Hill coefficient < 1.
Which of the following diseases is not caused by a mutation in hemoglobin? Hemolytic anemia Hemophilia Polycythemia Sickle-cell anemia
Hemophilia
Which of the following amino acyl side chains can participate in acid-base catalysis? Leu Ala Met His
His
Which of the following occurs in hemoglobin when blood pH is lowered? The proximal histidine becomes charged at lower pH, which weakens the binding of heme in its pocket. The distal histidine becomes charged at lower pH, resulting in a lower affinity of the heme. Histidine side chains at the subunit interface are charged at lower pH, forming salt bridges that stabilize the T state. Hemoglobin binds BPG with reduced affinity because histidine side chains in the central cavity of hemoglobin are charged at lower pH.
Histidine side chains at the subunit interface are charged at lower pH, forming salt bridges that stabilize the T state.
___________ is an example of a very slowly evolving protein. Histone H4 Hemoglobin Cytochrome c Fibrinopeptides None of the above
Histone H4
Which of the following statements is FALSE? Fetal hemoglobin has a weaker affinity for BPG than maternal hemoglobin, resulting in a shift of the oxygen-binding curve to the left. Actively respiring tissues have a relatively low pH and low pO2, which favors the T-state of hemoglobin. In fetal hemoglobin the central cavity is lined with more histidines than in adult hemoglobin, which results in preferential stabilization of the R-state. As pH decreases, the O2 binding curve of hemoglobin shifts to the right, because a greater proportion of hemoglobin molecules exist in the T-state at a given pO2.
In fetal hemoglobin the central cavity is lined with more histidines than in adult hemoglobin, which results in preferential stabilization of the R-state.
Fetal hemoglobin has a higher affinity for oxygen than maternal hemoglobin. Which of the following statements correctly outlines the mechanism behind this observation? In fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with lower affinity. In fetal hemoglobin, the residue Ser143 is mutated to His143, and so the protein binds BPG with greater affinity. In fetal hemoglobin, the residue Ser143 is mutated to His143, and so the protein binds BPG with lower affinity. In fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with greater affinity.
In fetal hemoglobin, the residue His143 is mutated to Ser143, and so the protein binds BPG with lower affinity.
Which of the following describes the effect of an enzyme on the initial velocity of a given reaction? Increase Decrease No change
Increase
Which of the following features in a Lineweaver-Burk plot is altered by a competitive inhibitor in an enzyme-catalyzed reaction? Intercept on the x-axis Intercept on the 1/Vo axis Intercept on the y-axis Intercept on the y-axis which is the 1/Vo axis Shape of the plot
Intercept on the x-axis
How does the sliding filament model explain the shortening of the sarcomere during muscle contraction? Interdigitating thin filaments slide past each other. Interdigitating thick and thin filaments compress by forming coiled coils. Interdigitating thick filaments slide past each other. Interdigitating thick and thin filaments slide past each other.
Interdigitating thick and thin filaments slide past each other.
Which term best describes the histidine F8 residue in myoglobin and hemoglobin? Variable residue. Invariant residue. Catalytic residue. Conservatively substituted residue. Homologous residue.
Invariant residue.
Which technique does NOT separate proteins on the basis of size? Gel filtration chromatography. Ultracentrifugation. Ion-exchange chromatography. SDS-Polyacrylamide gel electrophoresis.
Ion-exchange chromatography.
For an enzyme that displays Michaelis-Menten kinetics what is the effect of an uncompetitive inhibitor on Vmax? It may increase or decrease There is no effect It increases It decreases
It decreases
During vigorous exercise, the pH of blood passing through skeletal muscle decreases. How does this decrease affect the behaviour of hemoglobin? It increases O2 binding to hemoglobin, because it decreases the binding of BPG. It decreases O2 binding to hemoglobin, because it increases the binding of BPG. It increases O2 binding to hemoglobin, because it increases the binding of BPG. It decreases O2 binding to hemoglobin, because it decreases the binding of BPG.
It decreases O2 binding to hemoglobin, because it increases the binding of BPG.
Which of the following is TRUE about the distal histidine of hemoglobin? It is not conserved in myoglobin. It forms a strong covalent bond with the Fe2+ atom coordinated by heme. It covalently bonds heme into the hemoglobin subunit. It forms a hydrogen bond with bound oxygen. It prevents helix F from moving in response to oxygen binding.
It forms a hydrogen bond with bound oxygen.
For an enzyme that displays Michaelis-Menten kinetics, what is the effect of a competitive inhibitor on KM? It may increase or decrease It increases There is no effect It decreases
It increases
Which of the following statements is not true about the Bradford assay? It involves the absorbance of light in the uv region by phenylalanine, tryptophan, and tyrosine. It uses the dye Coomassie brilliant blue. It is more sensitive than a spectroscopic methods employing absorbance at 280 nm. It is an assay to determine the amount of a protein present in a sample. It involves an absorption maximum shift from 465 nm to 595 nm.
It involves the absorbance of light in the uv region by phenylalanine, tryptophan, and tyrosine.
