TBR Carbohydrates

[dray5150]

Does anybody think the TBR Passages on Carbohydrates is a little overboard?? I'm doing significantly worse on these then others and I'm debating if I should spend the time on understanding the specifics being 3 weeks away from the exam. Hats off to all the other sections though.

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[txprodigal]

Yeah, it was a little bit much, but if you know that section, you'll have probably covered all your bases for that particular topic come test time.

 

[229141]

I personally think that they won't have that much carbohydrates on the mcat...the reactions specifically.

But yeah if you know that stuff theres no way they could get you

 

[BerkReviewTeach]

Does anybody think the TBR Passages on Carbohydrates is a little overboard?? I'm doing significantly worse on these then others and I'm debating if I should spend the time on understanding the specifics being 3 weeks away from the exam. Hats off to all the other sections though.

A good general rule to follow is that if it has significance in biology, then it has some likelihood of showing up. If it's purely chemistry (like the Wohl rxn, Benedict's test, etc...), then it's there just to CYA and can probably be skipped. Kiliani Fisher synthesis is about the only pure chemistry topic from that section to have down for the MCAT.

 

[229141]

A good general rule to follow is that if it has significance in biology, then it has some likelihood of showing up. If it's purely chemistry (like the Wohl rxn, Benedict's test, etc...), then it's there just to CYA and can probably be skipped. Kiliani Fisher synthesis is about the only pure chemistry topic from that section to have down for the MCAT.

Ok this is good to know!

I liked this chapter for the most part though...was a great refresher from my biochem class actually.

What chapter I REALLY liked was the amino acids one...actually went into detail about proline turns and significance of cysteine etc. Loved it

 

[Segovia]

Ok this is good to know!

I liked this chapter for the most part though...was a great refresher from my biochem class actually.

What chapter I REALLY liked was the amino acids one...actually went into detail about proline turns and significance of cysteine etc. Loved it

Totally, I also liked the shortcut to finding the PI of a protein! For the carbohydrates, it is nice to be quick in interconverting between straight-chain and Haworth, but who knows if this will be just a cool party trick or useful for the MCAT. Either way, we will gain nerd respect.

 

[229141]

Totally, I also liked the shortcut to finding the PI of a protein! For the carbohydrates, it is nice to be quick in interconverting between straight-chain and Haworth, but who knows if this will be just a cool party trick or useful for the MCAT. Either way, we will gain nerd respect.

TBR did a great job of making Ochem fun...I didn't like the first 2 chapters but from then on I oddly enjoyed studying it

 

[capostat]

The first part of the Carbohydrate chapter with rotating the fisher projections is bugging me. Do we really have to know how to identify the stereochemisty of the sugar?

I dont recall doing it for fisher projections. Having to rotate it and stuff...EK definitely didnt go into it, so is it safe to skip?

 

[0Complications]

The first part of the Carbohydrate chapter with rotating the fisher projections is bugging me. Do we really have to know how to identify the stereochemisty of the sugar?

I dont recall doing it for fisher projections. Having to rotate it and stuff...EK definitely didnt go into it, so is it safe to skip?

You need to know how to rotate bonds for Ochem, not necessarily Bio, but it will appear in the same section.

I think bond rotating is more than I've seen on any practice exams to date. Normally the organic questions are pretty superficial, like is this R or S, how many stereocenters are on this molecule kind of stuff.

 

[capostat]

You need to know how to rotate bonds for Ochem, not necessarily Bio, but it will appear in the same section.

I think bond rotating is more than I've seen on any practice exams to date. Normally the organic questions are pretty superficial, like is this R or S, how many stereocenters are on this molecule kind of stuff.

In general I'm ok with that. Maybe I'm just a little forgetful, but I dont believe that EK covered the issue of stereochemistry using Fisher projections. Because they never discussed the orientation of the bonds relative to one another in Fisher projections.

TBR also went into discussion about how the stereochemisty at the "penultimate" carbon denotes D or L. That's why I wanted to know how much detail into carbohydrate organic chemistry is required.

