Download Medical School Biochemistry

1.
The effect of H+ on hemoglobin (Bohr effect) is to:
A.
B.
C.
D.
E.
2.
Osteogenesis imperfecta (OI) is a heterogeneous group of diseases in which there is a
defect in the synthesis of collagen. Some involve the synthesis of a mutated form of
collagen. Which of the following mutations would most likely be a lethal mutation?
A.
B.
C.
D.
E.
3.
Pro → Gly
Lys →Gly
Gly →Ala near the N-terminus
Gly →Asp near the C-terminus
Lys →Arg
The repeating secondary structures as found in ß-strands, ß-turns, and α-helices are
primarily stabilized by:
A.
B.
C.
D.
E.
4.
Stabilize the oxy form
Enhance O2 delivery to peripheral tissues
Destabilize the deoxy form
Oxidize Fe2+
Sterically block the O2 binding sites
Hydrogen bonds
Disulfide bonds
Hydrophobic interactions
Van der Waals interactions
Ionic interactions
If the nucleic acids were isolated and separated from cultured skin fibroblasts, where
would inosine most likely be located?
A.
B.
C.
D.
E.
DNA
Intron region of hnRNA
mature mRNA
tRNA
rRNA
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
1
5.
Which of the enzymes listed below possesses the following properties: recognizes the
promoter within the structural gene, catalyzes the polymerization of a small nucleic acid
that later on undergoes extensive base modifications, and is insensitive to rifampicin but
sensitive to high concentrations of alpha-amanitin.
A.
B.
C.
D.
E.
6.
As part of a summer research project, you are given the task of isolating and purifying an
enzyme from porcine kidneys. Which of the following separation techniques would most
likely yield the purest active enzyme in a single step?
A.
B.
C.
D.
E.
7.
Eukaryotic RNA polymerase I
Eukaryotic RNA polymerase II
Eukaryotic RNA polymerase III
Prokaryotic RNA polymerase
Viral reverse transcriptase
Affinity chromatography using a bound competitive inhibitor
SDS-polyacrylamide gel electrophresis
Ion-exchange chromatography
Differential centrifugation
Size-exclusion chromatography
Complete endonucleolytic digestion of sequences connecting two tandem nucleosomes
would produce DNA fragments of size:
A.
B.
C.
D.
E.
60 by
140 by
200 by
260 by
340 by
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
2
8.
Many antibiotics are inhibitors of protein synthesis. Which of the following correctly
matches the antibiotic with the mechanism by which it inhibits protein synthesis?
A.
B.
C.
D.
E.
9.
Which of the following is COMMON to myosin of smooth and striated muscle as well as
nonmuscle myosin I.
A.
B.
C.
D.
E.
10.
They are regulated by phosphorylation of light chains
They have movable lever arms
They attach to actin filaments that have troponin and tropomyosin
They have a coiled-coil tail
They form bipolar thick filaments
All of the following are true about all immunoglobulins, EXCEPT:
A.
B.
C.
D.
E.
11.
Chloramphenicol - prevents translocation
Erythromycin - prevents formation of the initiation complex
Puromycin - causes premature polypeptide chain termination
Streptomycin - inhibits binding of aminoacyl-tRNA to the A site
Tetracycline - inhibits peptidyltransferase
Contain multiple polypeptide chains
Contain disulfide bonds
Recognize antigens
Are synthesized by B cells
Contain a hydrophobic, membrane-bound domain
Antibody may be used as a probe to screen which of the following gene libraries for
identifying a clone carrying the gene of interest
A.
B.
C.
D.
A genomic library in lamda phage
A genomic library in cosmid
A genomic library in bacterial artificial chromosome
A cDNA library in expression plasmid
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
3
12.
Which of the following statements about heme and hemoglobin structure is/are
CORRECT:
1.
Intersubunit ionic bonds play a critical role in cooperative oxygen binding
2.
Binding of the heme to hemoglobin subunits relies on hydrophobic and
ionic interactions
3.
The iron of free heme has two unoccupied coordination positions
4.
The proximal 1Iis (F8) in both the alpha and beta chains participate in
coordination of the heme iron
A.
B.
C.
D.
E.
13.
Xeroderma pigmentosum arises due to persistence of:
A.
B.
C.
D.
E.
14.
