The Official 4/26/13 MCAT Thread

[clothcut]

In lieu of the other threads popping up, I thought it'd be good for those of us taking the test to identify ourselves 👍

I'm not planning on following a rigid study schedule until January, but I think I'm going to watch a single video off of wikipremed daily to lightly review.

Good luck to everyone... we will crush this exam..

---

Members don't see this ad.

 

[Status Sciaticus]

I'm out. Good night guys.
Good job on the guidebook score gandalf

Based on the scale of AAMC 11, you scored the upper end of 12. Good job!

thanks. I figured it would be 11's scale.

im debating on whether I should do the PS tonight or leave it for tomorrow and do the remaining questions on TBR physics (sound waves/fluids tonight)

 

[HotHamH2O]

thanks. I figured it would be 11's scale.

im debating on whether I should do the PS tonight or leave it for tomorrow and do the remaining questions on TBR physics (sound waves/fluids tonight)

stay up with me! im about to start PS from guidebook now.

 

[Status Sciaticus]

stay up with me! im about to start PS from guidebook now.

alrighty! just lemme get a quick cup of coffee and 2-3 games of call of duty in before i start the PS.

 

[osprey099]

alrighty! just lemme get a quick cup of coffee and 2-3 games of call of duty in before i start the PS.

lol..

 

[Status Sciaticus]

lol..

whatever works right?

😎

 

[Postictal Raiden]

Could someone be so kind and give me a brief on immunology? This is my weakest area in bio.

I know that there are two types of immunology:
1. Innate (nonspecific, skin, acidity of stomach, blood flow, macrophages, etc...)
2. Acquired (humoral and cell-mediated)

I also know that humoral immunity refers to B-cells that make antibodies, and that cell-mediated immunology refers to T-cells that either killer cells that present foreign proteins on their surface or activate B-cells.

However, I don't know the details regarding CD4, CD8, MHCI and MHCII, and how T and B-cells work together to kill pathogens.

Thanks

 

[Status Sciaticus]

Could someone be so kind and give me a brief on immunology? This is my weakest area in bio.

I know that there are two types of immunology:
1. Innate (nonspecific, skin, acidity of stomach, blood flow, macrophages, etc...)
2. Acquired (humoral and cell-mediated)

I also know that humoral immunity refers to B-cells that make antibodies, and that cell-mediated immunology refers to T-cells that either killer cells that present foreign proteins on their surface or activate B-cells.

However, I don't know the details regarding CD4, CD8, MHCI and MHCII, and how T and B-cells work together to kill pathogens.

Thanks

all you have to know is generalizations

innate - non specific stuff that kills foreign pathogens aka macrophages and non specific cytokines.

cell mediated- T cell immunity (cd4 helpers cd8 killer)

Humoral - plasma cell/b cell antibody response.

MHC II shows up on plasma cells and MHC I is usually on cells that are infected or contain pathogen particles (neutrophils, macrophages).

 

[HotHamH2O]

finished the gen chem part of the guidebook...woof. it was tricky. I am not happy. lol

onto physics

 

[Status Sciaticus]

finished the gen chem part of the guidebook...woof. it was tricky. I am not happy. lol

onto physics

ill let you know mine once i finish physics lol.

 

[HotHamH2O]

just want to say...I cannot imagine any calculations this involved on the real mcat as the one's I am seeing in the guidebook physics right now. if so...finishing will be impossible for me. that is all

ps - apparently we are supposed to know that P = 4pi*r^2[I2} = 32pi W

lol gtfo

 

[Status Sciaticus]

just want to say...I cannot imagine any calculations this involved on the real mcat as the one's I am seeing in the guidebook physics right now. if so...finishing will be impossible for me. that is all

ps - apparently we are supposed to know that P = 4pi*r^2[I2} = 32pi W

lol gtfo

Yea I'm not doing physics tonight. 7 am is when I'll start.