By the way, what's the difference between a "stereogenic center", and a "chiral" one. If we can only talk stereochemisty business when we are talking about 4 unique substituents, why even bother to give a label to something that, I assume--doesnt have 4 unique substituents...

 

[0Complications]

In general I'm ok with that. Maybe I'm just a little forgetful, but I dont believe that EK covered the issue of stereochemistry using Fisher projections. Because they never discussed the orientation of the bonds relative to one another in Fisher projections.

TBR also went into discussion about how the stereochemisty at the "penultimate" carbon denotes D or L. That's why I wanted to know how much detail into carbohydrate organic chemistry is required.

By the way, what's the difference between a "stereogenic center", and a "chiral" one. If we can only talk stereochemisty business when we are talking about 4 unique substituents, why even bother to give a label to something that, I assume--doesnt have 4 unique substituents...

D and L are just simply whether the bottom substituent is on the left side (L) or the right side (D). That's it.

For the stereocenter/chiral question, they are the same thing. you need 4 different substituent groups on a carbon (you can have them on other atoms as well, but that's beyond the scope of the exam).

Also reamember stereoisomers. Those are simply 2^n (n= # of stereocenters).

That IS tested.

 

[capostat]

ok cool thanks...

i just looked at the AAMC topics list and i saw that the CYCLIC structures should be known. Now BR has a method of converting the Haworth projections into the straight chain, but is that really necessary to learn? I just studied some tricks for learning the fisher projections for common sugars. i hope a stucture question is asked using that structure, cause if we have to know the cyclic one....

 

[capn jazz]

so should we know the structure of glucose?

 

[capostat]

so should we know the structure of glucose?

in Fisher--I would think, but I didnt bother studying the up/down orientations of the -OH's in the rings. maybe I'm taking chances.

if not the exact structure between aldoses, then maybe just distinguish between aldoses and ketoses, and pentoses and hexoses?

ribose =pentose, aldose
glucose=hexose, aldose
fructose=hexose,ketose

 

[0Complications]

in Fisher--I would think, but I didnt bother studying the up/down orientations of the -OH's in the rings. maybe I'm taking chances.

if not the exact structure between aldoses, then maybe just distinguish between aldoses and ketoses, and pentoses and hexoses?

ribose =pentose, aldose
glucose=hexose, aldose
fructose=hexose,ketose

I don't think you need to know it, but if you do just think, Right, Left, Right, Right. That's the orientation of the OH groups. Then if you are going to convert it, anomeric carbon one is carbon 5 and the groups that are on the right are now on the bottom, then the orientation of the OH group on anomeric carbon one is going to be either beta or alpha. Beta = Both C 6 and the OH are up, alpha is if C6 is up and the OH is down. 😉

But, like I said, I doubt you will need to know that. It will probably be passage based if you get one. Or what is carbon "X" called. Or something to that effect.

 

[0Complications]

ok cool thanks...

i just looked at the AAMC topics list and i saw that the CYCLIC structures should be known. Now BR has a method of converting the Haworth projections into the straight chain, but is that really necessary to learn? I just studied some tricks for learning the fisher projections for common sugars. i hope a stucture question is asked using that structure, cause if we have to know the cyclic one....

Just understand resonance and huckles rule and you should be fine.

 

[EgyptianDoc]

so should we know the structure of glucose?

You probably don't need to know it but I'll tell you the way I think about it since it requires no thought really. When you think of glucose think of "flipping the bird" or giving the finger with your right hand. Your thumb is the aldehyde portion (HC=O) and your fingers are the OH groups. C2, 4, and 5 curl inward so you know that those OH groups are on the right leaving C3 on the left. C6 is just the CH2OH group. Now you just know it. If you forget, give yourself the finger 😀. Oh and why right hand? Because that gives the OH on C5 the D-configuration, which is the type of configuration found in living organisms. If you didn't already know that, remember the mnemonic "Sugar D-addy." For the sake of being complete, amino acids in living organisms have the L-configuration.