1, 2 and 3 only
1 and 3 only
2 and 4 only
4 only
All four
Chemical indirect mutagenesis
Acridine intercalation
Inosine incorporation
Cytosine deamination
Thymidine dimers
A point mutation occurs in the gene for the leader peptide of the tryptophan operon of E.
coli causing one of the two codons for Trp to be changed to Phe. Which of the following
is the most likely outcome of this mutation?
A.
B.
C.
D.
E.
The resultant leader peptide becomes an inhibitor of RNA polymerase
The leader peptide acts as a corepressor yielding a repressor-corepressor complex
that prevents transcription
Transcription and translation of enzymes involved in the synthesis of Trp increase
The mutation results in a decreased ability to synthesize Trp when cellular levels
of Trp are low
The leader peptide inhibits the formation of Trp-mRNAtrp
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
4
15.
The synthesis of proteins requires the expenditure of energy in the form of high energy
phosphate bonds (ATP or GTP). Which of the following steps in the translation process
does not involve the cleavage of a high energy phosphate bond?
A.
B.
C.
D.
E.
16.
Which of the following statements is in agreement with the statement "The genetic code
is degenerate, but not ambiguous"?
A.
B.
C.
D.
E.
17.
Formation of aminoacyl tRNAs
Formation of the complete initiation complex
Bringing an aminoacyl tRNA to the A site
Formation of the elongated peptidyl tRNA
Moving the peptidyl tRNA from the A site to the P site
Many of the tRNAs carry more than one amino acid
All triplet codons have at least one uracil
Many of the amino acids are specified by more than one codon
There are 64 aminoacyl tRNAs
Some triplet codons are made up of repeating purines or pyrimidines
Which of the following is FALSE with respect to enzyme catalysis?
A.
B.
C.
D.
E.
Zero order reactions are independent of the substrate concentration
The Michaelis constant, KM, is a measure of substrate affinity
The initial rate of product formation, Vi, depends on enzyme and substrate
concentration
Noncompetitive inhibitors alter both Vmax and KM
The Hill coefficient is a measure of cooperativity
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
5
18.
Which of the following statements about vertebrate striated muscle is/are CORRECT:
1.
2.
3.
4.
A.
B.
C.
D.
E.
19.
1, 2 and 3 only
1 and 3 only
2 and 4 only
4 only
All four
An RNA fragment containing an adenylate residue linked to three nucleotides by
phosphodiester bonds likely resulted from which of the following processes:
A.
B.
C.
D.
E.
20.
ATP binds at the P loop region of myosin
A conformational change in myosin involving the relay helix immediately
follows ATP hydrolysis
Troponin C is the regulatory calcium-binding protein of the thin filament
Myosin head groups in relaxed muscle is bound to ADP, Pi, and actin
Splicing of Pre-mRNA
Polyadenylation
Processing of rRNA
Intron removal from pre-tRNA
5'-capping
Which amino acid residue would be least frequently found on surfaces of globular
proteins in aqueous solution?
A. Glutamate
B. Serine
C. Valine
D. Glutamine
E. Arginine
21.
The only RNA molecules that do not require post-transcriptional processing are the:
A.
B.
C.
D.
E.
Euka.ryotic rRNAs
Eukaryotic tRNAs
Prokaryotic rRNAs
Prokaryotic tRNAs
Prokaryotic mRNAs
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
6
22.
All of the following are TRUE statements about regulation of the expression of
eukaryotic genes EXCEPT:
A.
B.
C.
D.
23.
The antibiotic, ciprofloxacin, is an inhibitor of:
A.
B.
C.
D.
E.
24.
Sliding clamp
Helicase
DNA ligase
Primase
Topoisomerase
The increased metabolic activity that occurs in muscle tissue during exercise causes
hemoglobin to release more oxygen to the tissue for all of the following reasons
EXCEPT:
A.
B.
C.
D.
25.
Alternate splicing of tropomyosin gene transcripts can generate a family of tissuespecific proteins
In intestinal cells, the apoprotein B mRNA is modified creating a protein of
smaller size than its liver counterpart
During the production of antibodies, lymphocytes produce shorter transcripts by
using different cleavage and polyadenylation sites.
The iron response element (IRE) in the 5' untranslated region of ferritin binds a
specific protein that induces translation
Muscle produces higher levels of H+
Muscle produces higher levels of CO2
The partial pressure of oxygen in the muscle is reduced
BPG dissociates from hemoglobin
Which of the following enzyme-inhibitor interactions would yield Lineweaver-Burk plots
that had identical intercepts on the 1/Vi axis for the enzyme with and without inhibitor?
