BioChem Unit 1
16. Which of the following is likely to increase the midpoint temperature of the melting curve for DNA? Decreasing the number of A-T pairs The incorporation of unusual bases Increasing the degree of homogeneity of the DNA sample Decreasing the number of G-C pairs None of the above
A
19. Which of the following is true for the double helical structure of DNA? DNA double helices are more stable than RNA double helices each strand of the helix contains unique information The major and minor grooves run in opposite directions The base sequence can only be read by proteins when the helix is opened up into a single-stranded form Electrostatic bonds are the primary stabilizing force for the double helix
A
20. Which of the following amino acids contains an imidazole group? Histidine Proline Tryptophan Glycine Asparagine
A
25. Which of the following amino acids can exist in four optically-active isomers? Threonine Alanine Cysteine Glycine Glutamine
A
5. Standard Watson-Crick base-pairing requires that guanine always pairs with? Cytosine Uridine 5-methylcytosine Thymine Adenine
A
A purely competitive inhibitor of an enzyme has which of the following kinetic effects? Increases Km without affecting Vmax
A
A purely noncompetitive inhibitor of an enzyme has which of the following kinetic effects? Decreases Vmax without affecting Km
A
All of the following statements about the a-helix are true EXCEPT? It is stabilized by hydrophobic interactions It is stabilized by minimizing unfavorable R-group interactions It is one type of secondary structure found in proteins It is stabilized by intramolecular hydrogen bonds Prolyl and glycyl residues tend to interrupt a-helix structure
A
In biochemical energetics and thermodynamics, the change in free energy of a reaction is indicated by the symbol? G
A
The Michaelis constant, Km, for an enzyme-catalyzed reaction can be determined from? Measuring reaction rates at different substrate concentrations
A
What is the difference between an active site and an allosteric site? An active site binds substrate, while an allosteric site binds a regulatory ligand
A
Whcih of the following statements is correct? Amino acid R-groups or side chains point above and below the plane of b-sheets The a-helix can be composed of more than one polypeptide chain b-sheets exist only in the antiparallel form The a-helix is stabilized primarily by ionic interactions between the side chains of amino acids Motifs are a type of secondary structure
A
Which of the following hemoglobin variants has a quaternary structure comprised of two alpha chains and two beta-2 glucose chains? HbA1c HbF HbA2 Hb Gower-2 HbA
A
Which of the following is the correct form of the Michaelis-Menten equation? v=Vmax[S]/Km+[S]
A
Which of the following statements concerning isoenzymes is CORRECT? Isoenzymes catalyze the same chemical reactions but have different amino acid sequences Isoenzymes will have the same kinetic properties, such as Km and Vmax All isoenzymes are located in the same tissue or cellular compartment Isoenzymes are composed of identical subunits Isoenzymes catalyze different chemical reactions
A
D
A substance that is NOT a blood buffer anion is? A. Phosphate B. Bicarbonate C. All of the above are blood buffer anions D. Chloride E. Proteinate
E
A weak acid can act as a buffer? A. At pH values = pK ±2 B. At pH values = pK ±0.1 C. At any pH value D. Only at body temperatures E. At pH values = pK ±1
D
An acidic solution could have a pH of? A. 7 B. 9 C. 10 D. 3 E. 14
b
At its isoelectric point (pI), a protein will have? A. None of the above B. Equal numbers of positive and negative charges C. Excess negative charges D. No positive or negative charges E. Excess positive charges
a
At pH 7.0, which of the following amino acid side chains will be positively charged? A. Lysine B. Glutamate C. Aspartate D. Histidine E. Cysteine
15. When lysine has a charge of +1? Only the e-amino group is protonated Both amino groups are protonated The carboxyl group is protonated all the ionic groups are protonated Only the a-amino group is protonated
B
17. Which of the following amino acids has three pK values between pH 2 and 12? Alanine Cysteine Threonine Glutamine Glycine
B
27. Which of the following bases is found in RNA? Thymine Uracil Adenine Guanine Cytosine
B
28. Which of the following is true of the peptide bond? It is readily broken by denaturing agents It is a type of amide linkage It is stabilized in a spiral configuration It has both a positive and negative charge at physiologic pH It is always favored in the cis configuration
