*The Official January 2016 MCAT*

[Medaholic Dr]

Hello guys,
I don't see any thread made for January 2016 MCAT test date, so I thought to create one. I'll be graduating by the end of this year and will be giving my MCAT on January 2016. I had my test date set for September of this year, but something came up and I won't be able to dedicate myself to studying for the MCAT fully. So, let us make this thread rich with all the discussions about the MCAT. Let us support each other and make taking MCAT a pleasurable experience, so I think. Let's go.......

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[seriousmcattaker]

Are you sure that H has a +1 charge at physiological pH?? There was a question on the Section Bank where I believe it was not included

For MCAT purposes, saying that His has a positive charge (not +1, but some positive number) usually works just fine. If you want the real charge on His, you need to solve the Henderson Hasselbalch equation for a given pH. For example, standard extracellular pH is 7.4, and pKa of His is 6.0. So we can do this:

7.4 = 6.0 + log(His/HisH(+))

From that, you can find that (His/HisH(+)) ratio is about 25.12. Meaning, at pH 7.4, there are 25.12 times more deprotonated His than the protonated HisH(+) version. So from simple arithmetics, we can find the exact average charge as follows:

25.12 [HisH(+)] = [His]

and

[[[HisH(+)] x (+1)] + [[His] x (0)]]/[[HisH(+)]+[His]] = average charge on Histidine. This is just a weighted average based on molarities and the charges on the two forms of Histidine.

If we solve these two equations (just write [His] in terms of [HisH(+)] from the first equation, and plug it into the second one)

[[HisH(+)] x (+1)] / [26.12[HisH(+)] ] = 1/26 = +0.038.

So Histidine at the extracellular environment has an average charge of 0.038, hence we classify it as a positively charged amino acid. Intracellular pH is generally a little lower, ranging around 7. So, His would be more positively charged, around +0.091.

If all the calculations seem like an overkill, just think about this. When pH = pKa, half of the histidine side chains are protonated, half deprotonated. So, at pH = 6.0, the average charge on Histidine would be +0.5. When pH is 7.5, charge is +0.03, when pH is 4.5, charge is about +0.97, if you calculate the exact charge. But, for convention, if pH is more than 1.5 pH units above pKa, you can say that the deprotonated form will dominate and the charge is just 0 for histidine. If the pH is more than 1.5 pH units below pKa, the protonated form will dominate and the charge is simply +1 for histidine. If you go further than that, you would need to do separate calculations for the amino and carboxy ends of histidine, which will have their own pKa values. Also you should mind that Henderson Hasselbalch equation doesn't hold very well for pH values too far away from the pKa. I hope this was helpful.

 

[CHoge25]

Anyone have any idea why the AAMC uses the thin lens equation on number 11 on the chem section bank? The point 4cm away from the lens is shown as the point where the rays converge. Isn't this the actual definition of the focal point? So wouldn't the focal point just be 4cm? They treat this distance as the image distance.

I believe the

For MCAT purposes, saying that His has a positive charge (not +1, but some positive number) usually works just fine. If you want the real charge on His, you need to solve the Henderson Hasselbalch equation for a given pH. For example, standard extracellular pH is 7.4, and pKa of His is 6.0. So we can do this:

7.4 = 6.0 + log(His/HisH(+))

From that, you can find that (His/HisH(+)) ratio is about 25.12. Meaning, at pH 7.4, there are 25.12 times more deprotonated His than the protonated HisH(+) version. So from simple arithmetics, we can find the exact average charge as follows:

25.12 [HisH(+)] = [His]

and

[[[HisH(+)] x (+1)] + [[His] x (0)]]/[[HisH(+)]+[His]] = average charge on Histidine. This is just a weighted average based on molarities and the charges on the two forms of Histidine.

If we solve these two equations (just write [His] in terms of [HisH(+)] from the first equation, and plug it into the second one)

[[HisH(+)] x (+1)] / [26.12[HisH(+)] ] = 1/26 = +0.038.

So Histidine at the extracellular environment has an average charge of 0.038, hence we classify it as a positively charged amino acid. Intracellular pH is generally a little lower, ranging around 7. So, His would be more positively charged, around +0.091.

