The Official June 2015 MCAT Thread

[Abraxas305]

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So we can talk about all things MCAT 2015.
Just registered too!

 

[joshuak172]

hey guys, I'm looking for some advice. So I just took the AAMC sample test the other day and got 78% C/P, 81% CARS, 80% BIO, and 88% PSYCH/SOC under realistic test settings. I'm pretty satisfied with these scores given how April test takers have shown that ~80% and up is the marker for a good percentile, but this is the only full length that I have taken. I took the official guide questions about 2 months ago when I wasn't done with content review and did considerably worse in C/S and BIO, but given my sample test scores I'm not too worried about that. I've also done a ton of passages from TPR science workbook and the AAMC question packs. Originally I wasn't planning on doing practice tests from non-AAMC sources because I'm sure they're not reliable but it looks like a lot of other people seem to be doing it, so I'm worried I may be doing myself a disservice by not. At this late stage (I'm taking the exam in June), should I try out some of these other practice exams?

At this point, no. I would go over the AAMC test, 120 questions, and question packs with a fine-toothed comb identifying any remaining weaknesses. The other tests are just not at all indicative of the real thing (and may be more of a morale killer/waste of time) and you have already proven with your practice test score that you can handle the endurance of the test.

 

[SaintedHover]

Can anybody explain #38 from the physical sciences section? Thank you in advance!

 

[Caffein3]

Its definitely a Claissen condensation, and I believe acetyl-coa acting as a nucleophile and attacking the anhydride-esque structure. I started to draw out the mechanism..got frustrated and guessed haha

 

[Caffein3]

Heres a picture that @DrHart posted a while back in the April thread! Hope this helps.

 

[drrao88]

Okay I'll give it a shot.

#37:

I got this correct, but the reasoning and conflicting data in the passage are tripping me out.

The table in the passage reveals an increasing current, along with an increasing Resistance. However, I saw that the resistance seemed more correlated with temperature according to the passage, and so I kept R as the changing variable in V = IR, leading me to choice D, which correctly states that current (I) would have to decrease in order to compensate. My question here is:

How do you account for the discrepancy between the increasing current in the table vs. the correct answer, which assumes decreasing current?

#38:

I just plain out got this one wrong. I am not a visual person, so tracing carbons is not my thing. If anyone can explain this question clearly and concisely, please do!

#41:

Why can't the solvent medium be chiral?
And by that I mean, why cant it be composed of a solvent material that is chiral? Why does it HAVE to be the enzyme (I clearly understand A and B are wrong, I am just having trouble deducing between C and D)

#45:

What is the underlying concept of knowing that H2SO4 (or any strong acid) will hydrolyze an acetal? and cyanohydrin? Can someone explain why and how?

#52

If 140 kEV is the Energy (E) and 6.6 x 10^34 is Planck's constant (h), then (f) is then:

(140 x 10^3 eV )/ (6.6 x 10^-34) = 20.1 x 10^37
I am obviously making an error here, but where?!

 

[Caffein3]

Okay I'll give it a shot.

#37:

I got this correct, but the reasoning and conflicting data in the passage are tripping me out.

The table in the passage reveals an increasing current, along with an increasing Resistance. However, I saw that the resistance seemed more correlated with temperature according to the passage, and so I kept R as the changing variable in V = IR, leading me to choice D, which correctly states that current (I) would have to decrease in order to compensate. My question here is:

How do you account for the discrepancy between the increasing current in the table vs. the correct answer, which assumes decreasing current?

#38:

I just plain out got this one wrong. I am not a visual person, so tracing carbons is not my thing. If anyone can explain this question clearly and concisely, please do!

#41:

Why can't the solvent medium be chiral?
And by that I mean, why cant it be composed of a solvent material that is chiral? Why does it HAVE to be the enzyme (I clearly understand A and B are wrong, I am just having trouble deducing between C and D)

#45:

What is the underlying concept of knowing that H2SO4 (or any strong acid) will hydrolyze an acetal? and cyanohydrin? Can someone explain why and how?