A.
B.
C.
D.
Inhibition of dihydrofolate reductase by the anticancer drug methotrexate
Inhibition of bacterial transpeptidase by penicillin
Inhibition of acetylcholinesterase by diisopropylfluorophosphate
Heterotropic allosteric inhibition of isocitrate dehydrogenase by ATP
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
7
26.
Allosteric regulatory enzymes:
A.
B.
C.
D.
E.
27.
All of the following statements accurately describe structural characteristics of collagen
EXCEPT:
A.
B.
C.
D.
E.
28.
Tropocollagen has a rod-shaped structure formed from three helical polypeptides
Each collagen a-chain is stabilized by intrachain H-bonds
The amino acid glycine is present in every third position in the collagen a-chain
Sugar residues are bound to collagen through hydroxylysine residues
Procollagen contains N- and C-terminal globular regions
The Bohr effect involves the side chain of histidine 146 in the beta chain of hemoglobin.
Consider a mutation in which histidine 146 is converted to lysine. If the mutation is not
lethal, which of the following molecular or physiological phenotypes would most likely
be observed?
A.
B.
C.
D.
E.
29.
Possess more than one subunit
Are always inhibited by their end product
Obey the enzyme kinetics of the Michaelis-Menten equation
Have a single binding site for their substrates
Remain in their initial conformation
A loss of cooperative oxygen binding to the mutated hemoglobin
An increase in the pH of peripheral tissues relative to normal levels
Polymerization of the mutated deoxyhemoglobin
An overall decrease in the affinity of the mutated hemoglobin for oxygen
Enhanced oxidation of Fe2+ to Fe3+
Which enzyme has an integral RNA component that acts as a template for DNA
synthesis?
A.
B.
C.
D.
E.
Telomerase
RNaseP
Peptidyl transferase
Nucleotidyl transferase
Reverse transcriptase
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
8
30.
Which of the following is FALSE regarding eukaryotic transcription?
A.
B.
C.
D.
31.
The backbones of DNA and RNA are formed by:
A.
B.
C.
D.
E.
32.
3'-to-5' phosphodiester bond
2' to 3' phosphodiester bond
Thymidine dimers
ß-glycosidic linkage
Nucleoside triphosphate bonds
Certain locations (loci) in the human genome are termed hypervariable loci and are
characterized by the presence of sequences that are repeated in tandem a variable number
of times; i.e., they contain a variable number of tandem repeats (VNTRs). What is the
chance that two siblings will be indistinguishable based on genetic testing for
hypervariability at one particular VNTR locus?
A.
B.
C.
D.
E.
33.
Histone SLeacetylation correlates with gene inactivity
Tamoxifen binding to the estrogen receptor prevents binding of the coactivator
TFIID binds the TATA box element upstream of promoters and recruits TFIIA
The proteolysis of the SREBP occurs in response to high levels of cholesterol
25%
33%
50%
75%
100%
A mutation in the lac repressor protein eliminates its binding to the lac operator. The
mutant strain displays:
A.
B.
C.
D.
E.
An inability to express the lactose operon-encoded genes under any circumstances
An inability to express the lactose operon-encoded genes unless lactose is present
and glucose is absent
The same level of expression of the lactose operon-encoded genes under all
circumstances
The highest level of expression of the lactose operon-encoded genes only when
glucose is absent whether or not lactose is present
The highest level of expression of the lactose operon-encoded genes only when
glucose is absent and lactose is present
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
9
34.
A homeless man presents to the emergency room with sore and bleeding gums and states
that he has recently lost several teeth. A dietary history indicates that he eats very little
fruit or vegetables, mostly fast food. You diagnose a case of scurvy, which in large part is
due to defective collagen synthesis. Which of the following steps in the biosynthesis of
collagen is directly affected by this dietary insufficiency?
A.
B.
C.
D.
E.
35.
The secretion of tropocollagen into the extracellular matrix
The formation of disulfide bonds that initiates tropocollagen formation
The intracellular hydroxylation of proline and lysine residues
The formation of collagen fibrils
The extracellular oxidation of lysine residues
Enzymes catalyze reactions and thus accelerate the rates of the reactions they catalyze by
utilizing a number of different catalytic strategies. Which of the following catalytic
strategies is/are utilized by the proteolytic enzyme chymotrypsin?