B
29. Which of the following fatty acids contains 18 carbon atoms and two double bonds in its structure? Linolenic acid Linoleic acid Stearic acid Palmitic acid Oleic acid
B
9. Which of the following is true of lysine (pK1=2.2, pK2=9.0, pK3=10.5)? It is most likely to be found in the interior of a protein It will migrate toward the cathode (negative electrode) during electrophoresis at pH 7.0 It has a pI of 5.6 It has a phenolic side chain It has a charge of +1 when the carboxyl group is protonated
B
A mutation is most likely to alter the three-dimensional conformation of a protein if? It changes the amino acid at the amino-terminus It places a proline residue in the middle of an a-helix There is a substitution of a hydrophobic amino acid fro a hydrophilic amino acid It changes the amino acid at the carboxyl-terminus Valine is substituted for leucine
B
In an intact cell, the free energy change (delta G) associated with an enzyme-catalyzed reaction is frequently different from the standard free energy change (delta Go) of the same reaction because in the intact cell the? Reaction may be catalyzed by more than one enzyme Reactants are not at 1M concentrations Activation energy is different Reaction is always near equilibrium Enzyme my be regulated allosterically
B
Which is NOT a property of enzymes? Enzymes react with only specific substrates Enzymes alter the reaction equilibrium Enzymes accelerate the rate of a reaction Enzymes do not get used up in the reaction it catalyzes The same enzyme can catalyze both the forward and reverse reaction
B
Which of the following reactions is an example of an oxidation-reduction reaction? Methylmalonyl-CoA -> Succinyl-CoA Lactate + NAD+ -> Pyruvate + NADH + H+ Urea + H2O -> CO2 + 2NH3 Pyruvate + CO2 -> Oxaloacetate Pyruvate -> Acetaldehyde + CO2
B
Which of the following statements concerning denaturation of proteins is CORRECT? Denaturation is not produced by high concentration of chaotropes such as urea Denaturation results in the loss of secondary and tertiary structure Denaturation is always irreversible Denaturation increases the solubility or proteins in aqueous solution Denaturation results in the cleavage of peptide bonds
B
b
Buffer solutions? A. Cause an increase in pH when acids are added to them B. tend to maintain a relatively constant pH C. Will always have a pH of 7 D. Are rarely found in living systems E. Cause a decrease in pH when acids are added to them
10. Which of the following is NOT an L-amino acid in human proteins? Glutamine Leucine Glycine Threonine Cysteine
C
11. Which of the following statements concerning the process of denaturation of DNA is correct? Decreasing the temperature of a denatured DNA sample does not result in the reforming of the double helix Denaturation involves an increase in the number of hydrogen bonds between bases Denaturation can be monitored by hyperchromicity (increased absorbance at 260 nm) Denaturation can be achieved by decreasing the solution pH The melting curve is steeper for non-homogenous DNA samples (non-identical sequences)
C
21. Naturally-occurring fatty acids always contain which of the following types of double bonds? None of the above Only trans Only cis Mixtures of trans and amides Mixtures of trans and cis
C
22. Which of the following carbohydrates is a ketose sugar? Glucose Hexose Fructose Lactose Galactose
C
3. Which of the following will increase the melting point of a fatty acid? Increased cis-unsaturation None of the above Increased chain length Decreased chain length Increased unsaturation
C
Protein secondary structure is stabilized by which of the forces? Ionic bonds Disulfide bonds Hydrogen bonds Hydrophobic interactions van der Waals forces
C
Quiz Unit 1B 1. An amino acid with an ionic, polar side chain is? Leucine Alanine Lysine Serine Phenylalanine
C
Similarities between hemoglobin and myoglobin include which of the following? They are both located in the red blood cell (erythrocyte) 2,3-BPG reduces the oxygen binding capacity Heme is a prosthetic group Increased acidity reduces the oxygen binding Conversion from the "tense" to the "relaxed" conformation occurs when binding oxygen
C
The "sickling" of erythrocytes in sickle cell hemoglobin is due to polymerization of the hemoglobin molecules under conditions of? Decreased pH Increased concentrations of HbF Increased concentrations of the deoxygenated form of HbS Increased concentrations of the oxygenated form of HbS Increased concentrations of 2,3-bisphosphoglycerate
