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SBPM SSN- Practice Questions for Exam #1
1. Which of the following statements is/are true about hemoglobin S, the variant of Hb most commonly
associated with sickle cell disease?
I. Relative to hemoglobin A, a charged surface amino acid has been replaced with a hydrophobic amino
acid.
II. In solution, it exhibits a higher P50 than hemoglobin A.
III. Has a tendency to polymerize upon O2 binding.
IV. Binds 2,3-DPG with lower affinity than hemoglobin A does.
A. I only
B. I and III
C. II and IV
D. I, II, III, and IV
2. Addition of a noncompetitive inhibitor to an enzyme that obeys Michaelis-Menten kinetics
A. will increase KM.
B. will decrease the y-intercept of the Lineweaver-Burk plot.
C. can be compensated for by adding a large excess of substrate.
D. none of the above
3. Which of the following promote(s) membrane fluidity?
A. Cis double bonds in lipid fatty acyl chains.
B. Cholesterol at high temperatures.
C. Long (as opposed to short) lipid fatty acyl chains.
D. A and C
4. Which of the following is NOT a stage in prophase of meiosis I in both sexes?
A. Zygotene
B. Diplotene
C. Dictyotene
D. Diakinesis
Bonus: What is the answer actually associated with?
5. 16% of a class of bored medical students have the ability to roll their tongues. Assume that tonguerolling is an autosomal recessive disor...um, trait. What percentage of the class is heterozygous for the
tongue rolling gene?
A. 84
B. 68
C. 24
D. 48
6. Which of the following is NOT a modifier of phenotypic expression?
A. Penetrance
B. Somatic mosaicism
C. Expressivity
D. Pleiotropy
Bonus: Define each of these.
7. Which of the following is a hallmark of unstable CAG (expanding) repeat diseases?
A. They are more severe as the repeat gets longer
B. They are typically musculoskeletal diseases
C. They are recessively inherited
D. They appear later in life as the repeat gets longer
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8. Which of the following scenarios would have the most immediate deleterious effect on gene
transcription of a cell surface protein in a yeast cell?
A. Removing all EF-Tu from the nucleus
B. Moving the enhancer region 100 bp further upstream from the promoter
C. Sucking out all RNA Polymerase III instantaneously
D. Inverting the promoter region
9. If you could peer into a yeast cell and watch it synthesize a functional gene product, which of the
following steps would you observe last?
A. Binding of the 40S subunit
B. Creation of a 2’-5’ phosphodiester bond
C. Formation of a lariat structure
D. Exporting RNA from nucleus
10. Which of the following is correct regarding adenylate cyclase?
A. Causes the formation of IP3 and DAG
B. Can alter gene expression in target cells
C. Is activated by the release of intracellular calcium
D. A and B are true
E. A, B and C are true
11. A fibroblast spontaneously loses its ability to produce kinetochores (but the genome is otherwise
undamaged). Upon receiving growth factors, it tries to divide. Which stage would you be most likely to
be see it “stuck” in?
A. Go
B. M-phase
C. G1
D. G2
12. Which stage of mitosis is most characterized by the shortening of kinetochore microtubules?
A. Prometaphase
B. Metaphase
C. Anaphase A
D. Anaphase B
E. Telophase
13. If a protein destined for import into the mitochondrial matrix becomes stuck in the intermembrane
space of the mitochondria, which of the following proteins is probably defective?
A. TOM
B. Hsp70
C. TIM
D. MtHsp60
14. Which of the following is true regarding glycogen synthesis?
A. It takes place on glycogenin
B. Glucose is added to the growing polymer as glucose-1-phosphate
C. It is stimulated by glucagon and inhibited by insulin
D. Glycogen synthase introduces branch points into the growing polymer
15. Which of the following cellular conditions would NOT stimulate ATP consumption?
A. High intracellular Na+
B. DNA translation
C. Glycogen synthesis
D. Folding/unfolding of proteins by heat shock proteins
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16. Which of the following is/are NOT a post-translational modification?
I. The incorporation of a signal that will target a peptide to the lysosome
II. The incorporation of a signal that will target a peptide to the nucleus
III. The incorporation of a signal that will cause a peptide to be an integral protein
IV. The incorporation of a signal that will target a peptide for export out of the cell
A. II only
B. I and IV
C. II and III
D. I and II
17. The lumen of the ER is "continuous" (continuous = something could go from one to the other without
crossing a membrane) with which of the following spaces:
I. The nucleolus
II. Outside of the cell
III. The lumen of the Golgi
IV . The perinuclear space
A. I and IV
B. III and IV
C. II and IV
D. II, III and IV
18. Which of the following statements is correct?
A. The -helix can be composed of more than one polypeptide chain
B. -sheets exist only in the antiparallel form
C. -bends often contain proline
D. Motifs are a type of secondary structure
19. Which of the following statements correctly characterizes the contribution of molecular forces in
determining protein structure?
