Biochemistry National Board Exam Review

BIOCHEMISTRY NATIONAL BOARD EXAM REVIEW

Larry D. Barnes

Department of Biochemistry

University of Texas Health Science Center at San Antonio

June, 2004

Addendum, June 2005 (pg. 35)

The following questions (1-243) are from nine National Dental Board Examinations in Biochemistry-Physiology from 1978-1998. 1998 is the latest board exam released by the American Dental Association. This compilation of questions is intended to show the format, the subject areas generally covered, and the general level of knowledge required. Answers with some commentary are given beginning on page 29. The addenum begins on page 35 followed by answers.

BASIC CHEMISTRY

1. Which of the following characterizes exergonic reactions?
A. Decreased entropy
B. Increased enthalpy
C. Decreased enthalpy
D. Negative free energy change
E. Positive free energy change / 2. What thermodynamic parameter is a measure of randomness or disorder in a system?
A. Entropy
B. Enthalpy
C. Free energy
D. Potential energy
E. Activation energy
3. Atoms are isotopes of each other only if
A. their nuclei contain the same number of neutrons.
B. their atomic numbers are the same, but their mass numbers differ.
C. their mass numbers are the same, but their atomic numbers differ.
D. one is a beta emitter, but the other is an alpha emitter. / 4. Which of the following substances is LEAST polar?
A. Ethanol
B. Cholesterol
C. Palmitic acid
D. Glycocholic acid
5. Which of the following characterizes an asymmetric carbon?
A. A carbon atom with four identical groups attached to it.
B. A carbon atom with four different groups attached to it.
C. A carbon with at least one carboxyl and one amino group attached to it.
D. A carbon atom that has two heavy groups on one side and two light groups on the other. / 6. Which of the following compounds does NOT contain a high-energy bond?
A. ATP
B. Acetyl CoA
C. UDP-glucose
D. Glucose-6-phosphate
E. Phosphoenolypyruvate
7. Which of the following solutions has an osmotic pressure different from all the others?
A. 1 M glucose
B. 1 M sodium chloride
C. 1 M potassium nitrate
D. 1 N lithium iodide
E. 1 N hydrochloric acid

BUFFERS and pH

8. The Henderson-Hasselbach equations shows that
A. dilution of a buffer increases its pH.
B. pH = pka when an acid is 0.1 N
C. pH = pka when an acid is half neutralized.
D. pH is independent of the dissociation constant of the acid / 9. Which of the following represents the pH of a solution that has 10-5 M concentration of OH- ion?
A. 5
B. 7
C. 9
D. Determine only if the pKa is known.
E. Determinable only if the base composition is known.
10. If the pH becomes lower than the isoelectric point of a protein, then how will the protein respond in an electrophoretic system? It will
A. become denatured.
B. migrate to the negative pole.
C. migrate to the positive pole.
D. remain stationary and unchanged.
E. separate into its different monomeric forms. / 11. A physiologic buffer functions to
A. regulate the partial pressure of venous carbon dioxide.
B. carry fixed acid from the site of its elimination to the site of its production.
C. transport carbon dioxide from the site of its production to the site of its elimination.
D. minimize the increase in hydrogen ion concentration that accompanies cellular acid production.
E. maximize the decrease in hydrogen ion concentration that accompanies alkali formation.
12. All of the following function in buffer systems in the blood EXCEPT
A. NaCl.
B. H2C03.
C. NaHCO3.
D. Na2HPO4.
E. NaH2PO4. / 13. The buffer system most important in maintaining the physiological pH of plasma is
A. protein/proteinate
B. acetic acid/acetate
C. carbonic acid/bicarbonate
D. phosphoric acid/phosphate
E. hydroxybutyric acid/hydroxybutyrate

Bicarbonate/CO2

14. Neutralization of acids by saliva results mainly from which of the following salivary contents?
A. Mucin
B. Ammonia
C. Carbonate
D. Bicarbonate
E. Amino acids / 15. MOST of the CO2 in blood is combined as
A. H2C03.
B. HCO-3.
C. CH3 –COOH.
D. carbonic acid
E. carbaminohemoglobin.