Protein X binds reversibly to ligand Y such that X + YXY, and the molar concentrations of X, Y and XY are known. Which of the following represents the dissociation constant (K) for this reaction? K = [X][Y]/[XY] K = [XY]/[X][Y] K = [X] + [Y]/[X + Y] K = [XY]/[Y] K could not be determined with the information provided.
K = [X][Y]/[XY]
To catalyze a reaction, an enzyme must do which of the following? Raise the free energy of activation to a value above the free energy of the reactants and products. Lower the free energy of activation to a value below the free energy of the reactants and products. Raise the free energy of activation to a value above that of the uncatalyzed reaction. Lower the free energy of activation to a value below that of the uncatalyzed reaction.
Lower the free energy of activation to a value below that of the uncatalyzed reaction.
Which amino acid in an enzyme could be responsible for an observed enzyme catalyzed reaction at pH 9? Lys Ala Asp Glu
Lys
Select the statement that best matches the following: Myosin Functional unit of the myofibril. Major component of the thick filament of the myofibril. Major component of the thin filament of the myofibril. Calcium binding protein. Chemical energy source for muscle contraction.
Major component of the thick filament of the myofibril.
Select the statement that best matches the following: Actin Calcium binding protein. Chemical energy source for muscle contraction. Functional unit of the myofibril. Major component of the thick filament of the myofibril. Major component of the thin filament of the myofibril.
Major component of the thin filament of the myofibril.
______________ has emerged as a technique for protein sequencing. NMR spectroscopy Mass spectrometry Gel electrophoresis Phylogenetic analysis Limited proteolysis
Mass spectrometry
Which of the following is true for the maximal velocity of an enzyme-catalyzed reaction? Maximal velocity increases when pH increases. Maximal velocity is reduced in the presence of a transition state analog competitive inhibitor. Maximal velocity can be calculated from the initial rate of the reaction at a concentration of substrate that is equal to the KM. Maximal velocity is not affected by the presence of a noncompetitive inhibitor.
Maximal velocity can be calculated from the initial rate of the reaction at a concentration of substrate that is equal to the KM.
Which of the following is true for the maximal velocity of an enzyme catalyzed reaction? Maximal velocity increases when pH increases. Maximal velocity is reduced in the presence of a transition state analog inhibitor. Maximal velocity increases when pH increases and is reduced in the presence of a transition state analog inhibitor. Maximal velocity may be used to determine KM. Maximal velocity increases when pH increases and is reduced in the presence of a transition state analog inhibitor. Maximal velocity may be used to determine KM.
Maximal velocity may be used to determine KM.
Which technique has allowed the purification of proteins of very low natural abundance? Electrophoresis. Ion exchange chromatography. Enzyme-linked immunosorbent assay. Molecular cloning.
Molecular cloning.
Which of the following statements best explains the concept of geometric and electronic complementarity between enzyme and substrate? Molecules that differ from the substrate in shape or in distribution of functional groups cannot bind productively to the enzyme. Molecules that differ from the substrate in shape or in distribution of functional groups can bind productively to the enzyme. Molecules that are similar to the substrate in shape or in distribution of functional groups cannot bind productively to the enzyme. Molecules that differ from the substrate in shape or in distribution of functional groups can bind to the enzyme, but cannot function.
Molecules that differ from the substrate in shape or in distribution of functional groups cannot bind productively to the enzyme.
Which of the following statements about blood diseases is not true: Hemolytic anemia results from the lysis of erythrocytes. The bluish skin color associated with cyanosis is due to the presence of methemoglobin in the arterial blood. Mutations that increase hemoglobin's O2 affinity lead to increased numbers of erythrocytes in order to compensate for the less than normal amount of O2 released in the tissues - a condition named polycythemia. Most of the variant hemoglobins identified result from a single amino acid substitution in a globin polypeptide chain. Most mutations to hemoglobin observed in nature (i.e. hemoglobin variants) result in a lethal condition. Cyanosis is caused by mutations that favor the oxidation of Fe(II) to Fe(III). Mutations that destabilize hemoglobin's tertiary or quaternary structure, alter its oxygen-binding affinity (p50) and reduce its cooperativity result in diseased states.
Most mutations to hemoglobin observed in nature (i.e. hemoglobin variants) result in a lethal condition.
Which of the following statements about diseases of hemoglobin and the blood is not true: Mutations to that destabilize hemoglobin's tertiary or quaternary structure, alter its oxygen-binding affinity (p50) and reduce its cooperativity result in diseased states. Cyanosis is caused by mutations that favor the oxidation of Fe(II) to Fe(III). Most mutations to hemoglobin observed in nature (i.e. hemoglobin variants) result in a lethal condition. The bluish skin color associated with cyanosis is due to the presence of methemoglobin in the arterial blood. Most of the variant hemoglobins identified result from a single amino acid substitution in a globin polypeptide chain. Mutations that increase hemoglobin's oxygen affinity lead to increased numbers of erythrocytes in order to compensate for the less than normal amount of oxygen released in the tissues - a condition named polycythemia. Hemolytic anemia results from the lysis of erythrocytes.