A. Ionic bonds are the strongest type of intermolecular bonds, so they are
mostly responsible for determining protein structure.
B. Hydrophobic forces contribute significantly to protein structure.
C. Hydrogen bonding is important for secondary structure, but not for
tertiary or quaternary structure.
D. Van der Waals forces are strongest between two atoms that are far apart from one another.
20. One of the main functions of hepatocytes is detoxification. For this reason, which cell structure is
prominent?
A. Nucleolus
B. Golgi apparatus
C. Rough endoplasmic reticulum
D. Smooth endoplasmic reticulum
21. Why do mitochondria have two membranes?
A. To maintain a proton gradient
B. Because they originated as symbiotic prokaryotes
C. Mitochondria do not have two membranes
D. To prevent leakage of cytochrome C, which would result in activation of
the apoptotic cascade.
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22. All of the following statements regarding cytoskeletal structures are correct except
a. Microfilaments are found in abundance in cells requiring extra structural support, such as neurons.
b. Intermediate filaments provide tensile strength
c. Microtubules are hollow and thick, and serve as tracks for
intracellular transport.
d. Actin polymerization and depolymerization accounts for moment-to-moment
changes in cell shape.
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Answers:
1. A - Only statement I is true. While hemoglobin S does polymerize, it is the deoxygenated form that is
prone to undergo this process of nucleation and polymerization, so statement III is incorrect. When in
solution, however, hemoglobin S exhibits O2 binding characteristics that are essentially the same as
hemoglobin A, ruling out statement II. Its interactions with allosteric effectors also do not differ from
hemoglobin A, so statement IV is false; it is hemoglobin F that binds 2,3-DPG less strongly than
hemoglobin A.
2. D - Choices A and C are features of competitive inhibition. In noncompetitive inhibition, V max is less, so
the y-intercept of the Lineweaver-Burk plot, 1/Vmax, is in fact greater, making choice B incorrect. Note that
the enzyme will never be able to reach Vmax in the presence of a noncompetitive inhibitor, no matter how
much substrate is added.
3. A - Cis double bonds introduce kinks that cause the chains to pack together less well, so they are
easier to separate, promoting mobility. Cholesterol increases fluidity at low temperatures by preventing
phospholipids and glycolipids from packing too tightly, but at high temperatures the rigidity of the steroid
ring system actually keeps the membrane from becoming too fluid, so choice B is incorrect. Long fatty
acyl chains associate more strongly, not less (tend to be extended and pack better; van der Waals forces
increase with increasing molecular surface area), so choice C is also incorrect. Lipids with long, straight
(unsaturated) fatty acyl chains (like glycolipids, a.k.a. glycosphingolipids) can aggregate into domains of
higher order to form lipid rafts.
4. C - Dictyotene is associated with the pause in prophase I in oocytes after diplotene.
5. D - Use p+q = 1 and p2 + 2pq + q = 1 to solve for 2pq (heterozygotes). The answer is not pq (c)
because it's a binomial expansion; i.e., the homozygotes (p^2 and q^2) plus the heterozygotes (2pq from
the expansion) = 1, the entire population.
6. B - Somatic mosaicism is a non-classical pattern of single-gene inheritance. Penetrance is the number
of people with a particular genotype who are actually affected. Expressivity describes the degree of
expression of a phenotype. Pleitropy is when a single abnormal gene or gene pair produces diverse
phenotypic effects.
7. A - A hallmark of unstable expanding repeat diseases is that they are more severe and have an earlier
onset as the repeat gets longer. Therefore, choice A is correct and choice D is wrong. Choice B is wrong
because unstable CAG repeat diseases are all neurodegenerative diseases. Choice C is wrong because,
except for Kennedy disease, they are all dominantly inherited.
8. D - Moving the location of the enhancer or even inverting it would have little or no effect on gene
transcription. The EF-Tu cycle is critical in gene translation in prokaryotes (not yeast); not gene
transcription. Translation also occurs in the cytosol. RNA Pol III is necessary to transcribe RNA for
snRNA and scRNA; neither are critical for transcription. The position of the promoter is critical for the
binding of transcription factors and transcription.