If all the calculations seem like an overkill, just think about this. When pH = pKa, half of the histidine side chains are protonated, half deprotonated. So, at pH = 6.0, the average charge on Histidine would be +0.5. When pH is 7.5, charge is +0.03, when pH is 4.5, charge is about +0.97, if you calculate the exact charge. But, for convention, if pH is more than 1.5 pH units above pKa, you can say that the deprotonated form will dominate and the charge is just 0 for histidine. If the pH is more than 1.5 pH units below pKa, the protonated form will dominate and the charge is simply +1 for histidine. If you go further than that, you would need to do separate calculations for the amino and carboxy ends of histidine, which will have their own pKa values. Also you should mind that Henderson Hasselbalch equation doesn't hold very well for pH values too far away from the pKa. I hope this was helpful.

Thank you for that very thorough explanation, I can tell you are a very serious mcat taker ..... So it seems to be settled that FOR THE SAKE OF THE MCAT that when at physiological pH histidine is "deprotonated"

 

[seriousmcattaker]

I believe the


Thank you for that very thorough explanation, I can tell you are a very serious mcat taker ..... So it seems to be settled that FOR THE SAKE OF THE MCAT that when at physiological pH histidine is "deprotonated"

That's right. Just make sure you remember that pKa isn't something "fixed" but can change according to the local environment. So in the active site of an enzyme, you may see "protonated" histidines, "protonated" glutamic acid, or "deprotonated" arginine etc. But the analysis works for a generic histidine at a generic location within the cell, or in a protein.

 

[sdonohu8]

Question regarding something from the scored exam:

On the question regarding the peptide amphiphile shown here, they ask which amino acid was incorporated into compound 1 as a future site of covalent attachment prior to HA. I know its the AA that is phosphorylated, but I'm confused as to how you would know this is a Serine and not an Alanine. It's common to see PO4- so I just assumed that the connecting oxygen came from phosphate. On the other hand, I see that you would probably need a Serine so that the increased reactivity would allow for phosphate bonding, but how would you know which one to pick definitively???

**edit: image wont upload, but I'm sure most of you know which passage I'm talking about

 

[laballsummer]

One more sort of general question regarding (usually viral) DNA incorporation. When the problem states something like... "a viral DNA sequence coding for a protein is inserted into a host genome. Given the resulting mRNA sequence, what was the original viral sequence?

Do we consider the viral DNA to be inserted as the coding or template strand? I would think template right?

 

[seriousmcattaker]

Question regarding something from the scored exam:

On the question regarding the peptide amphiphile shown here, they ask which amino acid was incorporated into compound 1 as a future site of covalent attachment prior to HA. I know its the AA that is phosphorylated, but I'm confused as to how you would know this is a Serine and not an Alanine. It's common to see PO4- so I just assumed that the connecting oxygen came from phosphate. On the other hand, I see that you would probably need a Serine so that the increased reactivity would allow for phosphate bonding, but how would you know which one to pick definitively???

**edit: image wont upload, but I'm sure most of you know which passage I'm talking about

You just gotta know that serine, threonine and tyrosine (the aa with -OH groups) are the ones that get phosphorylated in the cells. According to this https://en.wikipedia.org/wiki/Phosphorylation Histidine also can get phosphorylated in the eukaryotes in addition to the ones I mentioned. There is not a simple reaction that would phosphorylate the methyl end of an alanine (If you remember from beta oxidation, straight chain hydrocarbons have to be oxidized, hydrated etc. to make them reactive) but a simple substitution reaction works when you have an -OH group on it.

 

[Two_Hands]

Question regarding something from the scored exam:

On the question regarding the peptide amphiphile shown here, they ask which amino acid was incorporated into compound 1 as a future site of covalent attachment prior to HA. I know its the AA that is phosphorylated, but I'm confused as to how you would know this is a Serine and not an Alanine. It's common to see PO4- so I just assumed that the connecting oxygen came from phosphate. On the other hand, I see that you would probably need a Serine so that the increased reactivity would allow for phosphate bonding, but how would you know which one to pick definitively???

**edit: image wont upload, but I'm sure most of you know which passage I'm talking about

We are expected to know that Serine is the most commonly phosphorylated amino acid, followed by Threonine, Tyrosine, and some others. That came up on a few questions, I believe.

 

[colgatejake]

519 on Scored exam 131/128/131/129.

This is my target score and I am THRILLED, especially as a retake!

