1. Which of the following analytical methodologies yields the most accurate estimation of
the molecular mass of a protein?
A. Isoelectric focusing electrophoresis
B. MALDI mass spectrometry
C.SDS-polyacrylamide electrophoresis
D. Size-exclusion chromatography
E. ELISA assay
2. Which of the following solutions will have a pH close to 7.0?
pK of Acid[Conjugate Base] : [Acid]
A. 4 100:1
B. 5 1 : 10
C. 6 1 : 1
D. 7 10 : 1
E. 8 1 : 10
3.Human DNA contains hypervariable regions that contain simple sequences that are
repeated in tandem a variable number of times, i.e., they contain a variable number of
tandem repeats (VNTRs). Which ONE of the following features of VNTRs makes them
uniquely useful in genetics and forensics.
A. They are easily detected because of the repeated sequences.
B. They are easily detected because of the presence of specific restriction enzyme
sites.
C.They are easily separated by size on polyacrylamide gels.
D. The number of repeats is highly variable among individuals.
E. They are scattered throughout the genome.
4. All the following statements concerning the roles of H-bonds in biomolecules are correct,
EXCEPT:
A. H-bonds facilitate Watson-Crick pairing of bases in nucleic acids.
B. H-bonds are the primary stabilizing factor of a-helices in proteins.
C. The properties of H-bonds account for the fluidity of water at room temperature.
D. H-bonding characteristics of water are the thermodynamic driving force for
hydrophobic interactions between non-polar biomolecules.
E. H-bonds help stabilize biomolecules because their bond energies are
approximately the same as that for covalent bonds between the same atoms.
5. How many high-energy phosphate-bond equivalents are utilized in the process of
activation of amino acids for protein synthesis?
A. Zero
B. One
C. Two
D. Three
E. Four
6. If a completely radioactive double-stranded DNA molecule undergoes two rounds of
replication in a solution free of radioactive label, what is the radioactivity status of the
resulting four DNA molecules?
A. Half should contain no radioactivity.
B. All should contain radioactivity.
C. Half should contain radioactivity in both strands.
D. One should contain radioactivity in both strands.
E. None should contain radioactivity.
7.All of the following statements describing the structure and function of IgG antibodies
are true EXCEPT:
A. The light chains are covalently linked to the heavy chains by disulfide bonds.
B. The carboxyl-terminal domain of the heavy chain is involved in epitope binding.
C. Antigens bind to IgG molecules at sites on the variable regions of the heavy and
light chains.
D.Antibody specificity is provided by the hypervariable regions of the heavy and
light chains.
E. An intact IgG molecule contains two antigen binding sites.
8. All of the following statements about telomerase are correct EXCEPT:
A. The RNA component acts as a template for the synthesis of a segment of DNA.
B. It adds telomeres to the 5' ends of the DNA strands.
C. It provides a mechanism for replicating he ends of linear chromosomes in most
eukaryotes.
D. It recognizes a G-rich single strand of DNA.
E. It has a reverse transcriptase-like activity.
9. When proteins denatured in sodium dodecyl sulfate (SDS) alone are separated by
electrophoresis,
A. The resultant denatured proteins have a large net negative charge
B. The SDS binds hydrophobically to the proteins yielding a large net positive
charge
C. The disulfide bonds in the protein are reduced to free sulfhydryl groups
D. The direction of electrophoretic movement is positive to negative
E. Migration of proteins is based on the net charge of the native protein.
10. The apoprotein B (ApoB) gene is transcriptionally active in the liver and intestine and
encodes an mRNA of the same nucleotide length. In the liver the protein encoded by the
ApoB mRNA is ApoB100, a protein of approximately 100 kilodaltons. In the intestine the
the ApoB mRNA encodes ApoB48, a protein of approximately 48 kilodaltons. Which one
of the following steps in gene expression accounts for this tissue-specific difference in
the protein product of the ApoB gene.
A. Selective retention of specific exons present in pre-mRNA molecules (i.e.,
alternative splicing).
B. Selective use of two different polyadenylation sites.
C. Selective RNA editing.
D. Selective use of two different transcriptional promoters.
E. Selective use of two different translation start sites.
11. Patients suffering from vitamin C deficiency often have bleeding gums and wounds that
fail to heal properly. This is because vitamin C (ascorbic acid) is specifically required for
the reaction(s) involved in:
A. the synthesis of collagen cross-links
B. the synthesis of elastin cross-links
C. the hydroxylation of specific proline and lysine residues in collagen.
D. the glycosylation of hydroxylysine residues in collagen.
E. the conversion of procollagen to tropocollagen.
12. E. coli cells grown on a mixture of glucose and lactose selectively use glucose because:
A. Lactose provides less energy than glucose.
B. CRP is not present when glucose is available.
C. Glucose lowers cAMP levels, which reduces the level of the cAMP-CRP
complex.