 

[HotHamH2O]

Yea I'm not doing physics tonight. 7 am is when I'll start.

wuss

 

[thing]

Hey everyone, I'm taking the exam on the 27th but I have a quick question:


I understand that hydrostatic pressure is equal to (density)*(gravity)*(depth) but I don't understand how you calculate depth. I think there was a question like this in AAMC 9...do you count the depth from the bottom of the fluid to top or top of the fluid to air?

For example, if a glass of water was only 1/4 full, would the depth be the 1/4 of fluid or the 3/4 of air that's above it? I'm kind of confused on that. Also any other important stuff about hydrostatic pressure we should know?

 

[milski]

Hey everyone, I'm taking the exam on the 27th but I have a quick question:


I understand that hydrostatic pressure is equal to (density)*(gravity)*(depth) but I don't understand how you calculate depth. I think there was a question like this in AAMC 9...do you count the depth from the bottom of the fluid to top or top of the fluid to air?

For example, if a glass of water was only 1/4 full, would the depth be the 1/4 of fluid or the 3/4 of air that's above it? I'm kind of confused on that. Also any other important stuff about hydrostatic pressure we should know?

For hydrostatic pressure of the fluid, it will be top of the fluid to the bottom of the fluid, so 1/4 in your example.

 

[Back 5]

just want to say...I cannot imagine any calculations this involved on the real mcat as the one's I am seeing in the guidebook physics right now. if so...finishing will be impossible for me. that is all

ps - apparently we are supposed to know that P = 4pi*r^2[I2} = 32pi W

lol gtfo

What question was that? I don't remember using Pi for any calculations in the guidebook physics.

EDIT: Ahh, yes. The sound intensity question. That question was really hard. I knew the sound intensity was 10e-4 due to the Db change, but I have no idea how they got 4. I had chosen A.

 

[osprey099]

Well I JUST woke up.. got about 5 hours of sleep. Got about 6 hours of sleep the previous night. Idk if I should just go to bed for another 2 hours or just stay up cause I gotta wake up around 7am tomorrow but recently I've been having trouble staying awake.

 

[Back 5]

Well I JUST woke up.. got about 5 hours of sleep. Got about 6 hours of sleep the previous night. Idk if I should just go to bed for another 2 hours or just stay up cause I gotta wake up around 7am tomorrow but recently I've been having trouble staying awake.

No caffeine after 2-3pm today, try to refrain from taking naps in the afternoon. Try to get to bed around 10pm if you are planning on waking up anytime between 5-6am for an 8am test. Should allow you to be well rested tomorrow.

 

[osprey099]

No caffeine after 2-3pm today, try to refrain from taking naps in the afternoon. Try to get to bed around 10pm if you are planning on waking up anytime between 5-6am for an 8am test. Should allow you to be well rested tomorrow.

Thanks for the advice. I'm definitely not going to take any naps today. I've refrained from doing so the past couple of days. However, it's going to be almost impossible for me to go to sleep at 10pm b/c that's so early compared to when I've been going to bed for the past 3 years (around 2am) lol. I don't really need to get up that early since the test center is just 10 minutes away. I think I'm going to go to sleep at midnight and wake up around 7am.

 

[MedGrl@2022]

Last day of studying guys... lets make it count... going to finish reviewing AAMC 11 and go over the new guidebook, practice verbal and review some of the areas i am less comfortable in

What are your plans?

 

[Albein]

Will they let us into the testing center today?

 

[Back 5]

How many formula are you all planning on memorizing for a memory dump tomorrow? Looking over my formula sheet that I created, I think I have some formula on there that have a low likelihood of showing up.

I am worried about my mind blanking and forgetting an easy formula though, especially when I am anticipating every second counting.

So, are you planning on memorizing 30-40 formula between physics and gen chem?

 

[Albein]

How many formula are you all planning on memorizing for a memory dump tomorrow? Looking over my formula sheet that I created, I think I have some formula on there that have a low likelihood of showing up.

I am worried about my mind blanking and forgetting an easy formula though, especially when I am anticipating every second counting.

So, are you planning on memorizing 30-40 formula between physics and gen chem?

I wouldn't bet on them allowing a formula dump during the tutorial. They didnt let me last year.

 

[Back 5]

Will they let us into the testing center today?