Bicarbonate/CO2 (Continued)

16. The bicarbonate buffer system of the blood is very efficient because
A. bicarbonate is rapidly excreted by the kidneys.
B. bicarbonate is able to be stored in the tissue.
C. carbon dioxide is able to combine with hemoglobin
D. carbon dioxide forms a stable combination with base.
E. carbon dioxide is rapidly eliminated through the lungs. / 17. The normal blood bicarbonate-carbonic acid ratio is 20:1. A patient with a 10:1 ratio is in
A. compensated alkalosis.
B. compensated acidosis.
C. uncompensated alkalosis.
D. uncompensated acidosis.
E. none of the above. This patient’s ratio is within normal limits.
18. Absence of which of the following blood enzymes drastically reduces blood CO2 carrying capacity?
A. Carbonic anhydrase
B. Alkaline phosphatase
C. Pyruvate carboxykinase
D. Histidine decarboxylase
E. Serum glutamic-oxaloacetate transaminase

PROTEINS

19. Removal of a molecule of water between the carboxyl group of one amino acid and the amino group of a second amino acid results in formation of a
A. zwitterion.
B. polypeptide.
C. peptide bond.
D. hydrogen bond.
E. glycosidic bond. / 20. Which of the following BEST explains why proteins are able to buffer physiologic solutions over a wide range of pH?
A. They are macromolecules of high molecular weight.
B. They contain many functional groups with differing pKs.
C. They have unique tertiary structures that sequester hydrogen ions.
D. They have peptide bonds that are resistant to hydrolysis.
21. Denaturation usually destroys all of the following bonds in protein EXCEPT
A. hydrogen bonds.
B. covalent bonds.
C. hydrophobic bonds.
D. electrostatic bonds. / 22. Which of the following is the best method for determining the three-dimensional structure of protein?
A. Dialysis
B. Electrophoresis
C. X-ray diffraction
D. Ultracentrifugation
E. None of these

PROTEINS (Continued)

23. The amino acid that contributes to the tertiary structure of a protein by causing a bend when it occurs in the primary sequence is
A. leucine.
B. alanine.
C. proline.
D. tyrosine.
E. aspartic acid. / 24. A mucin is which of the following types of proteins?
A. Simple protein
B. Phosphoprotein
C. Chromoprotein.
D. Nucleoprotein.
E. Glycoprotein.
25. How will a protein respond in an electrophoretic system, should the pH become lower than the isoelectric point of the protein?
A. It will become denaturated.
B. It will migrate to the negative pole.
C. It will migrate to the positive pole.
D. It will remain stationary and unchanged.
E. It will separate into its different monomeric forms.

ENZYMES

26. Which of the following is true regarding enzymes?
A. Are not reusable
B. Are needed in large amounts
C. Catalyze endergonic reactions only
D. Increase the energy of activation of the reaction
E. Decrease the energy of activation of the reaction / 27. The optimum pH for an enzyme is the
A. isoelectric point of the enzyme.
B. pH of most rapid reaction rate.
C. pH at which the enzyme is most soluble.
D. pH of most rapid denaturation of the enzyme
28. The Km value of an enzyme is numerically equal to
A. half the maximum velocity expressed in moles/liter.
B. velocity of a reaction divided by substrate concentration.
C. substrate concentration in moles/liter necessary to achieve half the maximum velocity of a reaction.
D. maximum velocity divided by half the substrate concentration in moles necessary to achieve maximum velocity. / 29. In the relationship between the concentrations of substrate and the rate of an enzyme catalyzed reaction, the existence of a limited value (Vmax) of the reaction rate is due primarily to the
A. exhaustion of the substrate supply.
B. saturation of the enzyme with substrate.
C. inhibition of the enzyme by the reaction products.
D. denaturation of the enzyme at higher substrate concentrations.
E. balance between the increase in reaction rate with increasing substrate concentrations and accelerated destruction of the enzyme at higher substrate concentrations.