Most mutations to hemoglobin observed in nature (i.e. hemoglobin variants) result in a lethal condition.
Which of the following statements about the structure of myoglobin is FALSE? The tertiary structure of myogobin is a compact, roughly spherical shape. Myoglobin contains all three types of secondary structure. Myoglobin contains a heme prosthetic group that is slotted into a hydrophobic pocket between -helix E and -helix F. A heme prosthetic group is tightly bound to myoglobin via a coordination bond.
Myoglobin contains all three types of secondary structure.
Which of the following statements most accurately explains why hemoglobin is able to deliver oxygen to myoglobin in the tissues? The iron in the heme group of myoglobin is Fe3+, which has a higher affinity for oxygen. Myoglobin has a hyperbolic oxygen binding curve, whereas hemoglobin has a sigmoidal oxygen binding curve. The presence of BPG in the red blood cells shifts the equilibrium towards the R state of hemoglobin. The pH of tissue/muscle is always higher than that of blood, which aids hemoglobin in giving up its oxygen.
Myoglobin has a hyperbolic oxygen binding curve, whereas hemoglobin has a sigmoidal oxygen binding curve.
For an enzyme that displays Michaelis-Menten kinetics, what is the effect on KM of doubling the concentration of substrate? Increase Decrease No effect
No effect
Which of the following methods of altering enzyme activity is irreversible? Binding of transition state analogs to enzymes. Binding of competitive inhibitors to enzymes. Binding of allosteric effectors to enzymes. Phosphorylation of enzymes. None of the above.
None of the above.
Which of the following statements is true regarding sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE)? SDS-PAGE separates nucleic acids on the basis of their charge. SDS-PAGE can be used to directly determine the size of fatty acids. Larger proteins move through the gel faster under the influence of the electric field in SDS-PAGE. None of the statements is true. SDS-PAGE separates proteins on the basis of their intrinsic charge and isoelectric point.
None of the statements is true.
Why are degradative enzymes a concern during protein purification? They are major components of most cells. It is generally impossible to inactivate them. They can co-purify with the protein of interest. Once released they degrade proteins present.
Once released they degrade proteins present.
Which of the following statements is FALSE regarding the interaction of oxygen with myoglobin? Oxygen is a ligand of myoglobin. Oxygen binds at the 6th coordination position of the Fe2+ ion in the heme. Oxygen binds reversibly and with high affinity to the heme prosthetic group. Oxygen is a homoallosteric effector of myoglobin.
Oxygen is a homoallosteric effector of myoglobin.
The peptide Leu─Cys─Arg─Ser─Gln─Met is subjected to Edman degradation. In the first cycle the peptide first reacts with phenylisothiocyanate under basic conditions. The product of this reaction is incubated with anhydrous trifluoroacetic acid and subsequently with an aqueous acid. What are the products generated in the first cycle. PTH─Leu, PTH─Cys, PTH─Arg, PTH─Ser, PTH─Gln, and PTH─Met PTH─Leu─Cys─Arg─Ser─Gln─Met PTH─Met and Leu─Cys─Arg─Ser─Gln─Met PTH─Leu─Cys and PTH─Arg─Ser─Gln─Met PTH─Leu and Cys─Arg─Ser─Gln─Met
PTH─Leu and Cys─Arg─Ser─Gln─Met
Why is decomposition of the transition state to products usually considered the rate-determining process of the overall reaction? The transition state is a highly-populated state. The transition state is a long-lived state. Passage through the transition state is very rapid, so the concentration of the transition state is large. Passage through the transition state is very rapid, so the concentration of the transition state is small.
Passage through the transition state is very rapid, so the concentration of the transition state is small.
The oxyanion hole in serine proteinases illustrates which of the following mechanisms of enzyme action? Reduction of the activation energy barrier. The role of serine side chains in proteolysis. Preferential transition state binding. Induced fit in substrate binding.
Preferential transition state binding.
Which of the following statements is not true about SDS-PAGE: In SDS-PAGE the relative mobilities of proteins vary approximately linearly with the logarithm of their molecular masses. SDS-PAGE can be used to determine the molecular mass of an unkown protein by electrophoresing it on the same gel as proteins of known molecular masses whose masses span the mass of the unknown protein. Because SDS disrupts noncovalent interactions between polypeptides, SDS-PAGE yields the molecular masses of the subunits of multisubunit proteins. PAGE stands for polyacrylamide gel electrophoresis. Proteins are separated based on their size, shape and electric charge at a given pH. SDS stands for the detergent sodium dodecyl sulfate that has the structure [CH3(CH2)10CH2OSO3-]Na+.
Proteins are separated based on their size, shape and electric charge at a given pH.
Which of the following is NOT normally one of the three stages of covalent catalysis? The withdrawal of electrons from the reaction center by the electrophilic catalyst The nucleophilic reaction between the catalyst and the substrate to form a covalent bond The elimination of the catalyst Proton transfer by the enzyme
Proton transfer by the enzyme
Structurally, myoglobin and hemoglobin are very similar proteins. In which of the following levels of structure do they differ most? Secondary structure. Tertiary structure. Quaternary structure. Primary structure.
