Question

Consider the pKa values of a certain amino acid are as follows: pKa1 = 2.19, pKa2 = 9.67, pKaR = 4.25 Showing all relevant work, compute the isoelectric point of the acid. Answer:

Answer 1

Answer:

isoelectic point PI = 2.22

Explanation:

1. as the acid part of the amino acid has least Pka value hence Pka1 is for COOH group
2. and similarly the basic part i.e, NH2 has highest PKa value hence PKa2 is for NH2
3. whatever be the R group after it reaches its PKa value it looses H+ hence gains -ve charge
4. Hint: after reaching its Pka value that group looses H+ and gains a -ve charge,
5. and at an acidic ph the NH2 exists as NH3+ ( as it takes a proton from the medium )
6. to find isoelectric point u shd find the region where the charge is 0 (as in zwitterionic form net charge is 0)
7. after finding that range take average of those limits; here its range is from Pka1 to PKaR

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