Princeton MCAT Exam #2 Test Prep Actual Questions And Correct Detailed Answers

What single change to the experimental system would reduce the electric field strength necessary to maintain the oil drop in static equilibrium? - correct answer Decreasing the mass of the drop -When the oil drop (with charge -q) is in static eqbm, the electric force it feels, qE upward, is balanced by the gravitational force, mg downward. Thus, qE = mg, so E = mg / q. Don't be confused by the electric field strength in a capacitor, E = V / d. Which of the following equations gives the voltage V necessary to maintain an oil droplet of mass m and charge -q suspended in the region between Plates A and B, which are separated by a distance d? - correct answer V = mgd / q -The voltage V & the electric field strength E, between Plates A and B are related by the equation V = Ed, where d is the distance between the plates. The oil drop is suspended in the region between the plates when qE = mg or in terms of V, when q(V / d) = mg. Solving this last equation for V gives V = mgd / q. Which one of the following graphs best illustrates the relationship between a, an oil drop's acceleration perpendicular to the plates, and E, the strength of the electric field between the plates? - correct answer The net force on an oil drop (charge -q) between Plates A and B is the difference between the electric force and the gravitational force: Fnet = qE - mg. Since Fnet = ma, the acceleration of the oil drop is given by the equation a = (q/m)E - g. This is an equation of the form "y = mx + b," whose graph is a straight linear line with positive slope rising upwards What best explains the variation among the values of the floating voltage for the different droplets? - correct answer The charge of the droplets differs because the amount of ionization due to the x-rays is random -there is no way to control the exact number of excess electrons in the ionized air that will cling to a falling oil droplet, but the net charge must be a whole number multiple of the elementary charge. What impact do the results shown in Figure 1 have on the hypothesis that leptin resistance secondary to obesity reduces all effects of leptin? - correct answer Weakens the hypothesis due to the increase in neural activity with injection of leptin in obese mice -given the dramatic increase in nerve activity with increasing leptin dosage, leptin does have an impact on RSNA. Thus leptin resistance secondary to obesity does NOT reduce ALL effects of leptin weakening q-stem hypothesis A researcher proposed to block the leptin receptor in order to treat hypertension in obese patients. Which of the following detection methods would work best to identify the receptor in the different tissues affected by leptin? - correct answer western blot -The leptin receptor is a protein and located in the cell membrane of different tissue types. Detection of a protein can be done using a Western blot Ghrelin, the "hunger hormone," is released when the stomach is empty. It increases hunger and promotes secretion and motility in the digestive tract. The receptor for ghrelin is found on the same cells in the brain as the receptor for leptin. Which of the following is a true statement? - correct answer There is no interaction between leptin and ghrelin because they operate on separate receptors -they bind to the SAME cells in the brain, the fact that leptin and ghrelin bind to separate receptors means that there cannot be any kind of inhibition or interaction between them. They have seperate receptors, prevents any competitive inhibition. Brown fat will increase energy expenditure in the form of heat better than any other adipose tissue in the body. In brown fat, leptin indirectly activates uncoupling protein 1 (UCP-1) located in the inner mitochondrial membrane. UCP-1 activation will dissipate the proton gradient across the inner mitochondrial membrane and STOP which of the following reactions in mitochondria? - correct answer Oxidative phosphorylation -absence of the proton gradient across the inner mitochondrial membrane no electrochemical gradient has been built and the formation of ATP by ATP synthase, will not proceed. The ETC will continue and pass electrons along the transport chain, but the pumped protons will return to the matrix of the mitochondria with the help of UCP-1 activation The structure of (+)-fructose is shown below: How many chiral centers does (+)-fructose contain? - correct answer 3 chiral centers -Numbering from the TOP carbon down, C-3, C-4, and C-5 are chiral centers because they each have four different substituents Creatine phosphate is a high-energy buffer that helps maintain the level of available high-energy phosphates such as ATP. During intense muscular exertion, creatine phosphate replenishes the muscle's ATP by releasing a relatively larger amount of energy in transferring its phosphate group to ADP. ATP is able to accept this phosphate group from creatinine phosphate and serve as a convenient carrier of energy because: - correct answer it has phosphate groups with an intermediate transfer potential -ATP is good energy carrier bc it has an intermediate transfer potential. This allows higher energy phosphate carriers (creatine phosphate) to drive the synthesis of ATP by transferring their P-groups to ADP ATP - correct answer a particularly good energy carrier bc it has an intermediate transfer potential which allows higher energy phosphate carriers (like creatine phosphate) to drive the synthesis of ATP by transferring their phosphate groups to ADP has a varied role in the body, as an energy carrier and also as a nucleotide for RNA and DNA is present in every cell in the body Rank the following bonds in order of increasing polarity: C—Cl Cl—Cl Si—Cl P—Cl - correct answer Cl-Cl < C-Cl < P-Cl < Si-Cl -polarity of a bond depends on the difference in EN between the 2 bonding atoms: The larger the difference, the more unequal the sharing