AAMC MCAT Practice Exam 1 Questions and Answers 2023

AAMC MCAT Practice Exam 1 Questions and Answers 2023 In the chromatography of the reaction mixture, water absorbed on cellulose functioned as the stationary phase. What was the principal factor determining the migration of individual components in the sample? A) Hydrogen bonding B) Solute concentration C) Stationary phase concentration D) Thickness of paper A) Hydrogen bonding The answer to this question is A because the relative amount of hydrogen bonding to the stationary phase will determine the relative rate of migration of the various components in the sample. What assumption is being made if scientists conclude that aspartic acid was formed by the prebiological synthesis in the passage? A) Aspartic acid is unstable at temperatures below 150 degrees C. B) All of the malic acid underwent the dehydration reaction to form fumaric/maleic acid. C) Compound A and cyanide were available on primitive Earth. D) The reaction between ammonia and fumaric acid was catalyzed by the presence of water. C) Compound A and cyanide were available on primitive Earth. he answer to this question is C since, in order for the experimental reaction sequence to be relevant to the primordial formation of aspartic acid, the starting materials used (Compound A and cyanide) are assumed to have been available. According to the developed chromatography plate shown below, what is the approximate Rf value of aspartic acid? aspartic acid = 2 solvent front = 10 A) 0.20 B) 0.50 C) 5 D) 10 The answer to this question is A (0.20) because Rf is the ratio of the distance travelled by the analyte relative to the solvent front during a chromatographic separation. Aspartic acid travelled two units, while the solvent front travelled ten units, giving an Rf of 2/10 = 0.20 for aspartic acid. Which of the following statements does NOT correctly describe the dehydration of malic acid to fumaric acid and maleic acid? A) The reaction occurs most readily with tertiary alcohols. B) The reaction involves the loss of a water molecule. C) The reaction has a carbocation intermediate. D) The reaction is stereospecific. D) The reaction is stereospecific. The answer to this question is D because the fact that both fumaric and maleic acid are produced means that the dehydration of malic acid is NOT stereospecific. What type of functional group is formed when aspartic acid reacts with another amino acid to form a peptide bond? A) An amine group B) An aldehyde group C) An amide group D) A carboxyl group C) An amide group The answer to this question is C because the functional group that forms during peptide bond formation is known as an amide group. If 2-pentanol replaces 1-pentanol in the reaction shown in Figure 3 (SN2), the rate of substitution is less because: A) the C-O bond in 2-pentanol is stronger than the C-O bond in 1-pentanol. B) there is a competing elimination reaction that slows the rate of substitution. C) there is more steric hindrance at the oxygen atom in 2-pentanol than in 1-pentanol, making protonation less likely. D) there is more steric hindrance at the 2-position of 2-pentanol than at the 1-position of 1-pentanol. D) there is more steric hindrance at the 2-position of 2-pentanol than at the 1-position of 1-pentanol. The answer to this question is D because the rate of substitution of protonated alcohols is subject to steric hindrance. This inhibits the ability of nucleophiles to collide with the reacting electrophilic center and slows the rate of reaction. If a solution containing the compounds shown in Figure 4, is injected into a gas-liquid chromatograph, the first peak observed in the gc trace is attributable to which compound? A) Methyl-2-butanol B) Methyl-2-butene C) Chloro-2-methylbutane D) Bromo-2-mehtylbutane B) Methyl-2-butene The answer to this question is B because 2-methyl-2-butene will exhibit the lowest molecular weight and also the weakest intermolecular forces of attraction. This substance will therefore migrate the fastest and be the first peak in the gas chromatograph (gc) trace. R vs. S stereochemistry* R = clockwise C = counter-clockwise Acetic acid and ethanol react to form an ester product as shown below. In determining which reactant loses the -OH group, which of the following isotopic substitutions would be most useful? A) Replace the acidic H of acetic acid with D B) Replace the alcoholic H of ethanol with D. C) Replace the carbonyl oxygen of acetic