D. Lactose cannot enter the cells, owing to glucose-induced inhibition of the lactose
transporter.
E. The synthesis of the lac repressor is elevated in the presence of glucose.
13. All of the following statements about molecular motors are true EXCEPT.
A. Both myosin and kinesin motors have a P-loop nucleotide binding site.
B. Intact skeletal muscle myosin has 6 polypeptide chains.
C. Kinesin and dynein attach to microtubules and move in opposite
directions on the microtubule.
D. Kinesin requires GTP as a primary energy source.
E. Kinesin, cytoplasmic dynein and myosin I all attach to lipid vesicles.
14. The direction of transcription of the following sequence of the tryptophan operon occurs
from left to right. What would be the base sequence of the mRNA produced?
5'...GCGGCGACGCGC...3'
3'...CGCCGCTGCGCG... 5'
A. 5'...GCGCGUCGCCGC...3'
B. 5'...GCGGCGACGCGC...3'
C. 5'...GCGCGTGCGGCG...3"
D. 5'...GCGGCGUCGCGC...3'
E. 5'...CGCGCTCGCCGC...3'
15. The posttranscriptional processing of rRNA involves which one of the following events?
A. Hydrolytic cleavage of portions of the primary transcript.
B. Addition of a guanylate cap with a 5' to 5' triphosphate bridge.
C. Addition of a polyA tail.
D. Displacement of lariat RNA with a ribose moiety containing 2', 3', and 5'
phosphate linkages.
E. Addition of CCA to the 3' terminus.
16. All of the following statements about disulfide bonds are correct EXCEPT:
A.Formation of a disulfide bond involves reduction of the cysteine residues.
B. A disulfide bond may be formed between 2 cystein-residues that are distant from
each other in the primary structure of a protein.
C. Disulfide bonds help to stabilize many extracellular proteins.
D. Two polypeptide chains maybe covalently linked by disulfide bonds.
E. Disulfide bonds in the C-terminal propeptide of collagen are involved in initiation
of triple helix. `
17. Degeneracy of the genetic code denotes the existence of:
A. Multiple codons for a single amino acid.
B. Codons consisting of only two bases.
C. Base triplets that do not code for any amino acid.
D. Different protein synthesis systems in which a given triplet codes for different
amino acids.
E. Codons that include one or more of the `unusual' bases.
18. The ß-pleated sheet is stabilized by the presence of.
A. side-chain electrostatic interactions
B. side-chain H-bonding
C. H-bonding between peptide bond atoms in adjacent strands
D. Disulfide bonds between adjacent amino acids
E. Hydrophobic interactions between side chains of adjacent amino acids
19. The function of signal recognition particles is to:
A. Cleave signal sequences.
B. Detect cytosolic proteins.
C. Direct the signal sequences to ribosomes.
D. Bind ribosomes to endoplasmic reticulum.
E. Bind mRNA to ribosomes.
20. Dideoxyinosine triphosphate, a compound derived from dideoxyinosine and used in the
treatment of AIDS, inhibits DNA synthesis by:
A. Blocking the base pairing of cytidine with guanosine.
B. Failing to be incorporated into a DNA chain.
C. Forming a covalent complex with DNA polymerase S.
D. Causing chain termination.
E. Promoting the cleavage of the DNA backbone.
21. All of the following statements about the structure and function of hemoglobin are true
EXCEPT:
A. The protoporphyrin ring in home has ionizable groups that form ionic bonds with
lysines in globin chains.
B. Oxygen binding to heme occurs at the 6th coordination position on the heme iron.
C. The proximal histidine (F8) binds at the 5th coordination position on the heme iron.
D. The form of hemoglobin expressed during the earliest stages of development has a
subunit composition of α2γ2
E. A major feature of the structural basis of cooperative oxygen binding to
hemoglobin is the breaking of ionic bonds in going from low to high affinity states
for oxygen.
22. What is the correct order of the following steps in protein synthesis?
(1) A peptide bond is formed.
(2) The small ribosomal subunit is loaded with initiation factors, messenger
RNA, and initiation aminoacyl-transfer RNA.
(3) The intact ribosome slides forward three bases to read a new codon.
(4) The primed small ribosomal subunit binds with the large ribosomal
subunit.
(5) Elongation factors deliver aminoacyl-tRNA to bind to the A site.
A. 1,2,3,4,5
B. 2,3,4,5,1
C. 4,5,1,3,2
D. 3,2,4,5,1
E. 2,4,5,1,3
23. Hemoglobin and myoglobin both have all of the following characteristics EXCEPT:
A. affinity for oxygen is lowered by bisphosphoglycerate binding
B. contain mostly alpha-helical secondary structure.
C. bind one molecule of heme per globin chain.
D. bind heme in a hydrophobic pocket.
E. For oxygen dissociation, hemoglobin exhibits a sigmoidal curve whereas
myoglobin displays a hyperbolic curve.
