Quick BS question: stand alone (Isoelectric pts)

[DieselPetrolGrl]

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Question:
If there are 3 pIs
I.e.: 5, 7, 9
And Iso-electric modeling is done on substrate of 7..then the 7 doesn?t move but ones with lower pH than 7 ------ the ones with higher ph than 7-------

a) Migrate to cathode and anode respectively
b) Migrate to anode and cathode respectively

 

[willthatsall]

b, I think

 

[DieselPetrolGrl]

thanks !
anyone else..come on now dont be shy!
i just want a trend alert im sick of trying to solve/guess/skip this! 🙁

 

[MDtoBe777]

I'm guessing B also. At pH 7, the ones with pKa lower than 7 would be positively charged. The ones that have pKa higher than 7 would be negatively charged.

So positive would move toward anode.
Negative toward cathode.

Assuming galvanic/voltaic cell..right?

 

[DieselPetrolGrl]

yes voltaic cell charge spread across...like the id method - thank you!

 

[kidgorgeous]

its b.

 

[willthatsall]

I was thinking the other way around. PI over 7 means that it will still be protonated (positive). PI under 7 means it will be deprotonated (negative). Negative moves towards the anode, positive moves toward the cathode.

 

[strangelight]

But cathode is positive in a galvanic cell, isn't it? So negative (lack of protons, therefore ph above 7) would move towards it...

 

[willthatsall]

When you are doing isoelectric focusing, the cathode is negative and the anode is positive.

 

[MDtoBe777]

are you sure? I read the opposite in TPR.

 

[willthatsall]

I PM'd you. Quote the part you read if you have time. I'm 99% sure.

 

[strangelight]

Ah, you're right about the cathode being negative & anode being positive.

But now I'm confused...wouldn't the answer be A then? B/c having a pH<7 would have a positive charge & thus migrate toward the cathode...

 

[bgreet]

Hope I don't get a question like that, I'd be completely lost.

 

[MDtoBe777]

Will is right!

Will: are there any other examples of concepts with cathode (-) and anode (+), other than the isoelectric point and the electrolytic cells?

 

[shaq786]

Will is right!

Will: are there any other examples of concepts with cathode (-) and anode (+), other than the isoelectric point and the electrolytic cells?

WILL.... How did you know that cathode is negative and anode is positive in this case?????

 

[willthatsall]

It's not a galvanic cell. It's just electrodes with a voltage source (battery) connected to them. That's why it is like an electrolytic cell.

 

[AxlxA]

When you are doing isoelectric focusing, the cathode is negative and the anode is positive.

Yep THis is right.

Think of it this way, u'r in a lab, u'r doing electrophoresis. YOU PLUG THE DAMN MACHINE INTO AN OUTLET, why? for energy of course. Hence the experiment is using a electrolytic cell and negative amino acids would move toward the positive side, which is anode.

Anode - site of oxidation, electrons are leaving here, If we need energy in our set up, then electrons are moving away from (+) field and therefore anode is positively charged.

Btw i dont get ur question disel.....

u have 3 amino acids? one at pI = 3, 7, etc?

So pI of 3 would be negatively charged and will move toward Anode.

 

[Monkey12]

Yep THis is right.

Think of it this way, u'r in a lab, u'r doing electrophoresis. YOU PLUG THE DAMN MACHINE INTO AN OUTLET, why? for energy of course. Hence the experiment is using a electrolytic cell and negative amino acids would move toward the positive side, which is anode.

Anode - site of oxidation, electrons are leaving here, If we need energy in our set up, then electrons are moving away from (+) field and therefore anode is positively charged.

Btw i dont get ur question disel.....

u have 3 amino acids? one at pI = 3, 7, etc?

So pI of 3 would be negatively charged and will move toward Anode.

Thank you...I really dont her question at all either...pH>pI depronated have a negative charge and move to the anode, pH<pI protonated and move to the cathode

 

[antissa]

if an amino acid has pI 5, that means it's neutral at pH=5
If the pH is 7 (>5), then conditions are basic for that amino acid, so it's negatively charged

 

[MDtoBe777]

One Last question..someone pleeeassee answer:

Okay, I understand everything that has been discussed in this thread. However, in an electrolytic cell aren't electrons forced to move where they do not want to go (in other words toward a negatively charged cathode). Electrons always flow from anode to cathode. Are we talking about electrons or anions/cations here or electrons? So in an both galvanic and electrolytic cells do anions flow toward the anode and the cathode? I'm confused..someone clarify..thanks 😕

 

[Monkey12]

anions always flow toward the anion...it's just that for galvanic the anions are the ones in solution...its confusing, for electrophoresis, negative charge goes to the anode, same with electrolytic, galvanic its slightly different