#52

If 140 kEV is the Energy (E) and 6.6 x 10^34 is Planck's constant (h), then (f) is then:

(140 x 10^3 eV )/ (6.6 x 10^-34) = 20.1 x 10^37
I am obviously making an error here, but where?!

here's my best shot:
#37: how I thought at about it. temperature and resistance are correlated. as temperature goes up, so does resistance. therefore if we know the ratio that the temperature has increased (approximately ~2) then we know that the resistance has increased by 2 as well. Resistance is inversely prop. to current, so as the resistance is increasing as the temp increases, the current must be decreasing by that ratio, back down to the value given in the table. Hope that makes sense :/

#38 see above! Google claissen condensation mechanism to help understand!

#41: In chemistry a chiral ligand is a specially adapted ligand used for asymmetric synthesis. This ligand is an enantiopureorganic compound that combines with a metal center by chelation to form an asymmetric catalyst. This catalyst engages in a chemical reaction and transfers its chirality to the reaction product which as a result also becomes chiral. From Wikipedia. I learned in orgo that a chiral catalyst can induce chirality unto the product.

#45: the acid acts a catalyst that allows for the acetal to be electrophilic enough to be attacked by the water in the solution. Again, something I learned in orgo. Heres a good link to the picture of the mechanism. http://www.chem.wisc.edu/areas/reich/handouts/elecpush/ep-mechanisms.htm

#52: The charge of a photon is 1 eV which is 1.6x10^-19. Adjust your calculations and conversions and you'll get the correct answer 🙂

 

[drrao88]

Thanks!

For #41, Okay, I get that an enzyme can transfer chirality, but why can't a solvent?

BTW, if anyone wants to discuss this AAMC FL exam via phone, please PM me! I think that would be much more effective!

 

[Lavos]

Haven't taken an AAMC FL yet but these Kaplan tests are so demoralizing. I know people here said they did well on the AAMC questions/FL and didn't do as well on the Kaplan tests but it still sucks taking a 6 hour test and looking at how bad your score was lol

 

[Caffein3]

Yeah its rough to be honest. I'm honestly a bit frustrated with myself that I didn't finish content review earlier or access double AAMC practice passages until 1 month before. Studying during a full semester load was rough :/

 

[mikil100]

At this point I've stopped taking NS/TPR/Kaplan tests and am focusing on individual passages and the last EK exam/AAMC material. I don't want to get all bent out of shape before the exam due to a hypothetical "score"

 

[stressingout]

Can anyone explain to me #16 on the AAMC Sample Exam for the Chem/Phys section? I seem to have forgotten some organic.

 

[piii]

Can anyone explain to me #16 on the AAMC Sample Exam for the Chem/Phys section? I seem to have forgotten some organic.

Drew it out for you. This is part of the maltose which does have the hemiacetal, allowing it to be in equilibrium with the carbonyl open sugar form, giving the oxidizing agent access to the aldehyde to oxidize it to a carboxylic acid. This allows Ag to form a silver precipitate.

The sucrose doesn't have the hemiacetal, thus can't be in open chain form, so no access for the oxidizing agent. Look up the Benedicts test with Copper for reducing sugars. Allows you to distinguish between monosaccharides and glycogen polymers, where only hemiacetals, ketones, and aldehydes (monosaccharides) can be reduced and have a positive test, whereas acetal linkages in glycogen produce a negative test.


http://i.imgur.com/1cwxkZI.jpg

 

[stressingout]

Drew it out for you. This is part of the maltose which does have the hemiacetal, allowing it to be in equilibrium with the carbonyl open sugar form, giving the oxidizing agent access to the aldehyde to oxidize it to a carboxylic acid. This allows Ag to form a silver precipitate.

The sucrose doesn't have the hemiacetal, thus can't be in open chain form, so no access for the oxidizing agent. Look up the Benedicts test with Copper for reducing sugars. Allows you to distinguish between monosaccharides and glycogen polymers, where only hemiacetals, ketones, and aldehydes (monosaccharides) can be reduced and have a positive test, whereas acetal linkages in glycogen produce a negative test.


http://i.imgur.com/1cwxkZI.jpg

Okay, that make sense. Thank you!!! Would you also mind explaining 17 on that same exam? I thought a pH of 8 would make the environment mildly basic so that all the amino and carboxyl groups would be deprotonated, but that logic isn't correct. I just don't understand how to solve this problem without knowing pKa values.