Questions 24 and 25
Molecularly cloned DNA sequences are rapidly becoming an important tool in medicine. They
can be used in the production of clinically important proteins, as diagnostic tools or in the
application of gene therapy of inherited genetic defects. The following list of terms refer to
some key aspect of molecular cloning technology. Match the appropriate terms with their
correct definition in the items.
A. Genomic library.
B. Plasmid vector.
C. Complementary DNA (cDNA)
D. Nucleic acid probes.
24. Independently replicating circular DNA molecules in bacteria that are used as carriers of
cloned genes for amplification in a bacterial host.
25.A collection of recombinant vectors that encompasses DNA inserts which represent the
entire complement of genomic DNA of the cell.
26. With regard to enzymes which of the following statements is False:
A. Phosphorylation of threonine, serine or tyrosine residues by kinases can result in
activation of an enzyme.
B.Activation of zymogens or proenzymes is always an intracellular event.
C. Calcium-mediated calmodulin binding is used to regulate different types of
enzyme activities within the cell.
D. Binding of homotropic effectors often results in positive cooperativity.
E. Binding of heterotropic effectors usually occurs at a site other than the active site.
27. Diphtheria toxin is often lethal in unimmunized persons because it:
A. Inhibits initiation of protein synthesis by preventing the binding of GTP to the
40S ribosomal subunit.
B. Binds to the signal recognition particle receptor on the cytoplasmic face of the
endoplasmic reticulum receptor.
C. Shuts off signal peptidase.
D.Blocks elongation of proteins by inactivating elongation factor 2 (EF2, or
translocase).
E. Causes deletions of amino acid by speeding up the movement of peptidyl-tRNA
from the A site to the P site.
28. Synthesis of tryptophan in E. coli is inhibited by:
A. Repressor binding of tryptophan.
B. Reduced levels of charged trp-tRNAs.
C. Decreased levels of glucose leading to an increase in cAMP levels.
D. Repressor release of tryptophan.
E. Binding of CRP-cAMP to the trp operon.
29. All of the following statements about collagen are true EXCEPT:
A. Each collagen chain has about 500 residues that are either Gly or Pro.
B. The collagen a-chain is an elongated helix that is stabilized by steric repulsion
between Pro residues.
C. Crosslinking allysine residues does not require an enzyme.
D. Galactose and glucose are covalently attached to hydroxylysine.
E.Procollagen spontaneously assembles into collagen fibrils after secretion from th
cell.
30.Which of the following enzymes cleaves DNA in a sequence-specific fashion?
A. DNA polymerase I.
B. Topoisomerase.
C. Restriction endonuclease.
D. DNA ligase.
E. DNA polymeraseIll.
31. Which of the following statements is TRUE?
A. Smooth muscle regulation involves phosphorylation of the myosin heavy chain.
B. In the absence of calcium the myosin crossbridge cycle is inhibited because
tropomyosin blocks the myosin-binding site on actin.
C. Exchange of ADP for ATP in myosin promotes strong binding of myosin to actin.
D. Binding of myosin to actin induces actin depolymerization thereby shortening the
length of the sarcomere.
E. The binding of calmodulin to the troponin complex regulates striated muscle
contraction.
32. Sigma factor is best described as a:
A. Subunit of RNA polymerase responsible for the specificity of the initiation of
transcription of RNA from DNA.
B. Subunit of DNA polymerise that allows for synthesis in both 5'→ 3' and 3' → 5'
directions.
C. Subunit of the 50S ribosome that catalyzes peptide bond synthesis.
D. Subunit of the 30S ribosome to which mRNA binds.
E. Factor that forms the bridge between the 30S and 50S particles constituting the
70S ribosome.
33. Which ONE of the following statements regarding 2,3 BPG is correct?
A. It increases the affinity of oxygen binding to hemoglobin.
B. It binds to negatively charged residues of hemoglobin such as aspartate and
glutamate.
C. The central cavity of hemoglobin can bind four molecules of BPG.
D. It has similar effects on myoglobin and hemoglobin.
E. It is a negative heterotropic effector of oxygen binding to hemeoglobin.
34. A polynucleotide is a polymer in which:
A. The two ends are structurally equivalent.
B. The monomeric units are joined together by phosphodiester bonds.
C. There are at least 20 different kinds of monomers that can be used.
D. The monomeric units are not separated by hydrolysis.
E. Purine and pyrimidine bases are the repeating units
35. The Bohr effect refers to which of the following:
A. Conversion of the hemoglobin from the T to the R form
B. Carbamylation of amino groups in hemoglobin
C. Binding of 2,3-BPG to the beta globin subunits
D. Binding of protons to hemoglobin to decrease its affinity for oxygen
E. Movement of iron into the plane of the heme upon binding oxygen to hemoglobin
36. Virgin B lymphocytes initially produce an immunoglobulin molecule (comprised of two
heavy and two light chains) that is attached to the cell surface via a membrane-anchoring
domain associated with the heavy chain protein subunits. Antigen stimulated B cells
produce a secreted form of the immunoglobulin that lacks the membrane anchoring
domain. Which one of the following steps in gene expression is altered to account for
the production of a secreted form of the immunoglobulin instead of the membrane-
anchored form.