Quaternary structure.
Which of these techniques is used to separate proteins mainly based on mass? polyacrylamide gel electrophoresis (in the absence of SDS) SDS-PAGE isoelectric focusing immunoblotting Western blotting
SDS-PAGE
Affinity chromatography Separation on the basis of size and shape. Separation on the basis of polarity. Separation on the basis of binding specificity. Separation on the basis of charge.
Separation on the basis of binding specificity.
Ion-exchange chromatography Separation on the basis of size and shape. Separation on the basis of polarity. Separation on the basis of charge. Separation on the basis of binding specificity.
Separation on the basis of charge.
Hydrophobic interaction chromatography Separation on the basis of charge. Separation on the basis of size and shape. Separation on the basis of polarity. Separation on the basis of binding specificity.
Separation on the basis of polarity.
Gel filtration chromatography Separation on the basis of polarity. Separation on the basis of charge. Separation on the basis of binding specificity. Separation on the basis of size and shape.
Separation on the basis of size and shape.
Which amino acid is most likely to act as a covalent catalyst in an enzyme active site? Met Ser Ala Ile
Ser
Which of the following is an example of a conservative amino acid substitution in a protein structure? Ser to Thr Gly to Trp Asp to Arg Cys to Met
Ser to Thr
Which of the following statements about sickle cell anemia is FALSE? Sickle cell anemia is a consequence of a conservative mutation in the β-globin gene. Sickle cell anemia is a genetic disease. The mutation in sickle cell anemia replaces a hydrophilic surface residue with a non-polar residue. In sickle cell anemia, hemoglobin molecules aggregate to form long fibers that distort the shape of the red blood cell.
Sickle cell anemia is a consequence of a conservative mutation in the β-globin gene.
In studying the structure of a new enzyme, you find that side chains of Phe, Leu, and Ile are directed into the active site. Which of the following can logically be proposed on the basis of this observation? The transition state intermediate in the reaction is likely to be small. The substrate for this enzyme is likely to be small. Some groups on the substrate are likely to be hydrophobic. This enzyme is likely to bind its substrate with induced fit to exclude water.
Some groups on the substrate are likely to be hydrophobic.
Which of the following is the BEST explanation for the frequent appearance of His side chains in enzyme active sites? The His side chain is able to act as both an acid and a base under physiological conditions. The His side chain is non-polar and therefore is typically located away from the surface of globular proteins. The His side chain plays a major role in non-covalent binding interactions with substrates. The His side chain is negatively charged.
The His side chain is able to act as both an acid and a base under physiological conditions.
What are the two conformations of hemoglobin? The R state (the conformation of deoxyhemoglobin) and the T state (the conformation of oxyhemoglobin). The T state (the conformation of dideoxyhemoglobin) and the R state (the conformation of deoxyhemoglobin). The T state (the conformation of myoglobin) and the R state (the conformation of deoxyhemoglobin). The T state (the conformation of deoxyhemoglobin) and the R state (the conformation of oxyhemoglobin).
The T state (the conformation of deoxyhemoglobin) and the R state (the conformation of oxyhemoglobin).
Which statement explains the basis of salting in and salting out? The addition of ions weakens ionic interactions between proteins, leading to greater solubility, but too many ions can deprive the protein of solvent leading to protein precipitation. The addition of ions strengthens ionic interactions between proteins, leading to greater solubility, but too many ions can deprive the protein of solvent leading to protein precipitation. The addition of ions weakens ionic interactions between proteins, leading to greater solubility, but too few ions can deprive the protein of solvent leading to protein precipitation. The addition of ions strengthens ionic interactions between proteins, leading to greater solubility, but too few ions can deprive the protein of solvent leading to protein precipitation.
The addition of ions weakens ionic interactions between proteins, leading to greater solubility, but too many ions can deprive the protein of solvent leading to protein precipitation.
One of the adaptations to high altitude is an increase in the concentration of BPG in red blood cells. What effect does this have on the oxygen binding curve of hemoglobin and why? The curve is shifted to the right, because hemoglobin has tighter oxygen binding. The curve is shifted to the left because hemoglobin binds oxygen more tightly. The curve is shifted to the left because hemoglobin has a lower K (dissociation constant). The curve is shifted to the right, because hemoglobin has a lower affinity for oxygen.
The curve is shifted to the right, because hemoglobin has a lower affinity for oxygen.
Which of the following is NOT a role of histidine in hemoglobin? Protonated histidine residues aid in BPG binding. The proximal histidine occupies the 5th coordination position of Fe2+. The distal histidine occupies the 6th coordination position of Fe2+. Histidine residues become protonated as part of the Bohr effect.
The distal histidine occupies the 6th coordination position of Fe2+.
Which of the following statements correctly describes the interaction between an allosteric protein and an allosteric effector? The effector binds non-specifically to one subunit and through induced fit initiates cooperativity between the subunits. The effector binds covalently at a specific site on the protein, causing a global change in shape. The effector activates the protein by causing it to switch from its T (low affinity) to R (high affinity) form. The effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation.
