The pKa values for the three ionizable groups on tyrosine are pKa

[lha08]

Homework Statement

The pKa values for the three ionizable groups on tyrosine are pKa (--COOH)=2.2, pKa (--NH3+)=9.11, and pKa (R)=10.07. In which pH ranges will this amino acid have the greatest buffering capacity?
A) At all pH's between 2.2 and 10.07
B) At pH's near 7.1
C) At pH's between 9 and 10
D) At pH's near 5.7

Homework Equations

The Attempt at a Solution

so basically i know that the answer is not A and can't be B since that's the answer for the isoelectric point...so that leaves b and C...like the answer is C but i just don't see how that is...we have 3 pKa values and all of them should individually act as a good buffering capacity but how am i suppose to incorporate all three values and turn it into a range?

 

[Borek]

Two approaches possible, hard and serious: buffer capacity calculation and simple and more hand wavy - reasonable buffering capacity is at pH = pKa plus/minus 1 (think how the buffer works - you need reasonable amount of both acid and conjugate base present).

--