 

[Caffein3]

Okay, that make sense. Thank you!!! Would you also mind explaining 17 on that same exam? I thought a pH of 8 would make the environment mildly basic so that all the amino and carboxyl groups would be deprotonated, but that logic isn't correct. I just don't understand how to solve this problem without knowing pKa values.

Well we know that in an Arg-Ala-Phe-Leu peptide, the only amino acid with a side chain that has any ionizable groups is arginine, so lets focus on that. At physiologic pH, the N-terminus and C-terminus exist in a "zwitterionic" state, where the amine group is protonated and the carboxyl is deprotonated, resulting in a neutral charge. So now, lets consider the side chain, which has a pKa of around ~12 and since we know that a molecule will be protonated until pH>pKa, that arginine residue exhibits a +1 charge. Does that make sense?

 

[mikil100]

I feel like I'm running out of sources for good practice. Going through the TPR science workbook and it just does not have the MCAT feel at all.

 

[stressingout]

Well we know that in an Arg-Ala-Phe-Leu peptide, the only amino acid with a side chain that has any ionizable groups is arginine, so lets focus on that. At physiologic pH, the N-terminus and C-terminus exist in a "zwitterionic" state, where the amine group is protonated and the carboxyl is deprotonated, resulting in a neutral charge. So now, lets consider the side chain, which has a pKa of around ~12 and since we know that a molecule will be protonated until pH>pKa, that arginine residue exhibits a +1 charge. Does that make sense?

You mean pH<Pka? I know how to calculate it if I have the pKa value, but it wasn't given to us. Do we have to memorize pKa values!? I certainly hope not...

Also, physiological pH is ~7.4 so does it not matter that it's slightly above that? I guess what I'm asking it what is the acceptable range for us to consider it "physiological pH"?

 

[drrao88]

You mean pH<Pka? I know how to calculate it if I have the pKa value, but it wasn't given to us. Do we have to memorize pKa values!? I certainly hope not...

Also, physiological pH is ~7.4 so does it not matter that it's slightly above that? I guess what I'm asking it what is the acceptable range for us to consider it "physiological pH"?

You dont have to memorize pKa values.

What you do you have to know is the pKa of an amino group and a carboxyl group, which are 9. something and 2. something, respectively.

If the arginine is basic (more than one amino group) then at a pH BELOW its pKA, it will be in an environment with enough hydrogen ions for the amino groups to accept these hydrogen ions and possess a +1 charge.

 

[stressingout]

You dont have to memorize pKa values.

What you do you have to know is the pKa of an amino group and a carboxyl group, which are 9. something and 2. something, respectively.

If the arginine is basic (more than one amino group) then at a pH BELOW its pKA, it will be in an environment with enough hydrogen ions for the amino groups to accept these hydrogen ions and possess a +1 charge.

Ahh so we can roughly figure out pKa values from the structure. Got it! Thank you!!!

 

[piii]

Ahh so we can roughly figure out pKa values from the structure. Got it! Thank you!!!

The logic behind this comes from Le Chatelier's Principal.

For a weak acid (pKa > 0): HA <-> H+ + A-
pH < pKa, protonated and neutral. Overabundance of H+ shifts equilibrium to the left.
pH > pKa, deprotonated and negative. Less H+ shifts equilibrium to the right.

For a base: B + H+ <-> BH+
pH < pKa, protonated and positive. High H+ shifts reaction to right.
pH > pKa, deprotonated and neutral. Low H+ shifts reaction to left.

Now, as other have said, the backbone of every amino acid has a basic NH2 (pKa ~ 9) and acidic COOH (pKa ~ 4).
So in physiologic pH, or really anything that between the pKa's of the amino acid backbone, then by the above stated rules you have a + and - charge, that cancel out.

This applies from every polar neutral and non polar hydrophobic amino acid.
For the polar acidic and basic groups, the additional R group adds addition charge according to the rules above.

I actually would recommend memorizing a few pKa's. Not too bad.

