AAMC MCAT Practice Exam 2 fully solved 2023

AAMC MCAT Practice Exam 2 fully solved 2023C/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) - correct answer 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 - correct answer 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 - correct answer 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 - correct answer 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] - correct answer 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 - correct answer 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 - correct answer 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. - correct answer D) the time it takes for half of all the radioactive nuclei to decay into their daughter nuclei. 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 - correct answer 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 D) part of a fully folded protein - correct answer D) part of a fully folded protein The answer to this question is D because tryptophan has an aromatic side chain that will give rise to a significant CD signal in the near UV region if it is found in a fully folded protein. 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."