The effector binds reversibly at a specific site on one subunit of the protein, causing a global change in conformation.
Which of the following processes DOES NOT play a role in favouring formation of the transition state in enzyme catalyzed-reactions? Induced fit. The inclusion of additional chemical substances in the active site. The formation of non-covalent interactions between amino acid side chains and the transition state intermediate. The formation of covalent interactions between amino acid side chains and the co-substrate.
The formation of covalent interactions between amino acid side chains and the co-substrate.
Which of the statements below about hemoglobin's oxygen binding is INCORRECT: Oxygen binding causes a change in the quaternary structure of hemoglobin where hemoglobin changes quaternary structure from the T (tense) state that has a low affinity of oxygen to the R (relaxed) state that has a higher affinity of oxygen. The T --> R transition in hemoglobin subunits explains the difference in the oxygen affinities of oxy- and deoxyhemoglobin. In any binding system, a sigmoidal ligand binding curve (like hemoglobin's for O2) indicates an allosteric effect where there is cooperative interaction between binding sites and generally indicates that a protein has more than one subunit. Hemoglobin's sigmoidal oxygen binding curve is due to the T --> R transition: The sigmoidal curve results because of the switch from a low affinity oxygen binding hyperbolic curve in the T-state to a high affinity oxygen binding hyperbolic curve in the R-state. The binding of oxygen to hemoglobin in an example of positive cooperativity: Oxygen binding favors the T --> R transition switching hemoglobin from the low affinity for oxygen T-state to the high affinity for oxygen R-state. The hemoglobin tetramer can bind 4 molecules of oxygen and because of its positive cooperativity, the fourth O2 molecule binds with 4-fold greater affinity than the first. The cooperative binding of O2 by hemoglobin is an example of an allosteric effect (Greek: allos, other stereos, solid or space). Allosteric effects, in which the binding of a ligand at one site affects the binding of another ligand at another site, generally require interactions among subunits of oligomeric proteins.
The hemoglobin tetramer can bind 4 molecules of oxygen and because of its positive cooperativity, the fourth O2 molecule binds with 4-fold greater affinity than the first.
Which of the following is TRUE in competitive inhibition? The inhibitor binds covalently to the enzyme. The inhibitor binds at several different sites on an enzyme. The inhibitor binds reversibly at the active site. The inhibitor lowers the characteristic Vmax of the enzyme.
The inhibitor binds reversibly at the active site.
The presence of an uncompetitive inhibitor in an enzyme-catalyzed reaction will alter which of the following in a Lineweaver-Burk plot? Intercept on the x-axis The intercept on both axes Intercept on the y-axis Slope of the plot Shape of the plot
The intercept on both axes
A newly-identified protein has a sigmoidal curve in a graph of fractional saturation versus ligand concentration. What can be deduced about this protein? The protein has a constant high affinity for the ligand. The protein has primary, secondary and tertiary structure, but not quaternary. The dissociation constant (K) of the ligand is low. The protein binds the ligand cooperatively.
The protein binds the ligand cooperatively.
A newly-identified protein shows a sigmoidally-shaped curve in a graph of fractional saturation versus ligand concentration. Which of the following statements about that protein is TRUE? The protein undergoes conformational changes in quaternary structure when the ligand binds. The ligand binds irreversibly at a specific site on the protein, causing a global change in shape. The protein does NOT bind the ligand cooperatively. When the ligand binds to one subunit, the affinity of the other subunits for the same ligand remains the same.
The protein undergoes conformational changes in quaternary structure when the ligand binds.
If hemoglobin is in the 'T' state, what is the first component of the peptide chain that moves in response to oxygen binding? The proximal histidine The distal histidine The Fe2+ ion The heme group
The proximal histidine
Which of the following statements is true regarding enzymes? Lyases require ATP to catalyze the formation of bonds. The binding energy is the energy associated with substrate binding. The rate of a reaction is inversely proportional to the activation energy for the reaction. Histidine is not capable of acting as an acid or a base in general acid/base catalysis. Isomerases are the most common enzyme class
The rate of a reaction is inversely proportional to the activation energy for the reaction.
The difference in free energy between the substrate and product of a reaction catalyzed by Enzyme A is negative and small. What conclusions can be drawn about this reaction? The reaction is not spontaneous and is slow. The reaction is spontaneous and fast. The reaction is spontaneous but slow. The reaction is spontaneous and its speed is unknown from these data.
The reaction is spontaneous and its speed is unknown from these data.
Which of the following statements is false for an enzyme that follows Michaelis-Menten kinetics? The initial velocity of the reaction is dependent on substrate concentration. Maximal velocity occurs when the enzyme is entirely in the ES form. The relationship between substrate concentration and reaction rate is sigmoidal. The Michaelis-Menten equation assumes that ES maintains a steady state.
The relationship between substrate concentration and reaction rate is sigmoidal.