Why wouldn't they? Worst case scenario is you go and they are closed.

 

[Back 5]

I wouldn't bet on them allowing a formula dump during the tutorial. They didnt let me last year.

That 10 minute tutorial is my time to do whatever I want. If some proctor walks up to me and says I cannot write formulas during my test, you better believe I will raise cain.

 

[MedGrl@2022]

I am baffled by this organic chemistry question. It is a discrete for AAMC 11.

Item 107. The disaccharides (+)-maltose and (+)-cellobiose are composed of two D-glucose subunits. The structural differences are a result of:

A) alpha- versus beta- glucoside linkages
B) chair versus boat conformations in the glucose subunits
C) constitutional isomerism
D) 5- versus 6-membered rings in the glucose subunits

I chose C but the answer is A.

So what did I miss in my MCAT studying that I need to know in order to solve this problem... am I supposed to know what makes up (+) maltose and (+) cellobiose?

How were you able to solve this problem?

Thank you!

 

[Albein]

That 10 minute tutorial is my time to do whatever I want. If some proctor walks up to me and says I cannot write formulas during my test, you better believe I will raise cain.

You're right but the proctor last year didnt let me and she made it a point to say I wasn't allowed to write in the booklet until I started the exam

 

[MedGrl@2022]

You're right but the proctor last year didnt let me and she made it a point to say I wasn't allowed to write in the booklet until I started the exam

There is no exam booklet right? Can't you just write on the scrap paper that they provide?

 

[Back 5]

I am baffled by this organic chemistry question. It is a discrete for AAMC 11.

Item 107. The disaccharides (+)-maltose and (+)-cellobiose are composed of two D-glucose subunits. The structural differences are a result of:

A) alpha- versus beta- glucoside linkages
B) chair versus boat conformations in the glucose subunits
C) constitutional isomerism
D) 5- versus 6-membered rings in the glucose subunits

I chose C but the answer is A.

So what did I miss in my MCAT studying that I need to know in order to solve this problem... am I supposed to know what makes up (+) maltose and (+) cellobiose?

How were you able to solve this problem?

Thank you!

I believe the +/- designation here is referring to optical rotation, which means the difference has to be based on bonds. Chair/Boat conformation will not affect optical rotation.

Constitutional isomers simply mean you have the same molecular formula but arranged in different ways. Think of a primary vs secondary vs tertiary pentanol. Same formula, different arrangement of the molecule.

 

[Back 5]

You're right but the proctor last year didnt let me and she made it a point to say I wasn't allowed to write in the booklet until I started the exam

Then you should have thrown a fit. As soon as you are given your scratch paper or booklet, sit at the computer and enter the tutorial, you have started your exam.

 

[Albein]

Then you should have thrown a fit. As soon as you are given your scratch paper or booklet, sit at the computer and enter the tutorial, you have started your exam.

Fair enough. I guess I didn't want the added stress, especially because I didn't sleep. If that happens this time around, I'm throwing a fit for sure. Maybe I'll even throw in that AAMC said it was ok

 

[Moxess]

I am baffled by this organic chemistry question. It is a discrete for AAMC 11.

Item 107. The disaccharides (+)-maltose and (+)-cellobiose are composed of two D-glucose subunits. The structural differences are a result of:

A) alpha- versus beta- glucoside linkages
B) chair versus boat conformations in the glucose subunits
C) constitutional isomerism
D) 5- versus 6-membered rings in the glucose subunits

I chose C but the answer is A.

So what did I miss in my MCAT studying that I need to know in order to solve this problem... am I supposed to know what makes up (+) maltose and (+) cellobiose?

How were you able to solve this problem?

Thank you!

The key is that they tell you they're both made of 2 D-glucose monosaccharides. That means the only difference between them is the way those 2 glucoses are linked. You did actually kinda have to know what alpha and beta linkages are, though, because if you thought the linkages were from different carbons, C would be a plausible answer.