Interestingly, the Excel score predictor seems to predictor higher than the AAMC scored scale does. Most of my friends from the August exam found the Excel sheet to be a good predictor +- 1 point.

Not really sure what to do to bring up CARS, it feels so luck-based with the passages you get. Also, I'm missing more of the experimental design questions on P/S than I would expect to. ._.

I got the exact same scores bro, really hoping that i can bring that same level on friday, for CARS ive just been doing practice passages ive seen it go up a bit, but as CHoges said, its really a luck based thing i think. Im good at literature passages and economics and history and art, but im horrible at philosophy, so if they throw some Descartes in there i just make sure to do that last and get as many of the easier points as i can.

My target range is 515 to 521, and as long as i get +90th percentile ill be happy.

Best of luck!

 

[sdonohu8]

We are expected to know that Serine is the most commonly phosphorylated amino acid, followed by Threonine, Tyrosine, and some others. That came up on a few questions, I believe.

You just gotta know that serine, threonine and tyrosine (the aa with -OH groups) are the ones that get phosphorylated in the cells. According to this https://en.wikipedia.org/wiki/Phosphorylation Histidine also can get phosphorylated in the eukaryotes in addition to the ones I mentioned. There is not a simple reaction that would phosphorylate the methyl end of an alanine (If you remember from beta oxidation, straight chain hydrocarbons have to be oxidized, hydrated etc. to make them reactive) but a simple substitution reaction works when you have an -OH group on it.

Yeah, looked back in my notes from a few months ago and..there it was. Thank you!

 

[keshwa16]

So how many of you guys are taking the exam Saturday?

 

[CHoge25]

I got the exact same scores bro, really hoping that i can bring that same level on friday, for CARS ive just been doing practice passages ive seen it go up a bit, but as CHoges said, its really a luck based thing i think. Im good at literature passages and economics and history and art, but im horrible at philosophy, so if they throw some Descartes in there i just make sure to do that last and get as many of the easier points as i can.

My target range is 515 to 521, and as long as i get +90th percentile ill be happy.

Best of luck!

Descartes can go fall in a hole... I hate philosophy passages also, and I am not a fan of some of the art passages I see... 514+ all the way! We got this

 

[5sosfan]

Descartes can go fall in a hole... I hate philosophy passages also, and I am not a fan of some of the art passages I see... 514+ all the way! We got this

I'd be so ecstatic with a 514. Best of luck to everyone!

 

[flumadiddle]

I'm taking it on Saturday. For those on the east coast - do you think they'll be cancellations due to this snow storm that's approaching?

 

[Two_Hands]

I'm taking it on Saturday. For those on the east coast - do you think they'll be cancellations due to this snow storm that's approaching?

Potentially. Think they'd offer alternative date, or kick you to the road until spring?

 

[702599]

Just wanted to hop onto the forum to say good luck to everyone taking it this week!!! We are almost done with this thing!

 

[Rousey]

Can't wait for Friday night. I'm gonna wake up Saturday morning like this after I celebrate

 

[Snoopy528]

Could someone explain why a larger cross-sectional area increases nerve conduction velocity? Why is it different than fluids, where if you increase the cross-sectional area, the velocity of the fluid decreases?

Thanks!

 

[clathrin413]

Could someone explain why a larger cross-sectional area increases nerve conduction velocity? Why is it different than fluids, where if you increase the cross-sectional area, the velocity of the fluid decreases?

Thanks!

So I think of the nerve as I would a circuit, where you can model resistance as R = (resistivity)(length)/(area). Increasing area will then decrease R, and since I = V/R, you'll have a larger current. Since current is dQ/dt, this means faster conduction.

 

[5sosfan]

are you guys going over circular motion?

 

[Rousey]

Would gluconeogenesis occur during times of starvation when you need energy, or when you already have enough energy and you want to get rid of some pyruvate or OAA? TPR says it occurs when you already have enough energy, but that just doesn't make sense to me. It makes sense to make glucose during times of starvation when you need energy

 

[Snoopy528]

Thank you, clathrin413!

Rousey, I believe gluconeogenesis occurs during starvation, fasting, and exercise.