Which of the following statements about affinity chromatography is not true: In metal chelate affinity chromatography, the matrix contains metal ions ligands (like Zn2+ or Ni2+) so that proteins bearing metal-chelating groups (e.g., multiple His side chains) can be retained. The stronger the interaction between the ligand and the protein, the better the result of the affinity purification. In immunoaffinity chromatography, an antibody is attached to the matrix in order to purify the protein against which the antibody was raised. It is a very effective means of separation because one can "fish out" the target protein from a mixture of several proteins by exploiting its unique biochemical affinity for the ligand. A molecule (a ligand) that specifically binds to the protein of interest (e.g., a non-reactive analog of an enzyme's substrate) is covalently attached to an inert matrix. The bound protein can be eluted by washing the column with a solution containing a high concentration of free ligand or a solution of different pH or ionic strength.
The stronger the interaction between the ligand and the protein, the better the result of the affinity purification.
For an enzyme that displays Michaelis-Menten kinetics, what is the effect of a competitive inhibitor on Vmax? It increases It may increase or decrease It decreases There is no effect
There is no effect
What is the difference between trypsin, chymotrypsin, and elastase? They differ in their reaction mechanisms. They differ in their catalytic residues. They differ in their substrate specificities. They differ in the fold of their polypeptide chains.
They differ in their substrate specificities.
What is the primary role of nonmuscle actin in eukaryotic cells? They are stored in organelles, for future use in muscle function. They form microfilaments that are part of the cytoskeleton. They are stored to provide a source of energy. They form a protective barrier on the surface of the cell.
They form microfilaments that are part of the cytoskeleton.
Why does the concentration of BPG in red blood cells increase when humans are exposed to high altitudes? To neutralize the increased concentration of hydrogen ions produced when muscle works harder at high altitudes. To induce the production of more red blood cells. To allow hemoglobin to bind more oxygen at lower partial pressures of oxygen. To allow hemoglobin to release more oxygen at lower partial pressures of oxygen.
To allow hemoglobin to release more oxygen at lower partial pressures of oxygen.
What is the role of an enzyme in a biological reaction? To ensure that the product has a lower free energy than the substrate. To ensure that all of the available substrate is converted to product. To increase the rate at which substrate is converted to product. To make the free energy change () of the reaction highly negative. To preferentially bind the transition state intermediate such that it cannot be converted back to substrate.
To increase the rate at which substrate is converted to product.
Why does it take only a small amount of enteropeptidase to activate trypsinogen to trypsin? Enteropeptidase is highly efficient. Enteropeptidase is very stable. Enteropeptidase is highly specific. Trypsin can also activate trypsinogen.
Trypsin can also activate trypsinogen.
Which of the following is true regarding the effect of inhibitors on Michaelis-Menten reactions? Competitive inhibitors make it impossible to calculate the Vmax of an enzyme for its substrate. Noncompetitive inhibitors have no effect on apparent KM. Uncompetitive inhibitors decreases the apparent KM and decrease the apparent Vmax. Competitive inhibitors have no effect on Vo. Competitive inhibitors decrease the apparent KM.
Uncompetitive inhibitors decreases the apparent KM and decrease the apparent Vmax.
Which of the following must be known to calculate the kcat of an enzyme? The KM for the substrate. Enzyme concentration. Vmax for the substrate, enzyme concentration and KM for the substrate. Vmax for the substrate and enzyme concentration. Vmax for the substrate.
Vmax for the substrate and enzyme concentration.
Which of the following statements is FALSE? In its interaction with hemoglobin, oxygen is: homoallosteric effector. bound at the 6th coordination position of the Fe(II) ion in the heme. reversibly bound. a prosthetic group. a ligand.
a prosthetic group.
A radioimmunoassay requires an enzyme-linked antibody. a coupled enzymatic reaction. a radiolabeled antibody. a catalytic antibody. a radiolabeled standard protein that is used to compete for binding to the antibody.
a radiolabeled standard protein that is used to compete for binding to the antibody.
Adding additional salt to a protein solution can cause: an increase in solubility called 'salting in'. a decrease in solubility called 'salting out'. protein precipitation from solution. all of the above none of the above
all of the above
Although a protein's primary sequence can be inferred from the nucleotide sequence, modifications such as ______ can be determined most easily by tandem mass spectrometry followed by protein database searching. phosphorylation disulfide crosslinks glycosylation acetylation all of the above
all of the above
Which of the following represents the true protomer of hemoglobin? alpha alpha beta beta alpha2 beta2
alpha beta
Dansyl chloride is used for: polypeptide cleavage on the C side of Lys or Arg. polypeptide cleavage on the C side of Met. reduction of disulfide bonds between cysteine residues. amino-terminal determination. polypeptide cleavage on the C side of Glu.
amino-terminal determination.
An enzyme-linked immunosorbent assay requires a radioactive substrate. a radioactive standard for binding to the antibody. aromatic amino acids. an antibody that binds the protein of interest. a catalytic antibody.
an antibody that binds the protein of interest.