Polar Acidic:
Aspartic Acid (Asp D) and Glutamic Acid (Glu E) ~ pKa 4

Polar Basic:
Histidine (His H) ~ pKa 6.5 - this is actually close to physiological pH and so can either be an acid or base and is prevalent at protein active sites.
Arginine (Arg R) ~ pKa 12
Lysine (Lys K) ~ pKa 10

 

[Caffein3]

Just memorizing those 5 or so pKa's will be more than helpful. Not that bad! Just slap them on your notecards.

 

[piii]

Ahh so we can roughly figure out pKa values from the structure. Got it! Thank you!!!

Also just thought of a few other pKa's to memorize (not related to Amino Acids though).

CH4 ~ 48
alpha hydrogen of carbonyl ~ 20
Alcohol and water ~ 16
Phenol ~ 10
Carboxylic acid ~ 4

Can be seriously useful for saving time with acid base questions, as well as extractions, charges, etc.

 

[Caffein3]

Did not like the physics pack from AAMC. Raw physics is my weakness. I do fine on the conceptual stuff, but equations bleehhhh

 

[drrao88]

Question on #45 on the BS section of the AAMC:

Why would a muscle cell depleted in oxygen be producing a significant amount of Glucose 6-Phosphate?

My understanding is that during anaerobic respiration, the cell continuously produces lactic acid, and so without Oxygen, the pyruvate will NOT be converted into acetyl coA.

Hence, I get the logic behind the correct answer choice, but why in the HELL would the cell be PRODUCING G6P?!

I can understand if it was TRANSPORTING in glucose and then converting to G6P, but the production of G6P is an energy consuming process, is it not?. I would think that in times of low oxygen availability the cell would be catabolizing G6P for whatever energy is available. Or do they mean production in terms of glycogen breakdown? (which is not necessarily production, but perhaps I am thinking into this too much)

Can someone elaborate on how to make the deduction between G6P and acetyl CoA, moreso focusing on why G6P WOULD be produced?!

Thanks!

 

[piii]

Question on #45 on the BS section of the AAMC:

Why would a muscle cell depleted in oxygen be producing a significant amount of Glucose 6-Phosphate?

My understanding is that during anaerobic respiration, the cell continuously produces lactic acid, and so without Oxygen, the pyruvate will NOT be converted into acetyl coA.

Hence, I get the logic behind the correct answer choice, but why in the HELL would the cell be PRODUCING G6P?!

I can understand if it was TRANSPORTING in glucose and then converting to G6P, but the production of G6P is an energy consuming process, is it not?. I would think that in times of low oxygen availability the cell would be catabolizing G6P for whatever energy is available. Or do they mean production in terms of glycogen breakdown? (which is not necessarily production, but perhaps I am thinking into this too much)

Can someone elaborate on how to make the deduction between G6P and acetyl CoA, moreso focusing on why G6P WOULD be produced?!

Thanks!

Glycogen phosphorylase is stimulated in low energy states and thus conversion of Glycogen to Glucose 1 Phosphate, and then to G6P is increased.

 

[drrao88]

Glycogen phosphorylase is stimulated in low energy states and thus conversion of Glycogen to Glucose 1 Phosphate, and then to G6P is increased.

Okay thanks! I was understanding the idea of G6P production to imply energy-consuming Gluconeogenesis, which doesn't happen in muscle anyways.

Question for BS section #58:

(I just want to confirm that my logic is correct)

In asking which substitution will decrease the entropic penalty, they mean to ask "Which amino acid substitution will increase the disorder and disrupt the overall protein folding?" correct?

For choice (D), why isn't the conversion of Arginine (polar basic) to Tryptophan (non-polar, neutral) going to increase the disorder, and thereby largely decrease the "entropic penalty?"

 

[piii]

Okay thanks! I was understanding the idea of G6P production to imply energy-consuming Gluconeogenesis, which doesn't happen in muscle anyways.

Question for BS section #58:

(I just want to confirm that my logic is correct)

In asking which substitution will decrease the entropic penalty, they mean to ask "Which amino acid substitution will increase the disorder and disrupt the overall protein folding?" correct?

For choice (D), why isn't the conversion of Arginine (polar basic) to Tryptophan (non-polar, neutral) going to increase the disorder, and thereby largely decrease the "entropic penalty?"

