Amino Acids?

[mcgst9]

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On the practice exams from TPR, I recall seeing a few questions about them that seemed very specific.

Other than they way they bond together (the peptide bonds), is there anything else we should know about them for the actual MCAT?

 

[brood910]

On the practice exams from TPR, I recall seeing a few questions about them that seemed very specific.

Other than they way they bond together (the peptide bonds), is there anything else we should know about them for the actual MCAT?

You have to know specific properties for some of them.

e.g. which ones are optically inactive.

 

[Marnoona]

You have to know specific properties for some of them.

e.g. which ones are optically inactive.

And also through my recent readings, you need to recognize which ones are acidic, basic, neutral etc...

 

[mcgst9]

And also through my recent readings, you need to recognize which ones are acidic, basic, neutral etc...

Acids end it "-ate" or "acid" right? Glutamate/Asparate?

Is there anything specific for the basic ones that makes them easy to remember? Or just remember their names? Histidine/Arginine/Lysine?

You have to know specific properties for some of them.

e.g. which ones are optically inactive.

Which ones besides glycine are optically inactive?

 

[Marnoona]

Acids end it "-ate" or "acid" right? Glutamate/Asparate?

Is there anything specific for the basic ones that makes them easy to remember? Or just remember their names? Histidine/Arginine/Lysine?



Which ones besides glycine are optically inactive?

I actually remember the basic amino acids based on their side chains. However, you can determine their basicity through their ability of being protonated and form a positive charge (amines are basic). Also, for acids, they form negative charge when they deprotonate (COOH -> COO-). You also need to note that there are neutral but polar amino acids, such as asparagine and glutamine (the amide group isn't basic). They are called neutral because they aren't acidic nor basic, but are polar because they can form hydrogen bonds.

Glycine is the only amino acid that isn't chiral, so it isn't optically active. 18 amino acids demonstrate S-configuration, except cysteine (it has R-configuration). Overall, 19 amino acids are chiral and are optically active, and 1 amino acid (glycine) is nonchiral and optically inactive.

 

[mcgst9]

I actually remember the basic amino acids based on their side chains. However, you can determine their basicity through their ability of being protonated and form a positive charge (amines are basic). Also, for acids, they form negative charge when they deprotonate (COOH -> COO-). You also need to note that there are neutral but polar amino acids, such as asparagine and glutamine (the amide group isn't basic). They are called neutral because they aren't acidic nor basic, but are polar because they can form hydrogen bonds.

Glycine is the only amino acid that isn't chiral, so it isn't optically active. 18 amino acids demonstrate S-configuration, except cysteine (it has R-configuration). Overall, 19 amino acids are chiral and are optically active, and 1 amino acid (glycine) is nonchiral and optically inactive.

😱

I feel like the vast majority of this information is biochemistry based D=

I don't think I am going to spend too much time on this stuff though, at most, it will cost me one question.

 

[Marnoona]

😱

I feel like the vast majority of this information is biochemistry based D=

I don't think I am going to spend too much time on this stuff though, at most, it will cost me one question.

It actually is . Just remember the acidic, basic ones, glycine is the only one that isn't chiral, and you will be fine i guess 🙂.

 

[mcgst9]

It actually is . Just remember the acidic, basic ones, glycine is the only one that isn't chiral, and you will be fine i guess 🙂.

I figure, if they show me an amino acid structure, I can probably figure out how it will behave. I could never just name it off the top of my head though unless it was one of the acids and only one was listed or it was Glycine just because it's not chiral.

I am sure most questions involving them probably come with a passage as well.

 

[Marnoona]

I figure, if they show me an amino acid structure, I can probably figure out how it will behave. I could never just name it off the top of my head though unless it was one of the acids and only one was listed or it was Glycine just because it's not chiral.

I am sure most questions involving them probably come with a passage as well.

Yes, when i was practicing several passages of organic chem from TPR, they usually focused on acid/basic stuff, along with the configurations (R/S etc...). Best of luck! 🙂.

 

[gettheleadout]

Just memorize their structures. It's low effort over ≥1 month and it can only help. Obviously know the categorizations too (acidic, basic, non-polar, semi-polar, hydrophilic).