You are purifying a nuclease by affinity chromatography. To determine which fractions contain the protein of interest, you test samples of all fractions for their ability to break down DNA. This is an example of a binding assay. a biological assay. an enzyme assay. an immunological assay. none of the above
an enzyme assay
The quantitation of proteins due to their absorbance at ~280 nm (UV region) is due to the large absorptivity of the ________ amino acids. anionic dansylated cleaved polar aromatic
aromatic
Which reagent can be used to achieve the hydrolytic cleavage of the C-terminal residue of a polypeptide? 2-mercaptoethanol iodoacetate endopeptidase carboxypeptidase dansyl chloride performic acid enteropeptidase V8 trypsin
carboxypeptidase
What would be the order of elution (from first --> last) of the proteins carbonic anhydrase (pI = 7.0), carboxypeptidase B (pI = 6.2) and chymotrypsin (pI = 8.0) run on a CM (carboxymethyl) ion exchange column at pH 6.6 eluted with an increasing NaCl gradient: carboxypeptidase B and carbonic anhydrase will elute together followed by chymotrypsin. chymotrypsin, carboxypeptidase B, carbonic anhydrase. carboxypeptidase B, carbonic anhydrase, chymotrypsin. carbonic anhydrase, chymotrypsin, carboxypeptidase B. chymotrypsin, carbonic anhydrase, carboxypeptidase B.
carboxypeptidase B, carbonic anhydrase, chymotrypsin.
The pK1, pK2, and pKR of the amino acid histidine are 1.8, 9.3, and 6.0, respectively. The pK1, pK2, and pKR of the amino acid arginine are 1.8, 9.0, and 12.5, respectively. You have a mixture of histidine and arginine, how would you try to separate these two amino acids? anion exchange chromatography at pH 2 anion exchange chromatography at pH 4 cation exchange chromatography at pH 2 cation exchange chromatography at pH 4 cation exchange chromatography at pH 6
cation exchange chromatography at pH 6
Which chemical reagent promotes peptide bond cleavage on the C-side (carboxyl side) of Met residues? phenylisothiocyanate elastase 2-mercaptoethanol cyanogen bromide trypsin chymotrypsin performic acid
cyanogen bromide
Which of these reagents is commonly used to determine the number of polypeptides in a protein? iodoacetate dansyl chloride 2-mercaptoethanol (β-ME) cyanogen bromide DEAE
dansyl chloride
Proteins are often constructed from multiple segments of 40-200 amino acid residues, commonly called pseudogenes. hypervariable residues. protolytic fragments. domains. subunits.
domains.
Which expression containing the free energy of activation (∆G‡) is proportional to the rate of a reaction? +∆G‡ /RT e(-∆G‡ /RT) -∆G‡ /RT ln(∆G‡ /RT)
e(-∆G‡ /RT)
Enzymes that hydrolyze the internal peptide bonds (not the peptide bonds of the terminal amino acids) of a protein are classified as oxidoreductases. lyases. endopeptidases. nucleases. exopeptidases.
endopeptidases.
A protein that has had few changes in its amino acid sequence over evolutionary history is labeled a fibrinopeptide. evolutionarily conserved. random. a product of pseudogenes. phylogenetic.
evolutionarily conserved.
A phylogenetic tree depicts ___________ of proteins. folding patterns hypervariable residues invariable residues evolutionary relationships gene sequences
evolutionary relationships
Which of the following amino acids would be last to elute at pH 8.0 from an anion-exchange column? lysine alanine glutamic acid asparagine glycine
glutamic acid
You are trying to separate five proteins, which are listed below, by gel filtration chromatography. Which of the proteins will elute first from the column? cytochrome c (12 kDa) RNA polymerase (99 kDa) glutamine synthetase (621 kDa) interferon- (34 kDa) hemoglobin (62 kDa)
glutamine synthetase (621 kDa)
The acronym HPLC stands for hydrophobic protein liquid chromatography. high-performance liquid chromatography. hydrophilic partition liquid chromatography. high-priced liquid chromatography. hydrostatic process liquid chromatography.
high-performance liquid chromatography.
Which of the following amino acids has the most significant role in the molecular mechanisms of hemoglobin's function? tyrosine histidine lysine glutamate glycine
histidine
A first step in purifying a protein that was initially associated with fatty substances would be Coomassie Brilliant Blue dye staining. analytical ultracentrifugation. ELISA. Western blotting. hydrophobic interaction chromatography.
hydrophobic interaction chromatography.
A technique that can be used to separate proteins based primarily on the presence of non-polar residues on their surface is called ion-exchange chromatography. gel filtration chromatography. affinity chromatography. gel electrophoresis. hydrophobic interaction chromatography.
hydrophobic interaction chromatography.
Edman degradation can be used to identify the N-terminal amino acid of a polypeptide. identify the C-terminal amino acid of a polypeptide. separate the subunits of a multi-subunit protein. cleave a protein at specific sites. cleave disulfide bonds within a protein so that the individual polypeptides can be separated.
identify the N-terminal amino acid of a polypeptide.