It is asking, which AA substitution would reduce the energy and make the protein folding more favorable. By saying penalty, they are implying that there is a energy cost in the protein's original configuration. A hydrophobic AA (Leu) on the surface interacting with water would be highly unfavorable. Substituting Thr, a polar, neutral molecule just like water, with an OH group for H bonding would result in the most favorable substitution.

 

[Caffein3]

Okay thanks! I was understanding the idea of G6P production to imply energy-consuming Gluconeogenesis, which doesn't happen in muscle anyways.

Question for BS section #58:

(I just want to confirm that my logic is correct)

In asking which substitution will decrease the entropic penalty, they mean to ask "Which amino acid substitution will increase the disorder and disrupt the overall protein folding?" correct?

For choice (D), why isn't the conversion of Arginine (polar basic) to Tryptophan (non-polar, neutral) going to increase the disorder, and thereby largely decrease the "entropic penalty?"

yeah the wording on this threw me off. I selected the most unfavorable substitution, instead of the most favorable.

 

[stressingout]

The wording is definitely weird but I interpreted "penalty" as bad. It said which would decrease the entropic penalty, so which would decrease this bad thing, meaning which is the best or most favorable. Not sure if that was the right way to go about it but it got me the correct answer. Just my two cents in case another weirdly worded question comes up!

 

[GEToutLADYits6AM]

Anyone know how to do number 59 of the physical science?

 

[Sir.SavaLottaLife]

I finally feel like I'm getting better at verbal! I started off with 7's on the old aamc 11 and first few EK 101 tests but now I've started making 10's in EK and I'm getting ~75-80% correct in my other timed CARS/verbal sessions. I haven't taken a FL in a few weeks but I'm taking two more before the big day. (EK and AAMC sample)

 

[stressingout]

Anyone know how to do number 59 of the physical science?

Yes, if you look at all the answer choices, it's all the same general reaction except the coefficients vary. For answer choices B and C, the equations are not balanced because there are too many hydrogen ions on the left side. If you write out the oxidation reduction reaction with the electrons (I think it's given in the AAMC explanation), you will see that in order to cancel out those 2 electrons, the coefficient in front of NADH has to be 1. From there, we arrive to the answer of D.

 

[stressingout]

I finally feel like I'm getting better at verbal! I started off with 7's on the old aamc 11 and first few EK 101 tests but now I've started making 10's in EK and I'm getting ~75-80% correct in my other timed CARS/verbal sessions. I haven't taken a FL in a few weeks but I'm taking two more before the big day. (EK and AAMC sample)

I know how you feel! I used to get 7's on old MCAT practice materials as well and now I'm averaging upper 70% to lower 80% on CARS! But I can't help but worry that the conversion scale will be much more unforgiving since the new MCAT allows us more time... I'm worried that even if I score well in terms of percent correct, the actual percentile will not be as good...what do you think the 50th percentile for CARS will be?

 

[drrao88]

I know how you feel! I used to get 7's on old MCAT practice materials as well and now I'm averaging upper 70% to lower 80% on CARS! But I can't help but worry that the conversion scale will be much more unforgiving since the new MCAT allows us more time... I'm worried that even if I score well in terms of percent correct, the actual percentile will not be as good...what do you think the 50th percentile for CARS will be?

Nice!

Also, take the AAMC soon! You want to give yourself a lot of time to go over it. More than any other practice FL.

 

[Caffein3]

I am so hit or miss on CARS! Its either I get all the questions right or I just struggle hard and miss 3 or 4 in a passage. Like on the AAMC I got like 25 correct in a row, and then one passage comes up and I missed 4 on it! Crossing my fingers that we all just get nice CARS passages 😀

 

[SaintedHover]

I am so hit or miss on CARS! Its either I get all the questions right or I just struggle hard and miss 3 or 4 in a passage. Like on the AAMC I got like 25 correct in a row, and then one passage comes up and I missed 4 on it! Crossing my fingers that we all just get nice CARS passages 😀

THIS IS ME!!!! Lol

I just hope we get interesting passages that won't put me to 😴

 

[Sir.SavaLottaLife]

I know how you feel! I used to get 7's on old MCAT practice materials as well and now I'm averaging upper 70% to lower 80% on CARS! But I can't help but worry that the conversion scale will be much more unforgiving since the new MCAT allows us more time... I'm worried that even if I score well in terms of percent correct, the actual percentile will not be as good...what do you think the 50th percentile for CARS will be?