of electrons, the more polar. the Cl—Cl bond is completely nonpolar. Carbon is more EN than Si, therefore Cl, which is the most EN element depicted, will show the greatest EN difference with Si. Therefore the Si—Cl bond is most polar The sound level of a sound wave that is striking an eardrum is increased from 35 dB to 55 dB. By what factor has the intensity of the sound increased? - correct answer 100 -each increase by 10 in the decibel level, the intensity of the sound increases by a factor of 10. the decibel level has increased by 2 units of 10 (since 55 - 35 = 20 = 10 + 10), so the intensity increases by two factors of 10, 10^2 = 100. The ratio of products to reactants at equilibrium for Reaction 1 will change with a change in the: - correct answer temperature -only way to change a reaction's equilibrium constant is to change the temperature. in the forward direction, Reaction 1 may be considered: ATP + glutamate + NH3 => ADP + phosphate + glutamine - correct answer favorable, because the negative ΔG° for Reaction 2 more than compensates for the positive ΔG° for Reaction 3. -ΔG°2 + ΔG°3 < 0, so the overall reaction would be favorable and still be negative when added together G2= -3I G3= 14 Which of the following is true for Reaction 2, once it is allowed sufficient time to achieve equilibrium? ATP + H2O => ADP + phosphate ΔG° = -30.5 kJ/mol - correct answer ΔG > ΔG° -At equilibrium ΔG = 0. Since reaction 2 has a negative value of ΔG°, then ΔG > ΔG° In Reaction 1, the compound glutamine synthetase serves to: ATP + glutamate + NH3 => ADP + phosphate + glutamine - correct answer decrease the activation energy -catalyzed by the enzyme glutamine synthetase which catalyst increases the rate of a rxn by decreasing the Ea. Hypothetically, if Reaction I was found to be spontaneous at standard state and higher temperatures, but nonspontaneous at low temperatures, the reaction must result in: - correct answer increasing entropy and increasing enthalpy -From the equation ΔG = ΔH - TΔS, ΔH > 0 and ΔS < 0 would always give ΔG > 0 (nonspontaneous) no matter what the temperature. a ΔH < 0 and ΔS > 0 would give ΔG < 0 (spontaneous) regardless of temperature. -increasing both H & increasing S but at low temps would give +G Which one of the following expressions is equal to the pressure difference between Point c and Point d? - correct answer (ρliquid)gy -difference in pressure between two points in a static fluid is given by the expression where y is the vertical distance between the two points A healthy woman has a respiratory minute volume (the amount of air inhaled and exhaled in one minute) of about 6 L. Suppose the breathing tube she uses has a cross-sectional area of 1 cm2. What is the average flow speed through the tube? - correct answer 1 m/s -volume flow rate (volume of air flowing per second) is f = Av. The flow rate in this case is f = 6 L/min × (1 m3 / 1000 L) × (1 min / 60 s) = 1 × 10-4 m3/s. The cross-sectional area is 1 cm2 × (1 m / 100 cm)2 = 10-4 m2. Thus v = f / A = (1 × 10-4 m3/s) / (10-4 m2) = 1 m/s -solve for v in FAv eqn volume flow rate - correct answer volume of air flowing per second f= Av If the alcohol in the Pitot tube were replaced with water, then the height difference of the liquid in the U-tube for a given air speed would be: - correct answer smaller -equation given in the passage can be rearranged to show that y = v2ρgas / (2gρliquid) → y ∝ 1 / ρliquid. Since ρwater is greater than ρalcohol ρliquid increases causing y to decrease. -rearrange given equation for y-term which is indirectly proportional to density Which of the following graphs best illustrates how the height difference y of the liquid in the Pitot tube varies as the flow speed v of the air in the cylinder is changed? - correct answer Rearranging the equation given in the passage gives v = v2ρgas / (2gρliquid). y is proportional to v2, so the graph of yvs. v must be a parabola (through the origin) that opens upward In its interaction with the magnesium ion shown in Figure 1, Asn581 acts as which of the following? - correct answer lewis base -In the mechanism , Asn581 donates a lone pair to the magnesium metal ion acting as a ligand in the formation of a coordinate covalent bond lewis base - correct answer ligand electron pair donor -functions as an electron donor in an acid-base reaction by donates a lone pair -can donate to metal ion in the formation of a coordinate covalent bond lewis acid - correct answer electron pair acceptor bronsted base - correct answer proton (H+) acceptor bronsted acid - correct answer proton (H+) donor Based upon the data reported in Table 1, researchers chose one compound for further testing as a potential B-Raf inhibitor. Which compound was most likely to have been chosen? - correct answer PLX 3479 -smallest Kd value -substances were tested for their ability to bind the ATP binding pocket with high-affinity, the dissociation constant Kd, quantifies the dissociation of the ligand-protein complex. -Therefore, the substance that binds MOST strongly will have the smallest value for Kd. PLX 3479 possesses the greatest binding affinity as it has the smallest dissociation constant Kd - correct answer dissociation constant smaller the value, the stronger it binds possessing the greatest binding affinity = [ligand][protein] / [lig-protein complex] Researchers determined at 25°C, the rate constant for the binding of PLX 2021 to the B-Raf kinase domain ATP binding pocket is 2 x 10-2 M-1s-1. the rate constant for the dissociation of PLX 2021 from the B-Raf kinase domain ATP binding pocket is nearest what value? - correct answer 7 x 10-7 s-1 -Kd of PLX 2021-B-Raf kinase domain = to the ratio of the rate constants for the forward reaction (the dissociation of PLX 2021-B-Raf kinase domain) and the reverse reaction (the binding of PLX 2021 and the B-Raf kinase domain -the rate constant for the reverse reaction at the SAME temp is 2 x 10-2 M-1s-1, then the rate constant for t