Question

17 Question (3 points) Valine is an essential amino acid, which means that it cannot be manufactured in the body and must be obtained through dietary sources. It isa branched-chain amino acid that works with the other two BCAAs (isoleucine & leucine) to promote normal growth, repair tissues, regulate blood sugar, and provide the body with energy. Correct each of the three drawings below (ie, add or remove lone pairs, charges, and atoms) to show valine at pH 1. pH 7.and pH 11. The pk, values for valine's ionizable groups are 2.29 for the -COOH group and 9.72 for the -NH3 group.

Answer 1

2 valine Iso electric point (pI) = oka, +Pkaz 2. 2049.72 2 = 6,00 completely acidic, so both NH₂,- cooh are protonated pe=1 Н 12 оон H₂ v coo Han coo At pHal At (100%) predominant at pH = 7 vollas pty pI) so pH=1 (1007)

The amino acid equilibrium depends on the pH.

NH3+ -CHR-COOH <-----> NH3+-CHR-COO- <-------> NH2CHR-COO-

monocationic pKa1 zwitterion pKa2 monoanionic form

As the pH increases, the most acidic proton is given and changes into zwitter ionic form and then at pH = pKa1 it has 50% monoctionic form and 50% zwitter ionic form .

At pH = pI the aminoacid is neutral with 100% zwitterionic for,

Then as pH > PI -COOh proton is completely lost and at pH = pKa2 , the NH3+ is lost 50% making 50% zwitterionic form and 50% monoanionic formm. When the pH is much greater than pKa2 100% monoanionic form is attained.