acid with O-18. D) Replace the hydroxyl oxygen of ethanol with O-18. D) Replace the hydroxyl oxygen of ethanol with O-18. The answer to this question is D because this experiment involves labeling a group which does not exchange with other groups present prior to reaction and will therefore give information about the true identity of the groups, which are exchanged during the reaction. A person whose eye has a lens-to-retina distance of 2.0 cm, can only clearly see objects that are closer than 1.0 m away. What is the strength S of the person's eye lens? (Note: Use the thin lens formula 1/O + 1/I = S) A) -50 D B) -10 D C) 51 D D) 55 D C) 51 D The answer to this question is C because the strength of the eye lens is equal to the inverse of the focal length of the eye lens. Its numerical value is given by (1 m)-1+(0.02 m)-1=1 D+50 D=51 D. Which statement correctly describes how enzymes affect chemical reactions? Stabilization of: A) the substrate changes the free energy of the reaction. B) the transition state changes the free energy of the reaction. C) the substrate changes the activation energy of the reaction. D) the transition state changes the activation energy of the reaction. D) the transition state changes the activation energy of the reaction. The answer is D because the stabilization of the transition state, not the substrate, provides binding energy that is used to lower the activation energy. Which of the following will decrease the percentage ionization of 1.0 M acetic acid, CH3CO2H(aq)?* A) Chlorinating the CH3 group B) Diluting the solution C) Adding concentrated HCl (aq) D) Adding a drop of basic indicator C) Adding concentrated HCl (aq) The answer to this question is C because HCl is a strong acid that will increase the amount of H+ in solution and thus decrease the percentage of CH3CO2H that ionizes. When the current in the micro-robot's circuit increases and the resistance of the circuit remains constant, the voltage of the circuit: A) decreases B) increases C) is constant D) is zero B) increases V = IR The answer to this question is B because according to Ohm's law, current is equal to voltage divided by resistance. If current increases and resistance is constant, then voltage increases as well. Knowing that the speed of light in the vitreous humor is 2.1 × 108 m/s, what is the index of refraction of the vitreous humor? (Note: The speed of light in a vacuum is 3.0 × 108 m/s.) A) 0.7 B) 1.4 C) 2.1 D) 3.0 B) 1.4 n = c/v The answer to this question is B because the index of refraction of a medium is equal to the ratio of the speed of light in vacuum to the speed of light in the medium, thus it is equal to (3.0 x 108 m/s)/(2.1 x 108 m/s) = 1.4. The intensity of the radiation emitted by the oxygen sensor is directly proportional to the: A) propagation speed of the radiation B) wavelength of the radiation C) polarization of photons emitted D) number of photons emitted D) number of photons emitted The answer to this question is D because the energy of electromagnetic radiation is directly proportional to the number of photons, and the intensity of electromagnetic radiation is defined as energy emitted per unit time. Thus, intensity is directly proportional to the number of photons emitted. What is the energy of the photons emitted by the LED at a frequency of 610 THz? (Note: h = 6.6 × 10-34 J·s) A) 9.2 × 10-12 J B) 1.6 × 10-16 J C) 1.1 × 10-18 J D) 4.0 × 10-19 J D) 4.0 × 10-19 J The answer to this question is D because the energy of a photon of frequency 610 THz is equal to 6.6 x 10-34 J•s x 610 x 1012 Hz = 4 x 10-19 J. What percentage of standard atmospheric pressure is the pulse pressure of a healthy adult? The maximum and minimum blood pressures of a healthy adult are about Ps = 120 mmHg and Pd = 75 mmHg. Pp = Ps-Pd A) 10% B) 6% C) 2% D) 1% B) 6% The answer to this question is B because the pulse pressure in a healthy adult is (120 − 75) mmHg = 45 mmHg, and so the percentage is 45 mmHg/760 mmHg = 6%. What fraction of a O-15 sample decays in 10 min? "The location of internal organs where changes in the calcium content occur can be found by placing positron-emitting isotopes such as O-15 (with a half-life = 2 min) into the patient's bloodstream) A) 1/8 B) 9/16 C) 3/4 D) 31/32 D) 31/32 The answer to this question is D because the half-life of 15O is 2 minutes; thus, 10 minutes = 5 half-lives. Therefore, only (1/2)5 = 1/32 of the sample will be left after 10 minutes, while 31/32 of