Alpha and Beta refer to the orientation of the OH group on the anomeric carbon (the one next to the O in the ring on a monosaccharide). Alpha means it's trans to the CH2OH group, known to it's close friends as carbon 6 of glucose in this case; beta means it's cis to that CH2OH. The thing to note here is that disaccharides will almost always form linkages between the same 2 carbons, so the difference is in the orientation of that linkage. When you talk about polysaccharides like cellulose and glycogen and amylase, you get into branching and 1-4 vs 1-2 linkages, which might be worth reviewing as well.

 

[MedGrl@2022]

I am baffled by this organic chemistry question. It is a discrete for AAMC 11.

Item 107. The disaccharides (+)-maltose and (+)-cellobiose are composed of two D-glucose subunits. The structural differences are a result of:

A) alpha- versus beta- glucoside linkages
B) chair versus boat conformations in the glucose subunits
C) constitutional isomerism
D) 5- versus 6-membered rings in the glucose subunits

I chose C but the answer is A.

So what did I miss in my MCAT studying that I need to know in order to solve this problem... am I supposed to know what makes up (+) maltose and (+) cellobiose?

How were you able to solve this problem?

Thank you!

Wait I think I figured it out. So basically they are saying that these two disacchrides are the same but different... they wouldn't be constitutional isomers of eachother and the ring structures wouldnt change since glucose is a 6 membered ring... glucose is capable of being either an alpha or beta anomer right... depending on if it points up or down... since they are composed of the same monosaccharides it would be reasonable to conclude that they only vary in their glucoside linkages, right?

What does the (+) mean? How they rotate light?

 

[osprey099]

I am baffled by this organic chemistry question. It is a discrete for AAMC 11.

Item 107. The disaccharides (+)-maltose and (+)-cellobiose are composed of two D-glucose subunits. The structural differences are a result of:

A) alpha- versus beta- glucoside linkages
B) chair versus boat conformations in the glucose subunits
C) constitutional isomerism
D) 5- versus 6-membered rings in the glucose subunits

I chose C but the answer is A.

So what did I miss in my MCAT studying that I need to know in order to solve this problem... am I supposed to know what makes up (+) maltose and (+) cellobiose?

How were you able to solve this problem?

Thank you!

For this question, you needed to infer that cellobiose refers to something cellulose related. You should know that humans cannot digest cellulose because cellulose has beta 1-4 linkage. Humans can digest maltose because maltose has alpha 1-4 linkages.

 

[MedGrl@2022]

The key is that they tell you they're both made of 2 D-glucose monosaccharides. That means the only difference between them is the way those 2 glucoses are linked. You did actually kinda have to know what alpha and beta linkages are, though, because if you thought the linkages were from different carbons, C would be a plausible answer.

Alpha and Beta refer to the orientation of the OH group on the anomeric carbon (the one next to the O in the ring on a monosaccharide). Alpha means it's trans to the CH2OH group, known to it's close friends as carbon 6 of glucose in this case; beta means it's cis to that CH2OH. The thing to note here is that disaccharides will almost always form linkages between the same 2 carbons, so the difference is in the orientation of that linkage. When you talk about polysaccharides like cellulose and glycogen and amylase, you get into branching and 1-4 vs 1-2 linkages, which might be worth reviewing as well.

So although it was not an option the answer could have also been 1,4; 1,6; 1,1 linkages right? Should I memorize the structures of sucrose, maltose, lactose, cellulose, amylose, amylopectin, and glycogen? I am thinking of reviewing the TBR chapter on carbohydrates... do you think that should cover it?

 

[MedGrl@2022]

So although it was not an option the answer could have also been 1,4; 1,6; 1,1 linkages right? Should I memorize the structures of sucrose, maltose, lactose, cellulose, amylose, amylopectin, and glycogen? I am thinking of reviewing the TBR chapter on carbohydrates... do you think that should cover it?

Should I know how to discern between names of carbohydrates and 1,4; 1,6; 1,1 linkages?

 

[osprey099]

Do you guys think we will need to know the mechanism of organic chemistry reactions like nucleophilic acyl substitution of carboxylic acids + derivatives, diels alder, hoffman elimination, etc or do you guys think this information will be provided in the passage?

