Anodes and Cathodes and Electrophoresis

[Omni]

Kinda confused on something:
Reduction always at Cathode (Red Cat)
Oxidation always at Anode (An OX)

For Galvanic Cell, Anodes are negative
For Electrolytic Cells, Anodes are Positive

If we look at electrophoresis it can be said that the whole gel setup is like an electrolytic cell, so the cathode is negative and anode is positive. Since the acidic amino acids (those with a low pI) move towards the anode, are we to conclude that positively charged ions or molecules move towards the positive end?
I'm really confused here. Please help.

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[Vince86]

First thing is opposites always attract opposite charges. So positively charge species will move towards the negatively charged electrode which is in the case of a electrolytic cell; the cathode.

The reason why they are switched is because of the battery source. The positive end of the battery is hooked up to the anode while the cathode is to the negative end. So the attraction is due to the charge of the electrode and not the type of electrode (anode or cathode). Electrons still move from anode to cathode. But remember that current is always opposite to the electron movement.

 

[Vince86]

Your mixing two different electrophoresis's i think. The one that deals with SDS-Gel, breaks up all the proteins into negative charges. Thus it migrates to the positively charged anode; separating through mass/charge - since they all have the same neg charge they separate by mass. So larger MW = slower = doesn't travel as far.

For the Pi isoelectric focusing - its a 2d electrophoresis i think. Where you have some sort of pH gradient in the cell. So when you drop a Protein with Pi 2.0; any pH it encounters less that 2 will cause it to have a positive charge; since the amino acid would look like this NH3(+)-CHR-COOH (this will move towards the negatively charged cathode) . R denotes the side group. Anything above a ph of 2 will have a net negative which is NH2-CHR-COO(-) (this will move towards the positively charged anode). So you separate the amino acid through these ph gradients so accurately that you can separate amino acids that differ by 1 charge.

So if you want to separate 2 different proteins with Pi say 2.0 and 6.0. Put it in a ph of 4 (something inbetween); so that one of them will be above the PI and the other below so that one of them will be positively and negatively charged. There they travel to two different electrodes thus separating them.

hope it helps. gl

 

[Omni]

That really helps!
Thanks a lot!

 

[DeathandTaxes]

Bump! Can someone clarify to me how in electrophoresis, the anode becomes positive?

I always thought anodes are supposed to be negative.