Isoelecric focusing

[Deepa100]

---

Members don't see this ad.

I am really confused about this-

Isoelectric focusing:

Isoelectric focusing, IEF, (often called electrofocusing) is a method for separating molecules which differ in their charge characteristics. For IEF of proteins, the protein mixture is subjected to an electric field in an inert support in which a stable pH gradient has previously been generated. The anode region is at a lower pH than the cathode and the pH range is chosen such that the proteins to be separated have their isoelectric points within this range. A protein which is in a pH region below its pI will be positively charged and so will migrate towards the cathode.[/COLOR
Why would a +vely charged amino acid move towards cathode which is also positive? OR is cathode negative? I always thought cathode is positive.

 

[rocuronium]

I'm pretty sure the cathode in gel electrophoresis is negative.

I have taken a few courses where different instructors have labeled the cathode positive or negative. I think there is some discrepancy in this.


Update: I just checked the Wikipedia site for cathode, and it seems to clarify this a little bit:

http://en.wikipedia.org/wiki/Cathode

 

[Deepa100]

I'm pretty sure the cathode in gel electrophoresis is negative.

I have taken a few courses where different instructors have labeled the cathode positive or negative. I think there is some discrepancy in this.


Update: I just checked the Wikipedia site for cathode, and it seems to clarify this a little bit:

http://en.wikipedia.org/wiki/Cathode

Thanks for the link, it helps.
But seriously, conceptually, this is kinda' crappy Kinda' screwed up...

 

[unsung]

I am really confused about this-

Isoelectric focusing:

Isoelectric focusing, IEF, (often called electrofocusing) is a method for separating molecules which differ in their charge characteristics. For IEF of proteins, the protein mixture is subjected to an electric field in an inert support in which a stable pH gradient has previously been generated. The anode region is at a lower pH than the cathode and the pH range is chosen such that the proteins to be separated have their isoelectric points within this range. A protein which is in a pH region below its pI will be positively charged and so will migrate towards the cathode.[/COLOR
Why would a +vely charged amino acid move towards cathode which is also positive? OR is cathode negative? I always thought cathode is positive.

It's a bit tricky, because in electrophoresis, & in this IEF thing too apparently, the cathode is the (-) charged pole that cations move toward.

Basically, for a battery, the cathode/anode is defined by the flow of charges (electrons), but a gel like in electrophoresis is essentially a capacitor, whose poles are defined by the species that travels between the poles (i.e. proteins), rather than the charges that are built up to form the poles (i.e. electrons.)

There's a good explanation here.. I had the same Q, essentially heh.
http://forums.studentdoctor.net/showthread.php?t=520487&highlight=cathode

Just remember that for gel electrophoresis/biology stuff, the cation is the pole that cations move toward (-), and it's essentially the reverse of how battery stuff is defined in physics.