C
The Edman degration, performed using phenylisothiocyanate, is used to determine which of the following structural heirarchies? None of the above Secondary Primary Quaternary Tertiary
C
The Michaelis constant, Km, is? Dependent on the enzyme concentration Independent of pH Numerically equal to the substrate concentration that gives half-maximal velocity Increased in the presence of a noncompetitive inhibitor Numerically equal to 1/2 Vmax
C
The b-sheet is an example of which type of structure? Primary Tertiary Secondary None of the above Quaternary
C
Vmax and Km can be derived from the Lineweaver-Burke plot of the Michaelis-Menten equation. When V is the reaction velocity at substrate concentration S, the x-axis experimental data are expressed as? V S 1/S 1/V V/S
C
Which of the following statements concerning the structure of heme is correct? The proximal ligand is a histidine residue Heme is comprised of two pyrrole rings The fifth coordination position of heme is occupied by a lysine residue The heme prosthetic group contains a central Cu atom Hemoglobin and methemoglobin both bind oxygen with equal affinities
C
A
Carbonic anhydrase? A. Catalyzes the formation of CO2 from H2CO3 in the lungs B. Catalyzes the formation of carbaminohemoglobin from CO2 and hemoglobin C. Requires Fe2+ as a cofactor D. None of the above E. Is primarily present in plasma
12. Because of the abundance of hydroxyl groups, sugar molecules can form several types of carbohydrate derivatives which include? Amino sugars Sugar acids Deoxy sugars All of the above Sugar alcohols
D
13. Which one of the following types of bonds or interactions is LEAST important in determining the tertiary structure of proteins? Disulfide bonds Hydrogen bonds Hydrophobic interactions Coordination bonds (to ligands) Electrostatic bonds
D
14. Medium chain fatty acids contain how many carbon atoms? 2-4 4-6 12-15 6-10 15-20
D
30. Which of the following statements concerning DNA is correct? The Z-form of DNA is favored by long stretches of A and T nucleotides The A-form of DNA is the predominant natural form The purine and pyrimidine bases in DNA extend on the outside of the double helix The B-form of DNA is the predominant natural form The two grooves in the DNA double helix are equal in size
D
4. Which of the following amino acids contains an amide group? Threonine Glycine Cysteine Glutamine Tryptophan
D
6. Polymerization of glucose units to form glycosides requires the formation of which type of bond? Disulfide bond Amide bond Electrostatic bond Glycosidic bond Hydrogen bonds
D
Amino acid sequences are read in which direction? In any order Bottom to top Top to bottom Left to right Right to left
D
An enzyme that catalyzes the reaction A B changes the? Equilibrium constant Equilibrium concentration of A Entropy of the reaction Rate of both the forward and reverse reactions Heat of reaction
D
Hemoglobin exhibits which of the following structural hiearchies? Tertiary Secondary Quaternary All of the above Primary
D
How many a-amino functional groups are present in the pentapeptide Gly-Arg-Lys-Cys-His? 4 5 3 1 2
D
The presence of a noncompetitive inhibitor? Leads to a decrease in Vmax and Km Increases the steady-state concentration of ES Leads to an increase in Km without affecting Vmax Leads to a decrease in the observed Vmax Leads to both an increase in the Vmax of a reaction and an increase in the Km
D
The proteolytic action of the enzyme chymotrypsin is specific to which of the following amino acids? Carboxyl terminal amino acid Cysteine Arginine Tyrosine Glycine
D
Which of the following is NOT a common regulatory strategy for controlling the flux through a metabolic pathway? Allosteric regulation Gene regulation Compartmentation Non-Competitive inhibition Covalent modification
D
Which of the following is NOT one of the 6 IUB classes of enzymes? Ligase Hydrolase Isomerase Polymerase Transferase
D
Which of the following statements concerning enzymes is CORRECT? Enzymes chiefly bind substrates by noncovalent interactions Enzymes use salt bridges and hydrogen bonds to bind ligands specifically Changes in the specificity sub-site may change the type of substrate that is bound but not the chemistry that is catalyzed All of the above Enzyme active sites ensure that two substrates come together in the correct orientation for chemical reaction to occur.