 

[seriousmcattaker]

Would gluconeogenesis occur during times of starvation when you need energy, or when you already have enough energy and you want to get rid of some pyruvate or OAA? TPR says it occurs when you already have enough energy, but that just doesn't make sense to me. It makes sense to make glucose during times of starvation when you need energy

Not necessarily during times of starvation. After you eat, the glucose in the food is the main source of blood glucose. That, however, is quickly stored as glycogen, then glycogenolysis is the main source of blood glucose. As glycogen stores go down, gluconeogenesis slowly increases to maintain the blood glucose. Gluconeogenesis reaches its peak when glycogen stores are gone, which happens about after a night of fasting. If fasting continues for more than a couple of days, the brain slowly switches over to ketone bodies for most of its energy needs, so gluconeogenesis slows down in order to preserve the body protein. I'm not sure what TPR means by "having enough energy", but this is the general picture of gluconeogenesis.

 

[clathrin413]

are you guys going over circular motion?

I haven't seen it on a single AAMC resource for the new test, it might be on the Physics QPack but I haven't done that. It's probably low yield, also as long as you know a = v^2/r you'll proly be ok.

I also haven't seen projectile motion or collisions on any of the new AAMC C/P stuff either, and they aren't explicitly in the outline. /shrugs.

 

[HopefulMed23]

Does anyone else feel like they're going to get a test that addresses their EXACT weaknesses, regardless of their scores on the practice test?

I know I do

 

[GEToutLADYits6AM]

I haven't seen it on a single AAMC resource for the new test, it might be on the Physics QPack but I haven't done that. It's probably low yield, also as long as you know a = v^2/r you'll proly be ok.

I also haven't seen projectile motion or collisions on any of the new AAMC C/P stuff either, and they aren't explicitly in the outline. /shrugs.

Those concepts are not on the this test anymore

 

[GEToutLADYits6AM]

I haven't seen it on a single AAMC resource for the new test, it might be on the Physics QPack but I haven't done that. It's probably low yield, also as long as you know a = v^2/r you'll proly be ok.

I also haven't seen projectile motion or collisions on any of the new AAMC C/P stuff either, and they aren't explicitly in the outline. /shrugs.

What is your method on verbal reasoning?

 

[keshwa16]

Potentially. Think they'd offer alternative date, or kick you to the road until spring?

I looked it up and found something on sdn from 2011. Apparently they don't do ****..you have to reschedule for the next available test date

 

[poloboy]

I looked it up and found something on sdn from 2011. Apparently they don't do ****..you have to reschedule for the next available test date

I'd rather fly myself to another state to get this MCAT over with than wait a few more months to take it in April!

 

[5sosfan]

I looked it up and found something on sdn from 2011. Apparently they don't do ****..you have to reschedule for the next available test date

that's bs.

 

[queenoftheclouds]

I'm doing the C/P Section Bank and it's ripping me a new one. The C/P section can't be this difficult on the mcat... right?! Even the FL and Sample C/P weren't like this. ;____;

 

[Sam93]

I'm doing the C/P Section Bank and it's ripping me a new one. The C/P section can't be this difficult on the mcat... right?! Even the FL and Sample C/P weren't like this. ;____;

IMO only a few passages will be this difficult on the mcat, but the majority will be easier.

 

[5sosfan]

IMO only a few passages will be this difficult on the mcat, but the majority will be easier.

Yea i'd say one or at the most two passages per section will be like the section bank.

 

[keshwa16]

I'd rather fly myself to another state to get this MCAT over with than wait a few more months to take it in April!

http://forums.studentdoctor.net/threads/mcat-cancellations-due-to-snow-storm.698880/

look at that thread from 2010

 

[Rousey]

I looked it up and found something on sdn from 2011. Apparently they don't do ****..you have to reschedule for the next available test date

Oh god. Now another thing I need to stress out about. I can't believe I'm saying this but snow... please stay away

 

[poloboy]

http://forums.studentdoctor.net/threads/mcat-cancellations-due-to-snow-storm.698880/

look at that thread from 2010

Well, that sucks. Let's hope ours won't get canceled.

 

[inthemaking1]

Not gonna lie, my heart's feeling a bit racy. I would really like some advice to calm the nerves and chill out or some encouragement.

 

[5sosfan]

Not gonna lie, my heart's feeling a bit racy. I would really like some advice to calm the nerves and chill out or some encouragement.

You'll do absolutely fine bro. Live life. Meditate. Listen to some music. Partake in the herb.

the mcat does not define your life. your friends, family, significant other, etc will always love you no matter what. this is not ****ing literal life or death.

