TPR electrophoresis answer wrong??

[unsung]

This is out of a passage from the In-Class Compendium.

The question is:

"Figure 3 represents the electrophoresis of three amino acids in a neutral pH, buffered solution. The identities of X, Y, and Z, are, respectively, most likely:

A. lysine, glycine, and cysteine.
B. glutamic acid, glycine, and proline.
C. proline, alanine, and cysteine.
D. glycine, alanine, and proline.

Figure 3 shows a battery hooked up to a gel matrix, with positive terminal of the battery hooked to the left side of the gel, and the negative terminal of the battery hooked up to the right side of the gel.

---(+)[ Z Y (center) X ](-)---

Z and Y are both clearly drawn left of the center of the gel toward the (+), while X is drawn right of center, toward the (-).

(the (+) is hooked up to the long end of the battery, the + end; and the (-) drawn is hooked up to the shorter end of the battery, the - end

The correct answer is A, which means that X = lysine, Y = glycine, and Z = cysteine.

I know lysine is a basic amino acid, but doesn't that mean it is negatively charged and should move toward the positive (+) terminal ??

So it seems like B should be the right answer, with X = glutamic acid, Y = glycine, Z = proline... so an acidic amino acid in a neutral pH should be + and move toward (-).


Anyone have any ideas? Thanks!! (This is passage 12, pg 68 of compendium if any of you have it.)

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Also, the isoelectric points of the amino acids are provided:

Alanine: 6.00
Cysteine: 5.07
Glutamic acid: 3.22
Glycine: 5.97
Lysine: 9.74
Proline: 6.30

If that helps.

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[iA-MD2013]

sure, lysine is a base. but it is positively charged. if something is basic, it wick a proton and become positively charged. a stronger base will tend to exist more as the positively charged state than the neutral. it has an amine. amines will pick up protons and become positively charged at ph 7. its pka is 10. positively charged aa will be X.
B is not a good choice because glutamic acid contains a negatively charged carboxylate. it will not move toward the neg charge.

 

[tncekm]

It looks right to me.

Lysine's isolectric point is pH 9.74, which means that in this situation there will be excess protons, so it will be protonated and positive.
Lys(+)

Glycine's isolectric point is 5.94, which means that in this situation there it will lose protons to the system and be negatively charged.
Gly(-)

Cysteine's isoelectric point is about 5, which means it also will lose protons and become negatively charged.
Cys(-)

Since Lysine(+) it will move toward the right of center toward the negative charge, and X is right of center.
Since Glycine(-) it will move left of center toward the positive charge, and Y is left of center.
Since Cysteine(-) it will also move left of center, and Z is left of center.

I think you're reading the graph wrong because you said:

I know lysine is a basic amino acid, but doesn't that mean it is negatively charged and should move toward the positive (+) terminal ??

And in this situation lysine (X) is actually positively charged moving toward the negative terminal on the right.