easiest way to calculate net charge of amino acid

[lotanna]

ok I've no idea if my brain has lost its function, I took 2 undergrad biochem classes, and even though that was 4yrs ago, why am I having a hard time understanding this basic concept especially at non physiological pHs like pH of 11!!!
I use Lippincott

Anyone have any suggestions?

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[twinklz]

Ok, someone feel free to correct me if I'm wrong but...

First you need to know the pKa of the particular amino acid.

Below the pKa everything that could be protonated is. (charge of +1)
At the pKa you have the Zwitterion (partially protonated) (charge of 0)
Above the pKA everything is deprotonated. (charge of -1)

Again, if I'm wrong someone PLEASE tell me.

 

[tega]

get z pka of all the groups...so say a basic amino acid like arginine has 3 charged groups....dont remember the exact charges...

but lets...say the pKA is 10..for the amino, 2 for the cooh, and 12 for the functional group.

at ph of 11.....any groups with pkas below 11 will lose their protons.....and become charged (acids) or neutral (bases)

so the cooh would be negatively charged
and the amino group with PKA of 10 would be neutal

the basic functional group with a pka of 12...will keep its protons...and remain + charged.

so at a pH of 11...ARGinine should be neutral.

hope this helps....

 

[lotanna]

Thanks people, I just realized a few mins that reading does help! LOL

@Tega, whats up man , howz rotations treating u? schl isnt too bad this way just tryin to get used to this weekly exam deal we have.