 

[dragon529]

That mnemonic is actually from TBR O-chem... which I found to be helpful as well =D

 

[capostat]

I don't think you need to know it, but if you do just think, Right, Left, Right, Right. That's the orientation of the OH groups. Then if you are going to convert it, anomeric carbon one is carbon 5 and the groups that are on the right are now on the bottom, then the orientation of the OH group on anomeric carbon one is going to be either beta or alpha. Beta = Both C 6 and the OH are up, alpha is if C6 is up and the OH is down. 😉

But, like I said, I doubt you will need to know that. It will probably be passage based if you get one. Or what is carbon "X" called. Or something to that effect.

I'll definitely know alpha/beta anomers. But the conversion between say chair, and fisher conformation can be something that becomes clouded when trying to remember. i guess i'm paying it too much detail though.

 

[capn jazz]

You probably don't need to know it but I'll tell you the way I think about it since it requires no thought really. When you think of glucose think of "flipping the bird" or giving the finger with your right hand. Your thumb is the aldehyde portion (HC=O) and your fingers are the OH groups. C2, 4, and 5 curl inward so you know that those OH groups are on the right leaving C3 on the left. C6 is just the CH2OH group. Now you just know it. If you forget, give yourself the finger 😀. Oh and why right hand? Because that gives the OH on C5 the D-configuration, which is the type of configuration found in living organisms. If you didn't already know that, remember the mnemonic "Sugar D-addy." For the sake of being complete, amino acids in living organisms have the L-configuration.

hahaha that's great but I'm having a little trouble visualizing it. What fingers on my hand are C2, 3, 4, 5? And why do I have 6 fingers?

 

[EgyptianDoc]

hahaha that's great but I'm having a little trouble visualizing it. What fingers on my hand are C2, 3, 4, 5? And why do I have 6 fingers?

Just imagine flicking off someone sideways with your right hand and that your hand is rotated 90 so that your middle finger is pointing straight to the left. You are looking at the orientation of your fingers as you do this. Is that more clear?

Thumb = C1 (HC=O)
Index = C2 (curls inward to the right)
Middle = C3 (points left)
Ring = C4 (curls inward to the right)
Pinky = C5 (curls inward to the right)
C6? Unless you have polydactyly just remember that it's CH2OH 🙂

lol, got it?

 

[capn jazz]

Just imagine flicking off someone sideways with your right hand and that your hand is rotated 90 so that your index finger is pointing straight to the left. You are looking at the orientation of your fingers as you do this. Is that more clear?

Thumb = C1 (HC=O)
Index = C2 (curls inward to the right)
Middle = C3 (points left)
Ring = C4 (curls inward to the right)
Pinky = C5 (curls inward to the right)
C6? Unless you have polydactyly just remember that it's CH2OH 🙂

lol, got it?

Awesome, thanks. now I just have to come up with a reason to tell the proctor when she asks why I'm flipping off the computer. 😀

 

[EgyptianDoc]

Just imagine flicking off someone sideways with your right hand and that your hand is rotated 90 so that your index finger is pointing straight to the left. You are looking at the orientation of your fingers as you do this. Is that more clear?

Thumb = C1 (HC=O)
Index = C2 (curls inward to the right)
Middle = C3 (points left)
Ring = C4 (curls inward to the right)
Pinky = C5 (curls inward to the right)
C6? Unless you have polydactyly just remember that it's CH2OH 🙂

lol, got it?

Awesome, thanks. now I just have to come up with a reason to tell the proctor when she asks why I'm flipping off the computer. 😀

Haha . I made a mistake... I bolded it above. That should say middle finger obviously, lol. As long as you get it, sweet! You know there's a camera on top of the computer right? Make sure the person watching doesn't think you're flipping them off lol.

 

[EgyptianDoc]

The mind is a funny thing. Because I bet now you will just remember that it's R, L, R, R. You don't even need this dumb memory aid to remember it. Now on to more important things 🙂. Time is of the essence my friend.