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AAMC MCAT PRACTICE EXAM 2
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AAMC MCAT PRACTICE EXAM 2
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AAMC MCAT PRACTICE EXAM 2C/P: What expression gives the amount of light energy (in J per photon) that is
converted to other forms between the fluorescence excitation and emission events?
"intensity of fluorescence emission at 440 nm excitation at 360 nm) was monitored for
20 minutes"
A) (6.62 × 10-34) × (3.0 × 108)
B) (6.62 × 10-34) × (3.0 × 108) × (360 × 10-9)
C) (6.62 × 10-34) × (3.0 × 108) × [1 / (360 × 10-9) - 1 / (440 × 10-9)]
D) (6.62 × 10-34) × (3.0 × 108) / (440 × 10-9) - Answers- C) (6.62 × 10-34) × (3.0 ×
108) × [1 / (360 × 10-9) - 1 / (440 × 10-9)]
The answer to this question is C because the equation of interest is E = hf = hc/λ,
where h = 6.62 × 10 −34 J ∙ s and c = 3 × 10 8 m/s. Excitation occurs at λe = 360 nm,
but fluorescence is observed at λf = 440 nm. This implies that an energy of E = (6.62 ×
10 −34) × (3 × 10 8) × [1 / (360 × 10 −9) − 1 / (440 × 10 −9)] J per photon is converted
to other forms between the excitation and fluorescence events.
C/P: Compared to the concentration of the proteasome, the concentration of the
substrate is larger by what factor?
"purified rabbit proteasome (2 nM) was incubated in the presence of porphyrin...the
reaction was initiated by addition of the peptide (100 uM)"
A) 5 × 101
B) 5 × 102
C) 5 × 103
D) 5 × 104 - Answers- D) 5 × 104
The answer to this question is D. The proteasome was present at a concentration of 2 ×
10-9 M, while the substrate was present at 100 × 10-6 M. The ratio of these two
numbers is 5 × 104.
sp2 hybridized - Answers- possess exactly one doubly bonded atom
C/P: The concentration of enzyme for each experiment was 5.0 μM. What is kcat for the
reaction at pH 4.5 with NO chloride added when Compound 3 is the substrate?
Rate of reaction = 125 nM/s
A) 2.5 × 10-2 s-1
B) 1.3 × 102 s-1
C) 5.3 × 103 s-1
,D) 7.0 × 105 s-1 - Answers- A) 2.5 × 10-2 s-1
The answer to this question is A. The fact that the rate of product formation did not vary
over time for the first 5 minutes implies that the enzyme was saturated with substrate.
Under these conditions, kcat = Vmax/[E] = (125 nM/s)/5.0 μM = 2.5 × 10-2 s-1.
kcat, Vmax, [E] - Answers- kcat = Vmax/[E]
C/P: Absorption of ultraviolet light by organic molecules always results in what process?
A) Bond breaking
B) Excitation of bound electrons
C) Vibration of atoms in polar bonds
D) Ejection of bound electrons - Answers- B) Excitation of bound electrons
The answer to this question is B. The absorption of ultraviolet light by organic
molecules always results in electronic excitation. Bond breaking can subsequently
result, as can ionization or bond vibration, but none of these processes are guaranteed
to result from the absorption of ultraviolet light.
C/P: Four organic compounds: 2-butanone, n-pentane, propanoic acid, and n-butanol,
present as a mixture, are separated by column chromatography using silica gel with
benzene as the eluent. What is the expected order of elution of these four organic
compounds from first to last?
A) n-Pentane → 2-butanone → n-butanol → propanoic acid
B) n-Pentane → n-butanol → 2-butanone → propanoic acid
C) Propanoic acid → n-butanol → 2-butanone → n-pentane
D) Propanoic acid → 2-butanone → n-butanol → n-pentane - Answers- A) n-Pentane
→ 2-butanone → n-butanol → propanoic acid
The answer to this question is A. The four compounds have comparable molecular
weights, so the order of elution will depend on the polarity of the molecule. Since silica
gel serves as the stationary phase for the experiment, increasing the polarity of the
eluting molecule will increase its affinity for the stationary phase and increase the
elution time (decreased Rf).