A. RNA editing.
B. Selective use of alternative polyadenylation sites.
C. Selective use of alternative transcriptional promoters.
D. Selective use of alternative translation start sites.
E. Proteolytic removal of the membrane anchoring domain.
37. Enzymes speed up reaction rates by:
A. raising the free energy of the molecules in the transition state.
B. lowering the free energy released between the initial and final states.
C. lowering the free energy of activation required to reach the transition state.
D. making the change in free energy positive rather than negative.
38. Which aspect of retroviruses or the retroviral life cycle makes retroviral vectors
especially useful in human gene therapy applications?
A. The ability to accommodate large DNA inserts.
B. A highly efficient lytic cycle leading to the production of many recombinant
virions.
C. A highly efficient mechanism of cellular entry.
D. Efficient integration of proviral DNA into the host.
E. An RNA genome that eliminates the possibility of integration into the genome of
the infected cell.
39.Some of the enzymes utilized in DNA replication are:
(1)DNA-directed DNA polymerase.
(2)unwinding proteins.
(3)DNA polymerase I.
(4)DNA-directed RNA polymerase.
(5)DNA ligase.
What is the correct sequence of their use during DNA synthesis?
A. 2,3,4, 1,5
B. 2,4,1,3,5
C. 4,2,1,5,3
D. 4,2, 1,3,5
E.4,3,1,2,5
40. In the active site of the enzyme chymotrypsin, three residues (aspartic acid-102, histidine-
57, and serine-195) form what is referred to as a "catalytic triad." All of the following
statements regarding this "catalytic triad" are true EXCEPT:
A.Histidine-57 acts as a base catalyst by abstracting a proton from serine-195.
B. A covalent intermediate is formed between the substrate peptide and aspartic
acid-102.
C. Histidine-57 acts as an acid catalyst by donating a proton to a tetrahedral
transition state intermediate.
D. Diisopropylfluorophosphate irreversibly inhibits ehymotrypsin by forming a
covalent bond with serine-195.
E. Serine-195 performs a nucleophilic attack on a carbonyl group of a peptide bond.
41. The synthesis of proteins involved in the cellular uptake and storage of iron is regulated
by the concentration of iron in a cell. This regulatory process involves the interaction of
iron with a protein called the iron response element binding protein (IRE-BP). Which
one of the following events most accurately describes the consequences of decreased
cellular concentrations of iron.
A.IRE-BP is bound to IREs present in the 3' non-translated region of transferrin
receptor mRNA.
B. IRE-BP is bound to IREs present in the promoter region of the ferritin gene.
C. IRE-BP is released from IREs present in the 5' non-translated region of the ferritin
mRNA.
D. IRE-BP is released from IREs present in the 3' non-translated region of
transferrin receptor mRNA.
E. IRE-BP is bound to IREs present in the promoter region of the transferrin receptor
gene.
42. Which of the following statements about the peptide bond is/are correct?
1. The carbonyl and nitrogen groups of the peptide bond are polar.
2. The peptide bond forms a part of the backbone of a polypeptide.
3. The peptide bond has a partial double bond character.
4. The groups of the peptide bond can participate in the formation of an a-helix.
43. Which of the following statements about the a-helix are correct?
1. An α-helix is a secondary structure.
2.An α-helix is stabilized by H bonds between the amide H of one peptide group
and the carbonyl O of another.
3. The side chains of amino acids that form an α-helix project to the outside of the
helix.
4. The H bonds of an α-helix lie perpendicular to the axis of the helix.
BIOCHEMISTRY 2002
EXAM I
1 / B / 17 / A / 36 / B2 / E / 18 / C / 37 / C
3 / D / 19 / D / 38 / D
4 / E / 20 / D / 39 / B
5 / C / 21 / D / 40 / B
6 / A / 22 / E / 41 / A
7 / B / 23 / A / 42 / E
8 / B / 24 / B / 43 / A
9 / A / 25 / A
10 / C / 26 / B
11 / C / 27 / D
12 / C / 28 / A
13 / D / 29 / E
14 / B / 30 / C
15 / A / 31 / B
16 / A / 32 / A
33 / E
34 / B
35 / D
1