Which of these techniques uses antibodies to detect very small amounts of specific proteins following separation by SDS-PAGE. immunoblotting silverstaining Coomassie Brilliant Blue staining ELISA RIA
immunoblotting
ELISA is an example of a(n): enzyme assay. biological assay. binding assay. immunological assay. none of the above
immunological assay
A technique that can be used to separate proteins based primarily on their pI is called ion-exchange chromatography. gel filtration chromatography. affinity chromatography. isoelectric focusing. hydrophobic interaction chromatography.
isoelectric focusing.
Protein sequences are customarily 'reconstructed' from sequenced fragments because protein purification invariably results in the fragmentation of the protein of interest. proteins are naturally and inevitably cleaved by proteolytic enzymes. proteins are composed of multiple subunits. large polypeptides cannot be directly sequenced. all of the above
large polypeptides cannot be directly sequenced.
Enzymes that perform group elimination reactions to form double bonds are called: isomerases. hydrolases. lyases. transferases. ligases.
lyases.
Which of the following amino acids would be first to elute at pH 8.0 from an anion-exchange column? lysine alanine glutamic acid asparagine glycine
lysine
SDS-PAGE separates proteins primarily due to differences in isoelectric point. mass. polarity. solubility. amino acid sequence.
mass.
A fast and common method for determining the protein concentration in column effluent is: tandem mass spectrometry. salting in with ammonium sulfate. drying a portion and weighing the solid. measuring light absorption at 280 nm. Edman degradation.
measuring light absorption at 280 nm.
Noncooperative binding is characterized by a Hill coefficient of what value? 0 < n < 1 n = 1 n > 1 n = 0
n = 1
Enzymes that perform oxidation-reduction reactions are called: transferases. hydrolases. isomerases. lyases. oxidoreductases.
oxidoreductases.
Which of the following triggers the transition from T state to R state (low to high affinity) in hemoglobin? movement of the proximal histidine. heme binding. oxygen dissociation. oxygen binding. subunit dissociation.
oxygen binding.
Which reagent cleaves disulfide bonds oxidatively? performic acid 2-mercaptoethanol iodoacetate cyanogen bromide (CNBr) dansyl chloride
performic acid
Hydrophobic interaction chromatography can be used to separate proteins based on differences in ionic charge. solubility. size. polarity. binding specificity.
polarity.
Endopeptidase V8 is used for: amino-terminal determination. polypeptide cleavage on the C side of Met. reduction of disulfide bonds between cysteine residues. polypeptide cleavage on the C side of Glu. polypeptide cleavage on the C side of Lys or Arg.
polypeptide cleavage on the C side of Glu.
Chymotrypsin is used for: reduction of disulfide bonds between cysteine residues. polypeptide cleavage on the C side of Met. polypeptide cleavage on the C side of Lys or Arg. polypeptide cleavage on the C side of Trp, Tyr or Phe. amino-terminal determination. polypeptide cleavage on the C side of Glu.
polypeptide cleavage on the C side of Trp, Tyr or Phe.
The positive charge on proteins in electrospray ionization mass spectrometry is the result of protons fired at the gas-phase protein molecules. protonated side chains of Asp and Glu residues. protonated side chains of Arg and Lys residues. a high pH. electrons fired at the gas-phase protein molecules.
protonated side chains of Arg and Lys residues.
Which of the following 'assays' would be most specific for a particular protein? Bradford assay UV absorptivity radioimmunoassay molar absorptivity amino acid analysis
radioimmunoassay
2-Mercaptoethanol is used for: polypeptide cleavage on the C side of Glu. reduction of disulfide bonds between cysteine residues. polypeptide cleavage on the C side of Met. polypeptide cleavage on the C side of Lys or Arg. amino-terminal determination.
reduction of disulfide bonds between cysteine residues.
The salting in of proteins can be explained by: salt counterions reducing electrostatic attractions between protein molecules. salt ions reducing the polarity of the solution. salt ions increasing the hydrophobic interactions. releasing hydrophobic proteins from nonpolar tissue environments. hydration of the salt ions reducing solubility of proteins.
salt counterions reducing electrostatic attractions between protein molecules.
A fast way for nature to generate new proteins is: generation of pseudogenes. mutation by neutral drift. shuffling protein domains or motifs. hypervariable positions. liberal substitution.
shuffling protein domains or motifs.
Which physical characteristic is not commonly used in protein separation? solubility stereochemistry size charge polarity
stereochemistry
Paralogous genes are genes that do not encode protein. genes of slowly evolving proteins. relics of genes that are not expressed. genes of rapidly evolving proteins. the results of gene duplication.
the results of gene duplication.
Which chemical reagent promotes peptide bond cleavage on the C-side (carboxyl side) of lysine and arginine residues if the next residue is not proline? chymotrypsin phenylisothiocyanate trypsin elastase performic acid 2-mercaptoethanol cyanogen bromide
trypsin
Which of these are commonly used to cleave peptide bonds in polypeptides? 2-mercaptoethanol (β-ME) dansyl chloride iodoacetate sodium dodecyl sulfate trypsin
trypsin