But you have to remember that you will also be a beneficiary of this added time. That can be a good thing if time is a big factor for you, or it may disadvantage you slightly if you always finished in early.

Personally, I'm a slow reader and time has always been a factor for me. Todays session was the first time I had time to read every passage (old format, ~8.5 min per passage). One of TPR FL's I took before I guessed completely on 3 of the 9 passages and ended up with a 124.

And I attribute this factor to the bulk of my improvement lately. After doing dozens and dozens of passages in the past couple months untimed (but with a sense of urgency to finish within a reasonable amount of time) I became familiar with the questions types and right vs. wrong answer choices. I feel like my reading speed and comprehension have only improved marginally at best. After starting timed sessions again, I still struggled a bit but I started cracking 8's. And lately I've made strides in my strategy / timing to push me up to 9/10's (75%-80%). I still have my work cut out for me, but its just exciting to finally see some sort of improvement because my science scores have always been excellent but verbal/CARS has haunted me for a while now and at times made me feel like my chances of going MD were shot.

 

[piii]

I am so hit or miss on CARS! Its either I get all the questions right or I just struggle hard and miss 3 or 4 in a passage. Like on the AAMC I got like 25 correct in a row, and then one passage comes up and I missed 4 on it! Crossing my fingers that we all just get nice CARS passages 😀

Same. On TPR CARS questions I usually get 1-2 wrong. I find their passages very challenging. But in the AAMC CARS packs, the sample test and the official guide, I get 80-85% right. Here's hoping thats not just a fluke! I took the MCAT 3 years ago and got great scores and a remedial 6th grade Chinese ESL student score on verbal.. Really messed me up. I think I'm in the right play intellectually now, so fingers crossed!

 

[Sir.SavaLottaLife]

Same. On TPR CARS questions I usually get 1-2 wrong. I find their passages very challenging. But in the AAMC CARS packs, the sample test and the official guide, I get 80-85% right. Here's hoping thats not just a fluke! I took the MCAT 3 years ago and got great scores and a remedial 6th grade Chinese ESL student score on verbal.. Really messed me up. I think I'm in the right play intellectually now, so fingers crossed!

The CARS sections on TPR's FL's can be ridiculous, don't beat yourself up about it.

 

[Profound]

@Sir.SavaLottaLife Nice work! I'm rooting for you all the way. Always nice to see someone start to see improvement, especially in the CARS/Verbal section. You give me hope as I'm still trying to figure out CARS. Just keep pushing!

To everyone else, you're almost there! Good luck guys!

 

[mikil100]

My CARS scores started around what would be an ~8 on the old exam and have plateaued at what would be an ~11 after getting used to timing and the question types. I think AAMC material is much easier than the prep companies, too. We're gonna rock this thing! I'm taking my last EK exam today. I'll post scores when done

 

[stressingout]

But you have to remember that you will also be a beneficiary of this added time. That can be a good thing if time is a big factor for you, or it may disadvantage you slightly if you always finished in early.

Personally, I'm a slow reader and time has always been a factor for me. Todays session was the first time I had time to read every passage (old format, ~8.5 min per passage). One of TPR FL's I took before I guessed completely on 3 of the 9 passages and ended up with a 124.

And I attribute this factor to the bulk of my improvement lately. After doing dozens and dozens of passages in the past couple months untimed (but with a sense of urgency to finish within a reasonable amount of time) I became familiar with the questions types and right vs. wrong answer choices. I feel like my reading speed and comprehension have only improved marginally at best. After starting timed sessions again, I still struggled a bit but I started cracking 8's. And lately I've made strides in my strategy / timing to push me up to 9/10's (75%-80%). I still have my work cut out for me, but its just exciting to finally see some sort of improvement because my science scores have always been excellent but verbal/CARS has haunted me for a while now and at times made me feel like my chances of going MD were shot.