ENZYMES (Continued)

30. If the presence of a specific compound, C, increases the Km for an enzyme-substrate reaction, which of the following would be true about that enzyme?
A. C would be a competitive inhibitor of the enzyme.
B. C would be a noncompetitive inhibitor of the enzyme.
C. The velocity vs. [S] plot for the enzyme would be the same with or without C.
D. With C present, the enzyme would convert substrate to product faster.
E. With C present, it would take less substrate to drive the reaction to half-maximum velocity than without C. / 31. Protein kinase regulate the activities of key enzymes through which of the following?
A. Oxidation
B. Hydrolysis
C. Acetylation
D. Phosphorylation
E. Dephosphorylation
32. ATP inhibits phosphofructokinase even though ATP also is a substrate for the enzyme. Which of the following types of inhibition BEST explains this phenomenon?
A. Allosteric
B. Competitive
C. Irreversible
D. Uncompetitive
E. Noncompetitive / 33. Enzymes for electron transport reactions are most active and concentrated in which of the following structures of the animal cell?
A. Nuclei
B. Lysosomes
C. Microsomes
D. Mitochondria
E. All of the above
34. Sodium fluoride inhibits glycolysis by affecting
A. amylase
B. enolase
C. phosphatase
D. phosphorylase / 35. Which of the following enzymes converts trypsinogen to trypsin?
A. Enterokinase
B. Peptidase
C. Secretin
D. Pepsin
36. Two enzymes that have been postulated to play very important roles in calcification are
A. enolase and phosphorylase.
B. alkaline phosphatase and catalase.
C. pyrophosphatase and carbonic anhydrase.
D. pyrophosphatase and alkaline phosphatase.
E. carbonic anhydrase and alkaline phosphatase. / 37. Which of the following enzymes is essentially absent from normal mammalian muscle?
A. Glucokinase
B. Phosphorylase
C. Glucose-6-phosphatase
D. Glucose-6-phosphate isomerase
E. Glucose-6-phosphate dehydrogenase

ENZYMES (Continued)

38. Dental plaque arises primarily as a result of enzymatic reactions using which of the following?
A. Sucrose and lipid
B. Sucrose and saliva
C. Glucose and saliva
D. Glucose and protein / 39. Which of the following liver enzymes, absent from other tissues, gives the liver an advantage over other cells in taking up glucose after a meal?
A. Glucokinase
B. Aldolase
C. Hexokinase
D. Enolase
E. Glucose-6-phosphatase

COLLAGEN

40. The most abundant protein (by weight) in which the human body is
A. elastin.
B. keratin.
C. albumin.
D. collagen.
E. chondroitin. / 41. Alpha-ketoglutarate, oxygen, and ascorbic acid are essential for which of the following processes?
A. Incorporation of proline
B. Hydroxylation of proline
C. Gamma-carboxylation of proline
D. Oxidative deamination of lysine
E. Activation of procollagen peptidase
42. Which of the following statements concerning collagen is INCORRECT?
A. Collagen has a trihelical structure.
B. The molecular weight of collagen is above 100,000
C. Hydroxyproline is incorporated into the molecule by tRNA.
D. Destruction of collagen can be caused by collagenases.
E. Collagen contains both hydroxyproline and hydroxylysine residues. / 43. Hydroxylation of proline and lysine during collagen biosynthesis occurs
A. after translation.
B. in the mitochondrial matrix.
C. before formation of their respective amino acyl-tRNA’s.
D. while proline or lysine is bound to the peptidyl (P) site on the ribosome.
44. The major protein produced by the odontoblast and contained in the organic matrix of dentin is
A. chitin.
B. keratin.
C. elastin.
D. collagen.
E. cellulose. / 45. Which of the following do elastin and collagen have in common?
A. Easily stretched
B. Absence of proline
C. Disulfide crosslinking
D. Triple helix structure
E. About one-third glycine