the sample will decay. Compared to micellular Compound 1, Compound 2 is structurally more rigid as a result of what type of interaction? A) Intermolecular hydrogen bonding B) Intermolecular covalent bonding C) Intramolecular hydrogen bonding D) Intramolecular covalent bonding B) Intermolecular covalent bonding The answer to this question is B. It can be reasoned that the interaction described is intermolecular in nature, since multiple molecules of micellular Compound 1 come together to form Compound 2, which is a solid. Multiple pieces of information point to the fact that the interaction is disulfide bond formation, including the fact that an oxidant causes the formation of Compound 2, which can be reversed by the addition of a reducing agent. Which amino acid residues were incorporated into Compound 1 to promote the adhesion of cells on the scaffold surfaces? A) Arg and Gly B) Cys and Gly C) Cys and Asp D) Asp and Arg D) Asp and Arg The answer to this question is D. The residues that were engineered into the peptide for cell adhesion are arginine and aspartate as can be reasoned based on the structure of the peptide provided, and the description of the roles of the various residues provided in the passage. Which amino acid was incorporated into Compound 1 as a future site of covalent attachment to HA prior to mineralization? A) Ser B) Ala C) Tyr D) Thr A) Ser The answer to this question is A because serine is the residue that was phosphorylated, and phosphorylation enabled the protein to be subsequently attached to hydroxyapatite (HA). Compound 1 was designed to exhibit pH-dependent self-assembly. What feature(s) of the molecule is(are) responsible for the pH dependence of aggregation (Equation 1)? A) Thiol side chains that can hydrogen bond B) Long alkyl chains that exhibit predominantly London forces C) Side chains whose net charge responds to pH D) Covalent linkages that reversibly hydrolyze C) Side chains whose net charge responds to pH The answer to this question is C because the molecule contains mainly acidic side chains that were deprotonated and negatively charged at high pH. This inhibited aggregation due to electrostatic principles. At low pH these groups are neutral and this allowed aggregation. Why is the velocity of blood flow slower in capillaries than in arteries? A) Capillary walls are more elastic than arterial walls. B) Capillaries have less resistance to blood flow than arteries. C) The total cross-sectional area of capillaries exceeds that of arteries. D) Blood pressure is higher in the capillaries than in arteries. C) The total cross-sectional area of capillaries exceeds that of arteries. A1v1 = A2v2 The answer to this question is C because the high number of capillaries in the body means that the total cross-sectional area of these vessels is larger than any other vessel type in the circulatory system. This causes the velocity of the blood to decrease. Which of the following types of orbitals of the central atom is involved in bonding in octahedral compounds? A) sp B) sp3 C) p D) d2 sp3 D) d2 sp3 The answer to this question is D because octahedral compounds have six σ bonds and no lone pairs. According to valence bond theory, the central atom requires the hybridization of six atomic orbitals, d2sp3. The term "ideal gas" refers to a gas for which certain assumptions have been made. Which of the following is such an assumption? A) The law PV = nRT^2 is strictly obeyed. B) Intermolecular forces are infinitely large. C) Individual molecular volume and intermolecular forces are negligible. D) One gram-mole occupies a volume of 22.4 L at 25 degrees C and one atmosphere pressure. C) Individual molecular volume and intermolecular forces are negligible. The answer to this question is C since a property of an "ideal" gas is that it is composed of particles that have negligible volume and do not exert intermolecular forces. The production of a variety of opsins functions to: "Additional opsin based receptors are expressed in specialized cone cells" A) increase sensitivity to low light B) enable the detection of different colors C) ensure fast recovery of 11-cis retinal after exposure D) increase refractive index of the eye lens B) enable the detection of different colors The answer to this question is B. The wavelength of light absorbed by a molecule depends on its structure, and so the production of a variety of structurally related opsins functions to enable the detection