Question

Suppose that you have an amino acid with three dissociated groups (a-carboxyl group, a-amino group and basic R-group), with the Pkas 3, 9, and 11.

B. What is the PI
C. What is the net charge at pH 6

Answer 1

B. pI=10

C. Charge 1+

Step-by-step explanation:

B. You'll write your pKa values from low to high, we'll build a table to find the charges for your three posible dissociated groups:

-COOH -NH3 -R Total charge

0 + + 2+

pH 3 -----------------------------------------------------

- + + 1+

pH 9------------------------------------------------------

- 0 + 0

pH 11------------------------------------------------------

- 0 0 1-

To calculate pI we'll take the pKa values where you have total charge zero (pKa 9 and 11):

`pI= (9+11)/(2) =10`

Our pI=10

C. considering pH 6 is between pH3 and pH9 we can assume that the net charge in that pH will be 1+.

I hope you find this information useful! Good luck!