I didn't get into MD last cycle because of my verbal score!! Ahh it's great to hear how much you've improved. Best of luck 🙂

 

[scratchrice]

Can anyone explain Ka and Km's to me? On the AAMC FL I treated Ka as I would Km in the PS section (questions 30-33) where a smaller value would indicate greater affinity for the substrate but this was the wrong mentality and I got two of those questions wrong. If Km can determine substrate affinity, why is it that a greater Ka value indicates greater affinity when the opposite is true for Km? I'm just kinda frustrated because in the bio section they also used Kt but it represented Km as well, and not Ka. Hopefully Im making some sense....

 

[Caffein3]

In the passages, Ka and Kd simply refer to association and dissociation constants, respectively. While they are often used in regards to enzymes, proteins, and ligands, they can be for any complex that breaks apart or comes together, e.g. sodium bicarbonate has a dissociation constant and association constant, because it can come together or break apart. From my understanding, Km specifically refers to inhibition of an enzyme, and it is the substrate concentration at which the reaction rate is at half of Vmax.

So, in terms of strength of binding and more:
decreased Km: tighter binding of enzyme to substrate
decreased Kd: tighter binding of enzyme to ligand (or just in general for any molecule; harder to break apart into respective pieces)
increased Ka: tighter binding of enzyme to ligand (or just in general for any molecule; it comes together and complexes easier)

This is my understanding of it. May be wrong though 😛

 

[Mr. Beefy Lion]

Just took AAMC sample test:

Chem/phys: 88%
CARS: 83%
Bio/biochem: 81%
Psych/soc: 86%

I'm shocked that I scored above a 70% on cars....I never scored above 70% on Cars. I'm afraid this was a fluke cars score :/

 

[SaintedHover]

Has anybody done the 120 question packs from AAMC?

Working on the Bio version 1 and not really liking it at all.

 

[GCSDOC]

Just took AAMC sample test:

Chem/phys: 88%
CARS: 83%
Bio/biochem: 81%
Psych/soc: 86%

I'm shocked that I scored above a 70% on cars....I never scored above 70% on Cars. I'm afraid this was a fluke cars score :/

nice scores! did you find the guide questions harder than the sample test?

 

[stressingout]

Just took AAMC sample test:

Chem/phys: 88%
CARS: 83%
Bio/biochem: 81%
Psych/soc: 86%

I'm shocked that I scored above a 70% on cars....I never scored above 70% on Cars. I'm afraid this was a fluke cars score :/

Nice!! What's your strategy on the chem/phys section?

 

[stressingout]

Has anybody done the 120 question packs from AAMC?

Working on the Bio version 1 and not really liking it at all.

I just finished the bio version 1! I thought it required more outside info while the mcat 2015 bio section is more about interpreting/analyzing data presented in the passage. I personally think the question packs are easier just because I'm better at regurgitating information than analyzing

 

[SaintedHover]

I just finished the bio version 1! I thought it required more outside info while the mcat 2015 bio section is more about interpreting/analyzing data presented in the passage. I personally think the question packs are easier just because I'm better at regurgitating information than analyzing

I am about half way through and I would agree that it does require more outside knowledge. I guess it is good to see what we know/don't know but I don't think we will have many questions like the ones in the pack.

 

[mikil100]

I just finished the bio version 1! I thought it required more outside info while the mcat 2015 bio section is more about interpreting/analyzing data presented in the passage. I personally think the question packs are easier just because I'm better at regurgitating information than analyzing

The bio packs were significantly easier, IMO. I scored 93% on each of them. Kind of wish I took the old MCAT.



I just finished EK's third exam. I really hate taking prep company tests because they just demoralize so much.
PS: 58%
CARS: 68% (worst yet)
Bio: 80%
Psych: 73%

Overall 70%

Not really sure how I feel about PS. On one hand I feel like their PS section is ridiculously hard compared to AAMC material, on the other hand a 58% is still very bad. For CARS I'm really not concerned because EK has poorly written Verbal tests, and I traditionally score 85%+ on CARS from actual AAMC material. Bio and Psych are meh.