Need help on Neap 2010 trial exam =(

[happyhappyland]

Also, amino acids are in their acidic form when the pH is above their isoelectric point (pH at which the amino acid exists as a zwitterion) Wtf? That makes no sense. Shouldn't they be in the basic form is the pH is above their isoelectric point?

I thought zwitterion ion existed cos it just did. and they act as base in acid and acid in base.

[kenhung123]

Hmm I have a similar problem to this neap question
Since all amino acids alanine, glutamic acid and serine are of same charge in pH 6 all would contain 1 NH3+ group? So the only separating factor is the weight. Now isn't alanine lighter than serine thus move further distance to both glutamic acid and serine?

[kyzoo]

Hmm I have a similar problem to this neap question
Since all amino acids alanine, glutamic acid and serine are of same charge in pH 6 all would contain 1 NH3+ group? So the only separating factor is the weight. Now isn't alanine lighter than serine thus move further distance to both glutamic acid and serine?

They aren't of the same charge, that's where the isoelectic point data comes into play

[m@tty]

Also, amino acids are in their acidic form when the pH is above their isoelectric point (pH at which the amino acid exists as a zwitterion) Wtf? That makes no sense. Shouldn't they be in the basic form is the pH is above their isoelectric point?

If the pH is high then there are many proton acceptors, so the zwitterion will donate. You have lots of OH^-s floating around and these drag the protons from the amino acid.

[kyzoo]

Oh lololol i get it now.

It's confusing though...according to this question, an amino acid is in its acidic form NH2-CHZ-COO- when its in a basic solution >.<.

[Martoman]

Oh lololol i get it now.

It's confusing though...according to this question, an amino acid is in its acidic form NH2-CHZ-COO- when its in a basic solution >.<.

Yeah? this is normal? It acts as a buffer!

[Mao]

Hmm I have a similar problem to this neap question
Since all amino acids alanine, glutamic acid and serine are of same charge in pH 6 all would contain 1 NH3+ group? So the only separating factor is the weight. Now isn't alanine lighter than serine thus move further distance to both glutamic acid and serine?

To answer your question,

Ala in pH 6 is neutral
Glu in pH 6 is -1 (carboxyl in Z group donates)
Ser in pH 6 is neutral

[kenhung123]

Umm, so amino acids 'neutral' pH is at 6 not 7? So zwitterions are formed in pH 6, at pH<6 the amino acids act as base and pH>6 the amino acid act as an acid? Btw, I think in this question, they assumed serine lost a H from OH group forming negative charge O- so glutamic acid is behind serine. Unless they are saying the mass has a greater effect on the movement in gel than charge

[Mao]

Umm, so amino acids 'neutral' pH is at 6 not 7? So zwitterions are formed in pH 6, at pH<6 the amino acids act as base and pH>6 the amino acid act as an acid? Btw, I think in this question, they assumed serine lost a H from OH group forming negative charge O- so glutamic acid is behind serine. Unless they are saying the mass has a greater effect on the movement in gel than charge

No, the isoelectric point (neutral pH) of the amino acid group (not including the Z group) is usually around 7. A large deviation from this pH is required to change the state of the zwitterion, so to make Ala a positive ion (acid form, a H+ is forced back onto the carboxyl), a low pH (less than 3) is required.

[Blakhitman]

worst exam ever.

[Martoman]

No i think the LisaChem ones are harder.

[Akirus]

No i think the LisaChem ones are harder.

So Lisachem 2010 is even harder than the NEAP 2010 paper? I haven't done either yet, should get around to it this week.

[Martoman]

Haven't done 2010, but 09's multi choice destroyed me.

[Akirus]

Hm, that was the first trial paper I did. Multi-choice was okay other than a few careless mistakes, screwed up heaps of stuff in the short-answer though. Misinterpreted a 4-mark q >.>

[Martoman]

eh in 09 they basically make up their own new analysis and say here are the rules, now you play my game. Then a big 4 marker came out of nowhere.