MCAT ? of the day 2/22/11

[Ginger Ale]

I was under the impression that IEF sorted proteins based solely on pH, and two-dimensional gel electrophoresis combined both IEF and SDS PAGE. Therefore, for two-gel, one can figure out the difference in MW of proteins.
Is the right answer to this ? implying that IEF can differentiate proteins by MW?


Here's the ?:




The right answer is C


Half-Passage: Isoelectric focussing (IEF) is a technique used to separate molecules (mostly proteins) on the basis of their isoelectric pH. The isoelectric pH of a molecule is the pH at which it carries a net charge of zero. In IEF, a medium is setup with a pH gradient and an electric current such that there is a positively charged end and negatively charged end.

Question 2: Suppose that two different proteins have the same isoelectric pH of 2. At neutral pH, both proteins are equally negatively charged. One of the proteins has a mass of 48000 g/mol, while the other only has a mass of 10000 g/mol. Using the diagram below, if both proteins were in a mixture and were spotted at point C, then what would be the relative locations of the two proteins be partway through the isoelectric focussing separation process?

(a) The heavier protein would be at C and the lighter protein at B
(b) The heavier protein would be at D and the lighter protein at A
(c) The heavier protein would be at B and the lighter protein at A
(d) Both proteins would be at A

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[tttgo]

That seems to be what the question is implying. It makes sense that the lighter one moves faster. maybe the idea of separating only by pH and charge applies after it stops moving. At that point, mw doesn't matter. However, in this question, you're looking at it halfway.

 

[Ginger Ale]

That seems to be what the question is implying. It makes sense that the lighter one moves faster. maybe the idea of separating only by pH and charge applies after it stops moving. At that point, mw doesn't matter. However, in this question, you're looking at it halfway.

I see, it's because its partially complete...ahhh makes sense!
Thank you!