AAMC Sample Test Chem/Phys Qs-Pt-2

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AAMC Sample Test Chem/Phys Qs-Pt-2

Post by svpatel » Fri Jan 24, 2020 12:59 pm

30. Where is the Data that helps me answer this question? I can’t find it. Ko is not given. I only have Ka/Ko. How did they get this ans? I picked A.increase the amount of CPFX bound to BSA.
but ans was B.decrease the amount of CPFX bound to BSA.

33. How can you tell that sites I and II recognize hydrophobic and anionic substrates? I don’t see that in the passage. Why anionic?

38. How does carbon labeling follow in this question? I picked C1,C3, and C5. Why is that wrong?

41. Neither reactant is chiral, but a chiral product forms because the catalyst (the enzyme) is chiral. Why does an enzyme give a chiral product? Isn’t an enzyme not supposed to mess with products and not change anything within it? Not sure about this one. I know enzymes def don't change themselves in a rnx, dec the activation energy by stabilizing the intermediate form. But thats it.

48. How do you get this ans? Why not C? This is so confusing. I get that ADP has two phosphates, but it could be AMP and the other phosphate could come from phosphopentothenate.

52. How does the eV and Columb relate to give joules? If I have eV and given e = 1.6 * 10^19C how do I get to J?

59. I don’t get how they are balancing it.
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Re: AAMC Sample Test Chem/Phys Qs-Pt-2

Post by NS_Tutor_Mathias » Sat Jan 25, 2020 2:00 am

30. The Ka/K0 ratios are however given. A ratio greater than 1 would mean Ka > K0, and a ratio less than 1 would mean Ka < K0. Therefore we know that for all metal ions, Ka < K0. So a lower affinity constant in the presence of any metal ion.

33. Ibuprofen is non-polar and warfarin has a carboxyl functional group. Ibuprofen can only interact with non-polar sites, and warfarin only really with cationic ones. The passage states that warfarin and ibuprofen bind to different sites respectively.

38. This is an aldol condensation mechanism that benefits from numbering carbons, particularly for reaction 2, to track where each radiolabeled carbon ends up. That is followed by a decarboxylation reaction to form IPP. I suggest you review first the link above first, and tomorrow I can post up a solution. In the meantime, try to draw these reactions out and track who the nucleophiles and electrophiles in each step must be.

41. Simply through it's structure. Nucleophilic attack on an sp2 carbon can result in either enantiomer being formed. But if local electron density (say because the reaction is happening on an enzyme, as is necessary for enzymatic catalysis) prohibits one product from forming, then the other will be the sole output. Alternatively, we can also simply see that none of the other options are true. A&B from the passage, and C from inferring that this is a biochemical reaction that occurs in an aqueous medium.

52. You can either just know that 1 eV = 1.6 * 10-19 J or remember that a V = J/C, and then convert.

Code: Select all

eV = e*J/C  ---> convert e to J as per conversion given, and you get just joules
It turns out that this gives the exact same figure as above, because the units of charge simply cancel out. That is why both eV and J are measures of energy.

59. You could write out both sides and literally count hydrogens and electrons on each side and write oxidation and reduction half reactions. If that is entirely unfamiliar after some review tomorrow, let me know. Alternatively, you can just draw out the structure given of pyruvate and realize that it must be gaining two hydrogens (or just read the structural formula) making everything besides A & D impossible. In answer choice A, we've added 4 electrons - something that is also evident as an impossibility from just drawing the bond-line notation of the reactants and products.

Additionally, this is a reaction that really needs to be excessively familiar for the MCAT. As far as the content outline goes, asking you to reproduce any step of glycolysis virtually from memory is not unheard of (although usually asked about in more subtle ways than this). On the bright side, questions like these, where material you should have memorized is given to you, are also very common.

For the two questions that I did not work through completely (38&59), definitely let me know if after working on them for part of a day you still haven't had any luck. But for the sake of your learning and improvement, you will be very well served spending some time reviewing and attempting to draw out the processes of these two questions.
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