 

[inthemaking1]

You'll do absolutely fine bro. Live life. Meditate. Listen to some music. Partake in the herb.

the mcat does not define your life. your friends, family, significant other, etc will always love you no matter what. this is not ****ing literal life or death.

Thanks bro, I really needed that!

 

[keshwa16]

Oh god. Now another thing I need to stress out about. I can't believe I'm saying this but snow... please stay away

sorry :/ My dad was talking about the weather this morning and I thought he was joking that there was going to be a snowstorm..

 

[poloboy]

Not gonna lie, my heart's feeling a bit racy. I would really like some advice to calm the nerves and chill out or some encouragement.

You'll do just fine dude. My PI told me the other day in the lab when he saw me studying for the MCAT, "You don't need to know all that. Just know carbon has four bonds." So yeah, I guess we've all overstudied.

 

[missmartian85]

Hey guys I'm taking my MCAT this Saturday, and I am simply a bundle of nerves! I just finished the MCAT Section bank and got scores of 85% C/P, 81% B/S, and UGH 75% P/S today. I can't seem to find much data out there about the section bank.... Does anyone know if these scores are ok?

 

[CHoge25]

Hey guys I'm taking my MCAT this Saturday, and I am simply a bundle of nerves! I just finished the MCAT Section bank and got scores of 85% C/P, 81% B/S, and UGH 75% P/S today. I can't seem to find much data out there about the section bank.... Does anyone know if these scores are ok?

Yeah you're good, section bank is harder than the other released ammc material. you should take one of the aamc tests to get a better feeling

 

[clathrin413]

Hey guys I'm taking my MCAT this Saturday, and I am simply a bundle of nerves! I just finished the MCAT Section bank and got scores of 85% C/P, 81% B/S, and UGH 75% P/S today. I can't seem to find much data out there about the section bank.... Does anyone know if these scores are ok?

I scored just a taaad higher than you on C/P and B/S and matched you on P/S in the Section Banks, got a 519 (131/128/131/129) on the Scored Exam a few days ago.

 

[missmartian85]

Yeah you're good, section bank is harder than the other released ammc material. you should take one of the aamc tests to get a better feeling

Thank-you for the words of encouragement it is much appreciated! I am planning on taking the AAMC scored FL tomorrow. I took the Sample Exam about a month ago and got a 511 so hoping the scored FL bodes as good or better results. I just want to get into my state school, so I am not hoping for crazy amazing results.

 

[missmartian85]

I scored just a taaad higher than you on C/P and B/S and matched you on P/S in the Section Banks, got a 519 (131/128/131/129) on the Scored Exam a few days ago.

Awesome! I am going to take the AAMC scored FL tomorrow and see how I do! Non-traditional student working while studying for this exam. It's been real........

 

[poloboy]

Awesome! I am going to take the AAMC scored FL tomorrow and see how I do! Non-traditional student working while studying for this exam. It's been real........

I totally get you! Studying for the MCAT is a full-time job in itself, so practically it's working two jobs.

 

[missmartian85]

I totally get you! Studying for the MCAT is a full-time job in itself, so practically it's working two jobs.

It's absolutely insane!! I thought working full time while doing undergrad was hard, but this is another story. Kudos to us I guess

Were you able to afford a prep class? I definitely couldn't with all my other obligations.

 

[poloboy]

It's absolutely insane!! I thought working full time while doing undergrad was hard, but this is another story. Kudos to us I guess

Were you able to afford a prep class? I definitely couldn't with all my other obligations.

Yeah, I thought digging through my notes from pre-med classes was time-consuming and more work, so I decided to do an online prep course, and it helped tremendously.

 

[missmartian85]

Yeah, I thought digging through my notes from pre-med classes was time-consuming and more work, so I decided to do an online prep course, and it helped tremendously.

Good for you! I wish I could have done an in-person one just for the comradery. Studying on my own has been an interesting experience

 

[missmartian85]

not that much over kill ....

Please - pyruvate
Can - Citrate
I - isocitrate
Keep - alpha ketogluterate
Swallowing - succinyl-CoA
Semen - succinate
For - fumarate
Money - malate
Officer - OAA

spelling may be off but thats the gist. just find yourself a good dirty mnemonic and you'll never forget it

Oh my goodness, thank-you for the laugh and the memory help!