 

[MedGrl@2022]

Do you guys think we will need to know the mechanism of organic chemistry reactions like nucleophilic acyl substitution of carboxylic acids + derivatives, diels alder, hoffman elimination, etc or do you guys think this information will be provided in the passage?

I think most of this info will be in the passage... but sometimes it might not be... thus, try to have an idea of the mechanism

 

[Status Sciaticus]

Good morning peeps. I kinda overslept by 1.5 hours today 😴

oh well. Time to get cracking!

 

[MedGrl@2022]

Passage 1 in BS was confusing me... I think I understand it better now that I am reviewing it... for some reason I thought that all the controls were also receiving pericytes... why do you think that in A-C that the controls had different growth rates? All the controls in A-C were just ECs, right?

 

[GemelloMD]

So although it was not an option the answer could have also been 1,4; 1,6; 1,1 linkages right? Should I memorize the structures of sucrose, maltose, lactose, cellulose, amylose, amylopectin, and glycogen? I am thinking of reviewing the TBR chapter on carbohydrates... do you think that should cover it?

Disaach.
Sucrose- glucose Alpha-1,2 Fructose
Lactose- galactose Beta 1,4 Glucose

Polysaccharides.
Maltose- glucose Alpha 1,4 Glucose (fairly branched)
Cellulose - glucose Beta 1,4 Glucose (pretty straight chained)

This should be sufficient.

Interesting Note: sucrose is actually an alpha glucose- beta fructose dimer. However, it looks like an alpha glucose Backwards alpha Fructose. This is because the fructose is actually inverted in order to have the anomeric carbon (C-2, not C-1, because it is a ketose) bond to the anomeric carbon of glucose. ( this is different from something like maltose who has an anomeric carbon bonding to a C-4 carbon). So, if given the structure of sucrose and asked the orientation of the anomeric carbon of fructose, even though it looks alpha, it's beta. Overkill, perhaps. But my mind remembers the broad sweeps in light of the minutia.

 

[MedGrl@2022]

Good morning peeps. I kinda overslept by 1.5 hours today 😴

oh well. Time to get cracking!

don't fret... you will have a more productive studying day! 🙂

 

[HotHamH2O]

Fair enough. I guess I didn't want the added stress, especially because I didn't sleep. If that happens this time around, I'm throwing a fit for sure. Maybe I'll even throw in that AAMC said it was ok

So you did confirm with AAMC that you can do this during the tutorial?

 

[HotHamH2O]

It's a good mornin' for bacon.

 

[WSHRocks]

Could someone be so kind and give me a brief on immunology? This is my weakest area in bio.

I know that there are two types of immunology:
1. Innate (nonspecific, skin, acidity of stomach, blood flow, macrophages, etc...)
2. Acquired (humoral and cell-mediated)

I also know that humoral immunity refers to B-cells that make antibodies, and that cell-mediated immunology refers to T-cells that either killer cells that present foreign proteins on their surface or activate B-cells.

However, I don't know the details regarding CD4, CD8, MHCI and MHCII, and how T and B-cells work together to kill pathogens.

Thanks

I can expand a little bit on what Gandalf said:

The simplified model for cell-mediated immunity is that you have two major types of T cells: helper and cytotoxic T-cells. Scientists use the protein markers CD4 (helper) and CD8 (cytotoxic) to identify them, as these proteins are a key part of their interaction with MHCs. MHCI interacts with CD8 co-receptor, the T-cell receptor of cytotoxic T-cells, and the antigenic protein, while MHCII interacts with CD4, TCR of helper T-cells, and the antigenic protein. I remember this as MHCI, where "I" marks the primary function of the immune system (kill off the bug), and MHCII "II" as the secondary function of enhancing the attack through help.

In viral infections, for example, cytotoxic T-cells release granules containing perforin and granzyme B, which induce apoptosis of the virus-infected cell. Helper T-cells can activate B cells to send out antibodies against viral proteins that they recognize in their CD4-TCR-antigen complex. B cells then become plasma cells, which produce vast amounts of antibody specific for the antigen. These antibodies are then recognized by the complement system, and that is all gobbled up then by macrophages.