HEMOGLOBIN

46. The physiologic importance of hemoglobin lies in its ability to combine
A. irreversibly with oxygen and CO2.
B. reversibly with oxygen at the ferric heme prosthetic group.
C. irreversibly with oxygen at the ferrous heme prosthetic group.
D. reversibly with oxygen at the ferrous heme prosthetic group.
E. None of the above / 47. Which of the following is NOT a part of the hemoglobin molecule?
A. Iron
B. Protein
C. Magnesium
D. Histidine
E. Pyrrole ring
48. Assuming that P50 = 26 torrs, under conditions where pO2 = 30 torrs, the average number of O2 molecules bound per hemoglobin molecule is closest to
A. 0.5.
B. less than 1.
C. almost 2.
D. greater than 2.
E. greater than 3. / 49. The affinity of hemoglobin for oxygen diminishes as which of the following is decreased?
A. pH
B. CO2
C. Temperature
D. Hydrogen ion concentration
E. 2, 3 bisphosphoglyceric acid (BPG)
50. The consequence of appreciable conversion of hemoglobin to methemoglobin is
A. a significant increase in carbon dioxide combining power.
B. a significant decrease in carbon dioxide combining power.
C. no effect on the ability of blood to pick up oxygen.
D. a noticeable increase in the ability of blood to pick up oxygen.
E. a noticeable decrease in the ability of blood to transport oxygen. / 51. Compared with hemoglobin A, the substitution of a valine for a glutamic acid residue in hemoglobin S results from
A. a genetic mutation
B. irradiation of hemoglobin A.
C. proteolytic action in the liver.
D. exposure to low oxygen tension.

PROTEIN SYNTHESIS

52. The process by which genetic information flows from RNA to protein is
A. mutation.
B. replication.
C. translation.
D. transcription. / 53. Which of the following enzymes or processes ensures that the correct amino acid is incorporated for a particular codon during protein synthesis?
A. Amino Acyl-tRNA synthetase
B. Ribosomal protein synthesis
C. Post-transcription splicing
D. RNA synthetase
E. Helicase
54. Polyuridylic acid in a cell-free system capable of protein synthesis results in production of polyphenylalanine. In this system, polyuridylic acid functions as
A. DNA.
B. transfer RNA.
C. messenger RNA.
D. ribosomal RNA.
E. mitochondrial RNA. / 55. The termination of synthesis of a polypeptide is believed to involve
A. nonsense codons.
B. anticodon-codon interaction.
C. tRNA which cannot bind amino acids.
D. hydrolysis of messenger RNA.
E. none of the above.
56. In prokaryotic protein synthesis, the elongation factor G serves to
A. form the initiation complex.
B. facilitate the binding of Fmet tRNA.
C. translocate the growing peptide chain and to move the ribosome along the mRNA.
D. prevent the larger ribosomal subunits from binding with those that are smaller. / 57. Streptomycin is an antibiotic which inhibits the process of
A. translation in eukaryotes.
B. translation in prokaryotes.
C. transcription in eukaryotes.
D. transcription in prokaryotes.
E. DNA replication in prokaryotes.
58. Each of the following represents an amino acid found in proteins and used directly in the reactions of protein synthesis EXCEPT one. Which one is this EXCEPTION?
A. Proline
B. Arginine
C. Tryptophan
D. Asparagine
E. Hydroxylysine

CARBOHYDRATES

59. Hydrolysis of sucrose by the enzyme sucrase yields
A. glucose only.
B. glucose and maltose.
C. glucose and fructose.
D. glucose and galactose.
E. fructose and maltose. / 60. 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. None of the above

CARBOHYDRATES (Continued)

61. Which of the following is NOT a monosaccharide?
A. Amylose
B. Glucose
C. Fructose
D. Glyceraldehyde
E. Glucuronic acid / 62. Some carbohydrates convert Cu2+ ions to Cu+ ions. This property is related to their ability to act as
A. a reducing agent.
B. an oxidizing agent.
C. both a reducing agent and an oxidizing agent.
D. neither a reducing agent nor an oxidizing agent.
63. What linkages occur in glycogen at branch points between glucose units?
A. Aplpha-1,4
B. Alpha-1,6
C. Beta-1,3
D. Beta-1,4
E. Beta-1,6 / 64. How many anomeric carbons are present in a fructose molecule?
A. 0
B. 1
C. 2
D. 5
E. 6
65. Carbohydrate is stored in the body principally as
A. glucose.
B. maltose.
C. sucrose.
D. glycogen.
E. glycosaminoglycans. / 66. Which of the following molecule features contributes to the water-binding properties of proteoglycans?
A. The carboxyl groups acting as buffers
B. Central hyaluronate (a helix) trapping water within
C. The space between the core proteins and the hyaluronate being highly charged.
D. The large number of alcohol groups on the polysaccharide chaining H-bond to water.
E. The large number of serine and theronine residues in the core protein offering H-bonding sites.
67. Which of the following functions as part of the extracellular matrix?
A. Mucin
B. Heparin
C. Collaginase
D. Chondroitin sulfate
E. Dolichol phosphate / 68. Each of the following is a glycosaminoglycan EXCEPT one. Which one is this EXCEPTION?
A. Chondroitin sulfate
B. Dermatan sulfate
C. Hyaluronic acid
D. Heparan sulfate
E. Keratin
69. Glycosaminoglycans function as important structural components of
A. glycogen.
B. nucleic acids.
C. hyaluronidase.
D. connective tissue. / 70. The carbohydrate in highest concentration in resting muscle is
A. glucose.
B. lactose.
C. sucrose.
D. glycogen.
E. inositol.