of different colors. The environment of the retinal binding site is most likely: "Rhodopsin is composed of opsin, a family of seven helix transmembrane proteins, and a covalently attached coenzyme, retinal." A) hydrophilic B) positively charged C) negatively charged D) hydrophobic D) hydrophobic The answer to this question is D because retinal is composed of mainly carbon and hydrogen, making it largely hydrophobic. The source of the phosphate groups that are added to rhodopsin is: "Wild-type or variant rhodopsin was reconstituted with 11-cis-retinal and phosphorylated by rhodopsin kinase in the presence of ATP before examining arrestin binding" A) arrestin B) rhodopsin kinase C) ATP D) all-trans-retinol C) ATP The answer is C because the requirement of ATP for kinase activity implies the phosphate groups come from ATP. What are the hybridization states of the carbon atoms involved in the conversion of trans to cis retinal? A) sp B) sp2 C) sp3 D) sp3d B) sp2 he answer to this question is B because the reacting carbon atoms are both central to AX3 systems with 3 bonded atoms and no lone pairs. The preferred geometry for such a system is trigonal planar and the hybridization scheme that facilitates this geometry is sp2. Which reaction is catalyzed by LipA? A) ATP hydrolysis B) Peptide bond cleavage C) Hydrolysis of triacylglycerides D) Transfer of carboxyl groups C) Hydrolysis of triacylglycerides The answer is C because the fact that LipA is a lipase, which means it must hydrolyze fatty acids. Compared to the wild-type LipA, what is the change in net charge in variant XI at pH 7? R33G K112D M134D Y139C I157M A) +4 B) +3 C) -3 D) -4 D) -4 The answer is D because the amino acid substitutions replace amino acids with charges of +1, +1, 0, 0, and 0 with ones that have charges of 0, −1, −1, 0, and 0 so the net charge goes from +2 to −2. The data in Figure 1 show that: A) the unfolding of LipA proteins is a non-reversible process. B) exposure to high temperature eliminates any variant protein activity. C) variation in the flexible regions of LipA decreases the temperature sensitivity of activity. D) wild-type LipA loses all activity when first heated to 50°C. C) variation in the flexible regions of LipA decreases the temperature sensitivity of activity. The answer is C because the data show that variation of the flexible regions results in less temperature sensitivity of activity. Activity returns even when variants are exposed to high temperature. By what factor is the proton concentration increased in the experiments shown in Figure 1B from those shown in Figure 1A? Figure 1A - pH 7 Figure 1B - pH 4 A) 2 B) 10 C) 200 D) 1000 D) 1000 The answer to this question is D because the pH scale is logarithmic (pH = −log([H+]). A difference of 3 pH units corresponds to a 103 = 1000-fold difference in proton concentrations. Which type of bond is formed by glycogen synthase upon release of UDP? A) α-1,4-Glycosidic bond B) α-1,6-Glycosidic bond C) β-1,4-Glycosidic bond D) β-1,6-Glycosidic bond A) α-1,4-Glycosidic bond The answer is A because the bond that is formed by glycogen synthase is the main chain linkage of glycogen, which is an α-1,4-glycosidic bond. UDP release means that only glucose was added. In addition to glucose, what other monosaccharide is part of the UDP-glucose structure? A) Xylose B) Fructose C) Ribose D) Arabinose C) Ribose The answer is C because UDP contains uridine, which is a nucleic acid used in RNA. The structure of RNA contains ribose. Addition of laforin to the reaction mixtures used to generate the data in Figure 2 will result in: "LBs contain a much larger amount of covalently-linked phosphate compared to normal glycogen." A) a decrease in the intensity of the band representing WT without glucosidase when visualized with 14C decay. B) an increase in the intensity of the band representing WT without glucosidase when visualized with 14C decay. C) a decrease in the intensity of the band representing WT without glucosidase when visualized with 32P decay. D) an increase in the intensity of the band representing WT without glucosidase when visualized with 32P decay. C) a decrease in the intensity of the band representing WT without glucosidase when visualized with 32P decay. The answer is C because laforin is an enzyme that removes phosphate from glycogen. Presumably, the removal of phosphate prior to gel electrophoresis will result in a smaller band corresponding to 32P incorporation.