 

[milski]

Just memorize their structures. It's low effort over ≥1 month and it can only help. Obviously know the categorizations too (acidic, basic, non-polar, semi-polar, hydrophilic).

It's a waste of time and one of the things that I wish I had ignored. It seems that TBR cares a lot about it but AAMC would not bother to test it.

It's moderately low effort for extremely low (virtually 0) yield.

Of course, I cannot prove or support what I'm saying in any practical manner, so..

 

[Synapsis]

The likelihood of getting the question of "which amino acid is this structure" seems so incredibly unlikely and it doesn't test that you really know anything. I would (and will) make a mnemonic for which are polar, basic/acidic, etc. In the AAMC BS outline it says to be able to figure out absolute config., and classify as acidic/basic, hydrophobic/hydrophilic.

 

[gettheleadout]

It's a waste of time and one of the things that I wish I had ignored. It seems that TBR cares a lot about it but AAMC would not bother to test it.

It's moderately low effort for extremely low (virtually 0) yield.

Of course, I cannot prove or support what I'm saying in any practical manner, so..

Eh, I'm taking biochem in the Fall, so I might as well.

 

[milski]

Eh, I'm taking biochem in the Fall, so I might as well.

Ahem, that's a whole different story. I'm trying to keep my senior year simple and avoid biochem but then I start liking schools which do have it as pre-req. Hard is the life of those with first world problems. 😀

On the amino acids - I detest arbitrary memorization and the disconnect between TBR and AAMC rubs me the wrong way, thus I'll use any occasional chance I get to bitch about it.

PS: If you ever find an AAMC-sourced question which can be solved by knowing the structures, let me know. I'm yet to come across one but I might have missed something.

 

[LookingForASpot]

Don't forget about proline as an important AA because it is cyclic and causes a bend in the structure... angel strain is an issue.

Also Cysteine has an SH bond

Glycine is the only one that is achiral

Then remember the classifications, polar, basic, acidic etc.

 

[medic86]

Don't forget about proline as an important AA because it is cyclic and causes a bend in the structure... angel strain is an issue.

Also Cysteine has an SH bond

Glycine is the only one that is achiral

Then remember the classifications, polar, basic, acidic etc.

Well, this entire thread is moot since the MCAT directly tests biochemistry.

You better know your amino acids for MCAT 2015.

 

[breezy16]

I would absolutely know your AAs. Even for the old test, I can attest that on both tests I have gotten questions on them without structures.

Know the R groups, how they react, think of in what terms they would react: SN or acid base chemistries. Why do they go either way? Why is it hydrophobic or hydrophilic and where would it be located on a peptide ? Inside, outside, in an active site?

Amino acid recognition will be the easiest of biochemistry and getting a jump on it will make your life easier. It's fun too, a lot of different applications.

 

[pithy84]

My real MCAT had at least 2 questions that required some knowledge of the side chains. This is a made up example with a similar type of knowledge required:

Question: Which of the following single residue substitutions is most likely to severely decrease the enzyme's activity:

A. Alanine --> lysine in the active site.

B. Leucine --> valine in the active site.

C. Alanine --> lysine in a place that doesn't matter. (See picture, see the peptide chain that hangs off the end and does nothing.)

D. Leucine --> valine in a place that doesn't matter.

You need to know two things: (1) It is not C or D because that place doesn't matter, the active site matters more. And (2) It is answer A, because alanine is small and nonpolar, and lysine is big, basic, and very polar.

As you can see, the question requires some knowledge of four different amino acids. But it is not like you need to memorize all 20 side chains. If all you remember is that lysine is basic and highly polar, you are likely to guess A and be correct. Just knowing 1 of the 4 side chains can help you skate through that question.

 

[LookingForASpot]

Thank you for the clarification. Guess I will try to at least remember a few before this Friday.

 

[slesium77]

If your going to take Biochemistry ever it won't hurt to learn the AA's. I was dredding it but I found this video online:

- it's extremely well made (there's an additional video that this should link to when you watch it) and I learned all the structures + the important pKa's very quickly. If your crunched for time you can probably use your time more wisely elsewhere but if you do have to run the AA gauntlet this is the way to go.

 

[LookingForASpot]

WOw thanks Slesium77!! 🙂