Cathode/Anode electrophoresis

BU Medical Sciences
This forum made possible through the generous support of SDN members, donors, and sponsors. Thank you.
FreeMeDoctor

FreeMeDoctor

Membership Revoked
Removed
10+ Year Member
15+ Year Member
Joined
Feb 18, 2007
Messages
143
Reaction score
0
Why is it that negatively charged molecules move toward the anode during electrophoresis ?

In my understanding anode means neg charged and cathode means positively charged.

What am i missing ?
Members don't see this ad.
 
FreeMeDoctor said:
Why is it that negatively charged molecules move toward the anode during electrophoresis ?

In my understanding anode means neg charged and cathode means positively charged.

What am i missing ?
Click to expand...

They dont. Negative charged molecules move towards the cathode, as predicted by Coloumb's law. Negative molecules (like DNA) move towards the + charged side of the gel.
 
Negative molecules (in electrophoresis) do not move toward the cathode. I don't know if you're running protein or nucleic acids, but these will run to the positive terminal. Just remember run to red.

Greg
 
Members don't see this ad :)
PHDMD2B said:
Negative molecules (in electrophoresis) do not move toward the cathode. I don't know if you're running protein or nucleic acids, but these will run to the positive terminal. Just remember run to red.

Greg
Click to expand...


Thanks....

What are the general rules ?

I remeber a prof saying the physics people call the anode negative and the chem people call the anode positive.

What the heck are the real rules ? why are they specific to electrophoresis ?
 
FreeMeDoctor said:
Thanks....

What are the general rules ?

I remeber a prof saying the physics people call the anode negative and the chem people call the anode positive.

What the heck are the real rules ? why are they specific to electrophoresis ?
Click to expand...

As the link above says: Conventional current flows from cathode to anode. That means that positive charges from move the cathode, to the anode.

Electron flow goes the other way. Negative charges move from the anode to the cathode.


Of course, you can just ignore the cathode/anode stuff, which is just confusing, because it changes based on what is happening, and just look at the voltages of each side.

DNA is negatively charged, and so will move in the direction of electron flow, which is from the anode, to the cathode.
 
No, that's incorrect. While electrons do indeed flow through wires from the anode to the cathode, when submerged in a solution, the anode will attract negative charges in that solution (since it is constantly losing electrons to the current and is therefore positively charged).

This is similar to an electrolytic cell, where a current of electrons moves from anode to cathode (or test charges from cathode to anode). Cations (electron poor) in solution therefore move to the cathode (electron rich), where they can be reduced by gaining electrons. Anions in solution move to the anode, where they can donate their electrons to the anode and become oxidized.



RogueNine said:
As the link above says: Conventional current flows from cathode to anode. That means that positive charges from move the cathode, to the anode.

Electron flow goes the other way. Negative charges move from the anode to the cathode.


Of course, you can just ignore the cathode/anode stuff, which is just confusing, because it changes based on what is happening, and just look at the voltages of each side.

DNA is negatively charged, and so will move in the direction of electron flow, which is from the anode, to the cathode.
Click to expand...
 
Schaden Freud said:
No, that's incorrect. While electrons do indeed flow through wires from the anode to the cathode, when submerged in a solution, the anode will attract negative charges in that solution (since it is constantly losing electrons to the current and is therefore positively charged).

This is similar to an electrolytic cell, where a current of electrons moves from anode to cathode (or test charges from cathode to anode). Cations (electron poor) in solution therefore move to the cathode (electron rich), where they can be reduced by gaining electrons. Anions in solution move to the anode, where they can donate their electrons to the anode and become oxidized.
Click to expand...


I hate electrochem. Electromagnetics is the way to go, because they dont make up confusing semantics.

Just look at the electrical field potentials.
 
it is anion to anode and cation to cathode. it's opposite or something like the two types of batteries or something i can't find my notes on how to explain this but it really is anion to anode which is different from most other systems. i think it has to do with galvanic and electrolytic??? batteries or something.
 
FreeMeDoctor said:
Why is it that negatively charged molecules move toward the anode during electrophoresis ?

In my understanding anode means neg charged and cathode means positively charged.

What am i missing ?
Click to expand...
It depends on the type of cell you use; anode can mean negative electrode in certain cells - if it's an electrochemical cell (galvanic type).....but not in an electrolytic cell.

If this is for an experiment using biomolecules, I promise you that DNA (net negative due to the phosphate backbone) migrates toward the anode (+) in DNA electrophoresis. In protein electrophoresis, SDS (net negative charge, denaturing gel) in the gel and in the boiling buffer masks any intrinsic charge in the protein and so, when denatured, the net negative charge means protein will also migrate toward the anode (+) in that cell. I've successfully performed these techniques hundreds of times to know, sadly.
 
Part of the confusion comes from the fact that the term "current" refers to the movement of positively charged molecules. So your DNA, which is negatively charged, is flowing in the opposite direction of the "current".

ie. in a battery operated electrophoresis rig:
DNA: anode-->cathode
Current: cathode-->anode
 
GreenShirt said:
Part of the confusion comes from the fact that the term "current" refers to the movement of positively charged molecules. So your DNA, which is negatively charged, is flowing in the opposite direction of the "current".

ie. in a battery operated electrophoresis rig:
DNA: anode-->cathode
Current: cathode-->anode
Click to expand...

DNA: cathode (-) --> anode (+)

DNA is negatively charged due to the phosphate groups. It will then flow to the positive anode.

The anode/cathode terms are relative to what is being studied.

However, anode = oxidation (always) and cathode = reduction (always), it just depends on whether it is a galvanic or electrolytic cell
 
FreeMeDoctor said:
Why is it that negatively charged molecules move toward the anode during electrophoresis ?

In my understanding anode means neg charged and cathode means positively charged.

What am i missing ?
Click to expand...
Anion=Negative, Anode=Positive, Cation=Positive, Cathode=negative
 
bluesTank said:
DNA: cathode (-) --> anode (+)

DNA is negatively charged due to the phosphate groups. It will then flow to the positive anode.

The anode/cathode terms are relative to what is being studied.

However, anode = oxidation (always) and cathode = reduction (always), it just depends on whether it is a galvanic or electrolytic cell
Click to expand...


this confused me too. in biology its opposite of chemistry. go figure.
 
Simple terms:

Electrophoresis is an electrolytic cell event:

Remember that in an electrolytic cell the ANODE is POSITIVE and the CATHODE is NEGATIVE.

THEREFORE, you would expect (-) to migrate towards the negative cathode.
 
You must log in or register to reply here.
Top