D
Which one of the following correctly describes the expected products obtained when the polypeptide Arg-Gly-Phe-Leu-Met-Lys is treated as indicated? Treatment with trypsin gives three products Treatment with urea gives three products Treatment with HCl at 110 oC yields two products Treatment with cyanogen bromide yields two products Treatment with phenylisothiocyanate followed by mild acidification yields three products
D
D
Decreasing the pH of a solution from pH 7 to pH 5 results in an increase in the hydrogen ion concentration, [H+], by? A. 2 times B. 1,000 times C. 10 times D. 100 times E. 5 times
C
Determines blood H2CO3 concentration? A. NH3 B. H2CO3 C. Alveolar CO2 tension D. H2PO4- E. HCO3-
18. Reducing sugars are oxidized by Fehling's solution to produce a color reaction. Which of the following is NOT a reducing sugar? Fructose Lactose Glucose Galactose Sucrose
E
2. Which of the following statements concerning nucleotide structure is correct? The 4'-carbon position determines whether the nucleotide is a deoxyribonucleotide or a ribonucleotide One or more phosphate groups is attached to the 5'-carbon A purine or pyrimidine base is attached to the 3'-carbon position Nucleotide polymerization proceeds via the 5'-carbon A purine or pyrimidine base is attached to the 1'-carbon
E
23. Which of the following Greek symbols is used to designate the position of double bonds in a fatty acid structure? Gamma Beta Alpha Epsilon Delta
E
24. which of the following sugar alcohols is a derivative of glucose? Glycerol Xylitol Galactitol None of the above Sorbitol
E
26. In carbohydrate nomenclature, a triose contains how many carbon atoms? 4 2 6 5 3
E
7. Which of the following amino acid pairs have side chains that carry a negative charge at pH 7.0? Alanine and Glycine Aspartate and Asparagine Lysine and Arginine Glutamate and Glutamine Aspartate and Glutamate
E
8. Which of the following amino acids in involved in the formation of disulfide bonds? Proline Methionine Alanine Serine Cysteine
E
In the a-helix, the carbonyl oxygen in hydrogen-bonded to which amino nitrogen in the linear chain? n+5 n+1 n+3 n+2 n+4
E
In the study of enzymes, a sigmoidal plot of substrate concentration ([S]) versus reaction velocity (V) may indicate? Competitive inhibition Michaelis-Menten kinetics Noncompetitive inhibition Myoglobin binding to oxygen Cooperative binding
E
The chemical cyanogen bromide cleaves peptide chains on the carboxyl side of which amino acid residue? Cysteine Aspartic acid Arginine Lysine Methionine
E
The rate of an enzyme-catalyzed reaction was measured using several substrate concentrations that were much lower than Km. The dependence of reaction velocity on substrate concentration can best be described as? A constant fraction of Vmax Zero order with respect ot substrate Equal to Km Independent of enzyme concentration Proportional to the substrate concentration
E
Which of the following best describes a drug that acts as a noncompetitive inhibitor? It doesn't affect the Lineweaver-Burke plot It has a structure similar to a substrate It is usually irreversible It increases the steady-state concentration of the ES complex It acts by removing active enzyme from the substrate pool
E
Within the a-helix, the R-groups or amino acid side chains lie in which direction In the center of the helix Parallel to the direction of propogation of the helix Antiparallel to the direction of propogation of the helix In no particular angular pattern Perpendicular to the direction of propogation of the helix
E
C
For a weak acid, maximum buffering capacity occurs when? A. pH = Log pK. B. pH = -Log pK C. pH = pK D. pH = pK - 1 E. pH = pK + 1
b
For the following reaction, which of the following is a conjugate acid-base pair? H2PO4- (aq) + NH3 (aq) HPO42- (aq) + NH4+ (aq) A. H2PO4- and H2PO4- B. H2PO4- and HPO42- C. HPO42- and NH4+ D. None of the above E. H2PO4- and NH3
E
Hydrophilic compounds are soluble in water owing to the formation of? A. Ionic bonds B. Hydrophobic interactions C. Van der Waals interactions D. Covalent bonds E. Hydrogen bonds
E
In biochemistry, what is meant by the term "buffer"? A. A rubber ring to keep a flask from bumping the sides of a water bath. B. A safety margin below which a toxic compound has no effect. C. A hydration shell around a dissolved molecule. D. A group of atoms with low reactivity. E. A compound or solution that resists change in pH.