9. A - While in the nucleus, a 5’ cap (5’-5’ P bond) and a Poly-A tail are added. Introns are spliced
through the formation of a lariat structure. The primary RNA is exported from the nucleus to the cytosol
where the small unit of the ribosome binds (40S) to initiate translation.
10. B - Adenylate cyclase causes the formation of cAMP. The inhibitory regulatory regions of PKA are
removed after the binding of 4 cAMP molecules, and PKA can translocate to the nucleus and activate
transcription factors such as CREB. IP3 and DAG are formed from the cleaved of PIP2 by PLC.
Intracellular calcium is important for activation of PLC and CAM dependent kinases, but adenylate
cyclase is activated directly by Gα-GTP through a G-protein coupled receptor.
11. B - A cell will not continue to anaphase of mitosis unless its chromosomes can properly align on the
metaphase plate. If a mutation occurs in a kinetochore, the spindles won’t be able to form properly. The
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cell will be stuck in the M-phase. A Go cell is quiescent and is not dividing. The G 1 checkpoint occurs
before S phase and the cell uses p53 to look for DNA damage. At the G 2 checkpoint, the cell senses
unreplicated DNA and looks for DNA damage.
12. C - In Anaphase A, the sister chromatids separate and begin to move towards each pole. This is
caused by a combination of kinetochore microtubule shortening and molecular motors. The
chromosomes first attach to microtubules in prometaphase and align at the metaphase plate in
metaphase. Anaphase B is characterized by the lengthening of polar microtubules to elongate the cell.
In telophase, the nuclear envelope of each daughter cell reassembles and the chromosomes
decondense.
13. C - TIM proteins facilitate the transport of proteins across the inner mitochondrial membrane. TOM
proteins mediate transport across the outer mitochondrial membrane. Hsp70's are cytosolic chaperonins
that bind to proteins destined for mitochondrial import and maintain them in a loosely folded conformation
suitable for import. MtHsp60 is a chaperonin that mediates the refolding of proteins after they have been
imported into the mitochondrial matrix.
14. A - In glycogen synthesis, glucose is added to the growing polymer as UDP glucose. Insulin
stimulates glycogen synthesis and glucagon inhibits it. Branching enzyme creates branch points in the
growing polymer by moving glucose residues to an internal site. Glycogen synthase elongates the
polymer by adding oligomers of glucose. Therefore, A is the only correct answer.
15. C - Na+/K+ Pump consume ATP. RNA’s are built with ATP’s and also the machinery requires an
input of energy, which is supplied by ATP. Heat Shock proteins (like Hsp 60 and Hsp 70) consume ATP.
Glycogen synthesis actually uses UTP.
16. C - The Nuclear Localization Sequence (II) and start transfer (III) sequence are both part of the
primary sequence of a polypeptide and are therefore incorporated during translation. Targeting to the
lysosome or for extracellular export require the addition of carbohydrate tags which are added post
translation in the Golgi apparatus
17. D - To send materials from the lumen of the ER to outside the cell or the lumen of the Golgi the cell
commonly uses vesicles with the SNARE protein system. Vesicle transport does not require crossing a
membrane. The perinuclear space is connected to the ER in many regions. The nucleolus on the other
hand is in the nucleus, which is contiguous with the cytosol via nuclear pores, which are essentially
cytoplasmic bridges. Since we can consider the nucleolus continuous with the cytosol and we know that
to get into the ER lumen, something has to cross a membrane (recall polypeptide translocation during
translation) we know that I is not correct.
18. C - Proline causes a "kink" in the polypeptide chain, so it is often where a strand of a -sheet turns to
begin the next strand. -helices, unlike -sheets, always involve the coiling of one polypeptide chain. sheets can be parallel or antiparallel. Motifs are elements of tertiary
structure.
19. B - Although hydrophobic forces are individually weak, they add up to become the most significant
force in forming an energetically favorable configuration. Ionic bonds, though strong, are much fewer.
Hydrogen bonding plays a role in secondary, tertiary, and quaternary structure.
Van der Waals forces become negligible at long distances.
20. D - Smooth endoplasmic reticulum is responsible for detoxification. The nucleolus, golgi, and rough
endoplasmic reticulum would be prominent in case of increased protein production.
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21. B - Aerobic prokaryotes were taken up by eukaryotes to become mitochondria via endocytosis. The
plasma membrane that wrapped around the prokaryote was retained as the outer mitochondrial
membrane. Only one membrane is necessary to prevent leakage (remember lysosomes); in fact, the
outer membrane of mitochondria is quite leaky.
22. A - Microfilaments, made of actin, are mostly responsible for movement and changes in cell shape.
Cells requiring extra structural support have an abundance of intermediate filaments.