1.
2.
3.
4.
A.
B.
C.
D.
E.
36.
Formation of a covalent enzyme-substrate intermediate
Strain and distortion of the substrate
General acid-base catalysis
Stabilization of charge using a metal ion
1, 2 and 3 only
1 and 3 only
2 and 4 only
4 only
All four
Sickle cell anemia is associated with a restriction fragment polymorphism because
A.
B.
C.
D.
E.
A single nucleotide change results in loss of an Mst II sight in the beta globin
gene
The amino acid substitution results in a change in electrophoretic mobility of the
protein
The mutation is associated with a three base pair deletion
The mutation is associated with a change in the number of triplet repeats
associated with the beta globin gene
There is an expansion in the number of triplet repeats associated with the beta
globin gene
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
10
37.
The term secondary structure of proteins refers to:
1.
2.
3.
4.
A.
B.
C.
D.
E.
38.
If only 1, 2, and 3 are correct
If only 1 and 3 are correct
If only 2 and 4 are correct
If only 4 is correct
If all are correct
Amplification of DNA by means of polymerase chain reaction requires:
A.
B.
C.
D.
E.
39.
Alpha helix
Overall conformation
Beta pleated sheet
Subunit interactions
Reverse transcriptase, heat-stable DNA polymerase' and two primers
DNA ligase, heat-stable DNA polymerase and two primers
Repeated cycles of annealing, extension, denaturation and re-annealing
At lease two molecules of DNA as a starting template
Restriction enzymes
The heart (H) and skeletal muscle (M) isoforms of an enzyme differ in primary sequence
at two positions. The H-form has glutamate and lysine whereas the M-form has glutamine
and arginine. If heart damage can be assessed by measuring the ratios of the H and M
isoforms released in blood, which of the following would most likely be used to
determine if a patient had suffered a myocardial infarction (heart attack)?
A.
B.
C.
D.
E.
Affinity chromatography using a bound competitive inhibitor
Enzyme activity analysis
Isoelectric focusing
Size-exclusion chromatography
SDS-polyacrylamide gel electrophoresis
Medical School Biochemistry - Fall 2004
Block I Exam (Version 3- September 21, 2004)
FOR EACH OF THE FOLLOWING MULTIPLE CHOICE QUESTIONS CHOOSE THE
MOST APPROPRIATE ANSWER
11
40.
Which of the following analytical separation techniques can yield an estimate of the
molecular mass of a protein?
1.
2.
3.
4.
A.
B.
C.
D.
E.
41.
Matrix-assisted laser desorption ionization (MALDI) mass spectrometry
Isoelectric focusing
SDS-polyacrylamide gel electrophoresis
Affinity chromatography
1, 2, and 3 only
1 and 3 only
2 and 4 only
4 only
all four
Many membrane-bound and secretory proteins are synthesized on the rough endoplasmic
reticulum (RER). Following are events in the synthesis, of a secretory protein:
1.
2.
3.
4.
5.
Docking of the ribosome-mRNA complex to the RER
Translation of the signal sequence in the cytosol
Removal of the signal sequence by a signal peptidase
Binding of the signal recognition particle to the signal sequence.
Release of completed protein into the lumen of the RER.
Which of the following arranges the events in the correct sequence?
A.
B.
C.
D.
E.
42.
1→2→3→4→5
2→4→1→3→5
2→1→4→5→3
1→3→4→3→5
2 → 4 → 1 → 5→ 3
Cysteine side chains are capable of forming:
1.
2.
3.
4.
A.
B.
C.
D.
E.
Salt bridges
Disulfide bonds
Double bonds
Coordinate bonds with metals
1, 2 and 3 only
l and 3 only
2 and 4 only
4 only
All four
12
Answers
1. B
2. D
3. A
4. D
5. C
6. A
7. B
8. C
9. B
10. E
11. D
12. E
13. E
14. D
15. D
16. C
17. D
18. B
19. A
20. C
21. E
22. D
23. E
24. D
25. A
26. A
27. B
28. D
29. A
30. D
31. A
32. A
33. D
34. C
35. B
36. A
37. B
38. C
39. C
40. B
41. B
42. C
43. C
13