Gel elctrophoresis amino acids.

[sam0001]

Gutamic acid, serine, alanine and Arginine were anlaysed at a ph 7, in gel electophoresis. Which Amin acid would be expected to migrate the furthest towards the positive terminal?

And speaking of which, does anyone get Neap 2010, the question with gel elctophoresis?

[diligent18]

Glutamic acid, because at a pH of 7, all the amino acids will be zwitterions.  Glutamic acid would be more negative than the other amino acids due to the COO- in the side chain. So it will be the most attracted to the positive terminal and will travel further? I don't know if that's correct.

[charmanderp]

The side chain would not be deprotonated or protonated at a pH of 7. The whole point of a zwitterion is that it has a neutral overall charge.

I think what would differentiate them would be their relative molecular masses.

[oneoneoneone]

Glutamic Acid's isoelectric point would be below 7 though (closer to 4ish) because of the acidic side chain. So at pH 7 it would have a -1 net charge.

[aznxD]

Glutamic Acid has a KPa ~4.1 so the side group would be deprotonated at a pH of 7, giving it an overall negative charge.

[jasoN-]

Uhh at pH 7, the term zwitterion is loosely used for all amino acids.
For amino acids, the C- and N- terminals will be ionised (hence why in all neutral-side chain amino acids, they'll be zwitterions)
In the case of amino acids with ionisable side chains (glutamic acid, aspartic acid, lysine, histidine, arginine), the net charge depends on the pH environment.
Glutamic acid will have an ionised side group (COO-) at pH 7 and will have a net charge of -1, hence it will repel the furthest away from the negative anode (i.e. closer to positive).

Edit: zwitterions only truly occur at the isoelectric point for amino acids (you don't need to know, but the isoelectric point occurs when the amino acid ceases to migrate in a pH gradient.)
For example, glutamic acid has an isoelectric point of about 3.22, that means that the overall charge will be 0 at a pH of 3.22

[Destiny]

Wait is the side chain charged or not charged at pH=7?  I'm getting confused, are you guys contradicting each other?

[sam0001]

Lol, I have been trying to make sense of neap 2010 for about two weeks now. It just isn't clicking. I don't understand how serine could migrate further than glutamic acid??

[charmanderp]

Uhh at pH 7, the term zwitterion is loosely used for all amino acids.
For amino acids, the C- and N- terminals will be ionised (hence why in all neutral-side chain amino acids, they'll be zwitterions)
In the case of amino acids with ionisable side chains (glutamic acid, aspartic acid, lysine, histidine, arginine), the net charge depends on the pH environment.
Glutamic acid will have an ionised side group (COO-) at pH 7 and will have a net charge of -1, hence it will repel the furthest away from the negative anode (i.e. closer to positive).

Edit: zwitterions only truly occur at the isoelectric point for amino acids (you don't need to know, but the isoelectric point occurs when the amino acid ceases to migrate in a pH gradient.)
For example, glutamic acid has an isoelectric point of about 3.22, that means that the overall charge will be 0 at a pH of 3.22

Fair enough. This guy is most probably right, although I don't think that VCAA would then ask such a question given that we're told as part of the VCE Chemistry course that all amino acids are in their zwitterion state at pH of 7.

[remo14]

don't forgot to factor in molar mass! Logically the amino acid with the lowest m/c ratio should migrate the most. Its sort of like mass spectroscopy.

[sam0001]

Yeah but what I don't get with neap 2010 is the fact that glutamic acid has a greater negative charge at a ph of 6 then serine, but serine migrates further?

[AllAboutTheLGs]

It has something to do with the isoelectric points given in that  table

[diligent18]

The side chain would not be deprotonated or protonated at a pH of 7. The whole point of a zwitterion is that it has a neutral overall charge.

I think what would differentiate them would be their relative molecular masses.

If it were based on their relative molecular masses alone then alanine should be closest to the positive electrode, which, according to answer, is incorrect. 
Also, the pH does affect the side chain.  (I've done enough practice exams with similar questions to know).
I also think that there is a high chance that a question like this may be in the exam this year.  The difficulty of the VCAA exams have been increasing year by year and they will be looking for something tricky like this to separate the excellent from the good students.
I'll probably call my Chemistry teacher now and see what he has to say about this question.
Edit: I get it now.

[charmanderp]

It has something to do with the isoelectric points given in that  table

What table?

[diligent18]

It has something to do with the isoelectric points given in that  table

What table?

It's on the other side of the page for that question.