B
The Henderson-Hasselbalch equation is written as? A. pK = pH + Log [HA]/[A-] B. pH = pK + Log [A-]/[HA] C. pH = pK - Log [H+] D. pH = pK + Log [HA]/[A-] E. pH = pK + Ln [A-]/[HA]
B
The bicarbonate/CO2 pair is a good blood buffer, in vivo, at pH 7.4 because? A. It has a pK of 7.4 B. The partial pressure of CO2 in the blood is maintained at about 40mm of Hg upon addition of acid or base C. The ratio of HCO3-/H2CO3 varies between 0.5 and 1 D. None of the above E. Carbonic acid can dissociate 2 proteins
E
The concentration of hydrogen ions [H+] in a solution is expressed as the pH, which is numerically equivalent to? A. 1/Log [H+] B. Ln [H+] C. -Ln [H+] D. Log [H+] E. -Log [H+]
D
The enzyme, carbonic anhydrase, catalyses the reaction of carbon dioxide and water. Which of these is the correct equation? A. CO2 + H2O --Carbonic anhydrase--> OH- + HOCO2- B. None of the above. C. CO2 + H2O --Carbonic anhydrase--> OH- + HOCO D. CO2 + H2O --Carbonic anhydrase--> H+ + HCO3- E. H2CO3 + CO2 --Carbonic anhydrase--> H2C2O5
D
The isoelectric point [pI] for alanine is (pK1=2.3; pK2=9.9)? A. 11.4 B. 6.6 C. 9.9 D. 6.1 E. 2.3
C
The main form of carbon dioxide in the blood is? A. H2CO3 B. carbamino-plasma proteins C. HCO3- D. CO2 E. Carbaminohemoglobin
C
The most important buffer in extracellular fluid is? A. Acetate B. Phosphate C. Bicarbonate D. Chloride E. Protein
a
The partial negative charge at one end of a water molecule is attracted to a partial positive charge of another water molecule. What is this attraction called? A. A hydrogen bond. B. An ionic bond. C. A hydrophobic bond. D. A hydration shell. E. A polar covalent bond
D
What is the conjugate base of HCO3-? A. OH- B. H2CO3 C. H3CO3+ D. CO32- E. H2O
B
What is the pH of a buffer solution (HA and A-)containing 0.5M HA and 0.05M A- (pKa of HA=6.8)? A. 8.8 B. 5.8 C. 6.8 D. 4.8 E. 7.8
E
What is the pH of a buffer solution (HA and A-)containing 0.5M HA and 0.5M A- (pKa of HA=6.8)? A. 8.8 B. 4.8 C. 5.8 D. 7.8 E. 6.8
E
Which of the following amino acids could serve as the best buffer at pH 7.0? A. Arginine B. Glutamic acid C. Serine D. Valine E. Histidine
D
Which of the following best describes a titration curve? A. It can be used to determine the pK of a strong acid B. It generally plots as a straight line near the pK of each dissociable group C. It has an inflection point, which is the average of the pKs of all functional groups? D. It shows buffering of the change in pH near the pK of each dissociable group E. It is a plot of the change in pK with the amount of base added
A
Which of the following compounds is the strongest acid? A. Hydrochloric acid B. Lactic acid C. Phosphoric acid D. Acetic acid E. Carbonic acid
A
Which of the following groups of atoms is capable of forming hydrogen bonds? A. N-H and O=C B. N-C and O-H C. O-H and H-S D. C=O and O=C E. N-H and H-N
D
Which of the following solutions has the greatest concentration of hydroxyl ions(OH-)? A. Water (pH 7) B. Tomato puree (pH 4) C. Vinegar (pH 3) D. Sea water (pH 8) E. Black coffee (pH 5.5)
D
Which of the following statements best describes the difference between a strong electrolyte and a weak electrolyte? A. A strong electrolyte conducts an electrical current, but a weal electrolyte cannot B. A strong electrolyte is hydrophilic and a weal electrolyte is hydrophobic C. A strong electrolyte has a much larger equilibrium constant than a weak electrolyte D. A strong electrolyte does not form a conjugate base, but a weak electrolyte does have a conjugate base E. A weak electrolyte has an equilibrium constant that is dependent on the concentration, but the equilibrium constant for a strong electrolyte does not depend on concentration
Which of the following is an allosteric effector of hemoglobin oxygen binding? Oxygen 2,3-bisphosphoglycerate Carbon monoxide Hydroxyl anions Carbonic acid
b