C/P: The half-life of a radioactive material is:
A) half the time it takes for all of the radioactive nuclei to decay into radioactive nuclei.
B) half the time it takes for all of the radioactive nuclei to decay into their daughter
nuclei.
C) the time it takes for half of all the radioactive nuclei to decay into radioactive nuclei.
D) the time it takes for half of all the radioactive nuclei to decay into their daughter
nuclei. - Answers- D) the time it takes for half of all the radioactive nuclei to decay into
their daughter nuclei.
,C/P: Which amino acid will contribute to the CD signal in the far UV region, but NOT the
near UV region, when part of a fully folded protein?
"Asymmetry resulting from tertiary structural features causes the largest increase in CD
signal intensity in the near UV region of peptides. The side chains of amino acid
residues absorb in this region.
The peptide bond absorbs in the far UV region (190-250 nm). The CD signals of these
bonds are dramatically impacted by their proximity to secondary structural elements."
A) Trp
B) Phe
C) Ala
D) Tyr - Answers- C) Ala
C/P: Based on the relative energy of the absorbed electromagnetic radiation, which
absorber, a peptide bond or an aromatic side chain, exhibits an electronic excited state
that is closer in energy to the ground state?
"Asymmetry resulting from tertiary structural features causes the largest increase in CD
signal intensity in the near UV region of peptides. The side chains of amino acid
residues absorb in this region.
The peptide bond absorbs in the far UV region (190-250 nm). The CD signals of these
bonds are dramatically impacted by their proximity to secondary structural elements."
A) An aromatic side chain; the absorbed photon energy is higher.
B) An aromatic side chain; the absorbed photon energy is lower.
C) A peptide bond; the absorbed photon energy is higher.
D) A peptide bond; the absorbed photon energy is lower. - Answers- B) An aromatic
side chain; the absorbed photon energy is lower.
The answer to this question is B because aromatic side chains absorb in the near UV
region of the electromagnetic spectrum, which has longer wavelengths, and hence
lower energy, than peptide bonds. Because the energy of the photon matches the
energy gap between the ground and the excited state, this implies that the aromatic side
chain has more closely spaced energy levels.
C/P: What is the net charge of sT-loop at pH 7.2?
"A synthetic peptide with the amino acid sequence KTFCGPEYLA was generated as a
mimic of the T-loop. This synthetic T-loop (sT-loop) was incubated with 32P-labeled ATP
, in the presence of PDK1 for different time periods at 37 ° C and pH 7.2, and the amount
of radioactivity incorporated into sT-loop was measured by detection of β- decay."
A) -2
B) -1
C) 0
D) +1 - Answers- C) 0
The answer to this question is C because at pH 7.2, the N-terminus will be positively
charged and the C-terminus will be negatively charged. In addition, the lysine side chain
will carry one positive charge and the glutamic acid side chain will carry one negative
charge.
C/P: In designing the experiment, the researchers used which type of P-32 labeled
ATP?
A) aP32-ATP
B) BP32-ATP
C) γP32-ATP
D) δP-32 ATP - Answers- D) δP-32 ATP
The answer to this question is D because the half-life of a radioactive material is defined
as the time it takes for half of all the radioactive nuclei to decay into their daughter
nuclei, which may or may not also be radioactive.
C/P: A person is sitting in a chair. Why must the person either lean forward or slide their
feet under the chair in order to stand up?
A) to increase the force required to stand up
B) to use the friction with the ground
C) to reduce the energy required to stand up
D) to keep the body in equilibrium while rising - Answers- D) to keep the body in
equilibrium while rising
The answer to this question is D because as the person is attempting to stand, the only
support comes from the feet on the ground. The person is in equilibrium only when the
center of mass is directly above their feet. Otherwise, if the person did not lean forward
or slide the feet under the chair, the person would fall backward due to the large torque
created by the combination of the weight of the body (applied at the person's center of
mass) and the distance along the horizontal between the center of mass and the
support point.
C/P: The side chain of tryptophan will give rise to the largest CD signal in the near UV
region when:
A) present as a free amino acid
B) part of an a-helix
C) part of a B-sheet
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