Question

I am having trouble understanding the concept of the 20 amino acids (non polar, polar, acidic, basic) and why their side chains lose or gain a proton based on pH. If anyone could explain this, that would be great!

Answer 1

I dont know what is what you want to understand about. It is not that easy as to said it is Cu because it has 29 protons in the nucleus.
You have to know something about organic chemitry and principles of pH to get some clues why an aminoacid is non polar, polar, acidic, basic. If you tell me what is your understanding about polar, acid and base I can start building from there.

Answer 2

do you know what is something defined as a polar or non polar?

Answer 3

polar amino acid

Definition: an α-amino acid in which the functional group attached to the α-carbon (R in RCH(NH3+)COO−) has hydrophilic properties, serine, cysteine, homocysteine.


hydrophilic : Tending to dissolve in water.

Answer 4

Okay, let's say that Arginine is placed into a pH of 10. How do I know which groups will be pronated and which groups will be depronated?

This is my understanding:
If the pH is > pKa, H off, depronated
if the pH is < pKa, H on, pronated

The pKa of the carboxylic acid group is about 2.3
The pKa of the amino group is about 9.7
The pKa of the R side chain is 12.5

Carboxylic acid would be depronated to COO-, because a pH of 10 > pKa of 2.3
Amino group would be depronated to NH2, because a pH of 10 > pKa of 9.7
The R side chain would be pronated, because pH of 10 < pKa of 12.5

Answer 5

I agree with you, what are your concern about?

Answer 6

I think I figured it out by myself, lol, talking through it helps. I guess I didn't know how to do it, but now that I know to look at the ionizable groups.... and look at the pKa and the pH and the relationship when if pH > pKa, a proton comes off, and if pH < pKa, a proton is on.

Answer 7

Yes you are correct, this it is the way when you have just the aminoacid in solution.
If you have the amino acid in a peptide (chain of aminoacids) "val-arg-leu" you only consider one amino and one acid group and the side chains of the 3 aminoacids. The others amino and acid group can not hydrolyze because they are in the peptidic bond

Answer 8

oooooh okay! that makes sense!!! thank you!