I will also just add that it's good to know that there is at least one further major type of T cell, the regulatory T cell (Treg), which acts to inhibit/tone down the response of lymphocytes (T, B cells) to antigen. Tregs are thought to prevent auto-immune responses and to prevent organ rejection for very well-matched MHC donor/recipients (suppression by Tregs is definitely not strong enough for a partial/full allogeneic mismatch).

I think this is sufficient for the MCAT, but let me know if you have any more questions about it.

 

[MedGrl@2022]

Passage 1 in BS was confusing me... I think I understand it better now that I am reviewing it... for some reason I thought that all the controls were also receiving pericytes... why do you think that in A-C that the controls had different growth rates? All the controls in A-C were just ECs, right?

Also passage 3 of BS section. The + under "Killing CTLs" in table 1 means that the mouse model has that function right?!

So by inactivating myosin Va, the only result is that they are albino? But, if you inactivate Rab27a the mouse does not have killing functionality of CTLs and is albino?

This is weird to me because in paragraph two, they were saying how Rab27a aids in the transfer of the melanosome to myosin Va.

Am I misunderstanding something?

 

[Albein]

So you did confirm with AAMC that you can do this during the tutorial?

Nope but I figure if I said that, they wouldn't argue haha

 

[MedGrl@2022]

Also passage 3 of BS section. The + under "Killing CTLs" in table 1 means that the mouse model has that function right?!

So by inactivating myosin Va, the only result is that they are albino? But, if you inactivate Rab27a the mouse does not have killing functionality of CTLs and is albino?

This is weird to me because in paragraph two, they were saying how Rab27a aids in the transfer of the melanosome to myosin Va.

Am I misunderstanding something?

okay Item 122 BS of AAMC 11... I got it right but couldn't two isoenzymes be caused by alternative splicing/editing of the mRNA. I was trying to find that in the answer choices or anything that was near that. I was skeptical picking C "DNA that code for cP-450".

Anyone have any thoughts on this?

 

[MedGrl@2022]

okay Item 122 BS of AAMC 11... I got it right but couldn't two isoenzymes be caused by alternative splicing/editing of the mRNA. I was trying to find that in the answer choices or anything that was near that. I was skeptical picking C "DNA that code for cP-450".

Anyone have any thoughts on this?

Anyone available to help me with some questions that I have on AAMC 11?

 

[WSHRocks]

Also passage 3 of BS section. The + under "Killing CTLs" in table 1 means that the mouse model has that function right?!

So by inactivating myosin Va, the only result is that they are albino? But, if you inactivate Rab27a the mouse does not have killing functionality of CTLs and is albino?

This is weird to me because in paragraph two, they were saying how Rab27a aids in the transfer of the melanosome to myosin Va.

Am I misunderstanding something?

Yeah, + means has that function. If you inactivate myosin Va, you can't move the melanosome along the cytoskeleton to release it, causing albinism. If you inactivate Rab27a, the melanosome can't bind myosin Va, so the mice are albino, but not necessarily with or without CTL activity. Based on the evidence in the table, they do not have CTL activity either, which must mean that Rab27a is present in lytic granules as well as melanosomes and is necessary for release of lytic granules from CTLs.

 

[WSHRocks]

okay Item 122 BS of AAMC 11... I got it right but couldn't two isoenzymes be caused by alternative splicing/editing of the mRNA. I was trying to find that in the answer choices or anything that was near that. I was skeptical picking C "DNA that code for cP-450".

Anyone have any thoughts on this?

I suppose it could be, but that was not an answer choice, so you have to deal with the answers given. Isozymes/isoenzymes are typically only different by a few amino acids, not an entire spliced region. I don't know of any examples, but I can't rule it out either. Usually, each isozyme has its own specific tissue, and many tissues have only certain regions of DNA open for transcription (as a result of differentiation), so it would make sense that each isozyme specific to a tissue would have its own promotor region and thus a DNA region separate from the other isozymes. I think that questions like these are better off deducing from the answers given rather than inducing from the evidence provided, especially when the topic is unfamiliar.