CARBOHYDRATES (Continued)

71. The most biologically important physiochemical property of connective tissue which is regulated by its mucopolysaccharide molecules is
A. viscosity.
B. buffering capacity.
C. solubility in dilute acides.
D. supersaturation with calcium ions.

NUCLEIC ACIDS

72. Which of the following is a pyrimidine base that is present in RNA but is NOT present in DNA?
A. Uracil
B. Guanine
C. Thymine
D. Adenine
E. Cytosine / 73. Which of the following bonds link the monomeric units of nucleic acids?
A. Ionic
B. Peptide
C. Thioester
D. Glycosidic
E. Phosphodiester
74. In the DNA molecule, guanine on 1 strand is joined to cytosine on the complementary strand by which of the following bonds?
A. Amide
B. 1 hydrogen
C. 2 hydrogen
D. 3 hydrogen
E. Phosphodiester / 75. As DNA is denatured, each of the following events take place EXCEPT one. Which event is this EXCEPTION?
A. Total G-C content of total DNA increasing
B. UV light absorption increasing
C. Complementary strands becoming random coils
D. Base stacking becoming disrupted
E. Hydrogen bond breaking
76. Which of the following are NOT produced by the hydrolysis of nucleic acids?
A. Pentoses
B. Phosphates
C. Amino acids
D. Purine bases
E. Pyrimidine bases / 77. The function of which of the following types of nucleic acid is to activate and select specific amino acids for protein synthesis?
A. rRNA
B. mRNA
C. cDNA
D. tRNA
E. hnRNA
78. If the molar percentage of A (adenine) in a native DNA specimen is 22%, then what is the molar content of G (guanine)?
A. 22%
B. 28%
C. 44%
D. 56%
E. 78% / 79. The degenerate nature of the genetic code implies
A. a common tRNA for at least two amino acids.
B. that a remarkable degree of inaccuracy occurs in transcription.
C. the existence of multiple codons for each amino acid.
D. the existence of multiple species of ribosomes for control of messenger translation.

NUCLEIC ACIDS (Continued)

80. Transcription is the cellular process of making
A. new DNA.
B. RNA from DNA.
C. proteins from amino acids by way of RNA.
D. none of the above. / 81. Which of the following is true of the Tm (melting temperature) of a given DNA double helix?
A. Is a function of the base composition
B. Can be used to accurately predict its molecular weight
C. Can be measured by observing the change in chemical composition
D. Is higher if individual strands of the DNA double helix are parallel rather than antiparallel
82. DNA damage by ultraviolet light is due to
A. alkylation of the guanine in DNA.
B. excessive unwinding of the DNA molecule
C. frequent replacement in the DNA molecule of purines by pyrimidines.
D. induction of dimerization by way of covalent bonds between adjacent thymine groups. / 83. Each of the following is involved in gene cloning EXCEPT one. Which one is this EXCEPTION?
A. DNA ligase
B. RNA polymerase
C. DNA polymerase I
D. Restriction nucleases
E. Reverse transcriptase
84. Plasmid vectors suitable for cloning have which of the following characteristics?
A. Must be able to replicate synchronously with the host chromosome
B. Several unique recognition sequences for one restriction enzyme
C. Two genes conferring resistance to different antibiotics
D. Large size to facilitate plasmid’s entry into cells / 85. The polymerase chain reaction is MOST useful for which of the following?
A. Preparing enzymes that synthesize nucleic acids
B. Isolating the genome of an organism
C. Amplifying a specific DNA sequence
D. Separating polyclonal antibodies
E. Synthesizing RNA and DNA

LIPIDS