Bottom Answers Are: 2.2, 4.6, 10.5, 12.0. Select all which it would be. All amin

Question

Bottom Answers Are: 2.2, 4.6, 10.5, 12.0.

Select all which it would be.

All amino acids have two ionizable functional groups: an a-amino group (average pK_a of 9.4) and an a-carboxylic acid group (average pK_a of 2.2). Lysine also has an ionizable side chain (R group) with a pK_a of ~10.5. One of the possible ionization states of lysine is shown below. At what pH would the structure above be the predominant ionization state? pH = 2.2 The protonated form of the R group of lysine is shown in the structure above. The ratio of the charged (protonated) form to the deprotonated form depends of the pK_a of the R group and the pH of the solution. Select all the pH values at which the charged form of the R group would predominate.

Explanation / Answer

The charged form of Lysine in the given structure has all the groups completely protonated(dipositive ion).

The aminoa cids are buffers and at any point the pH is calculated by Hendersen equation.

pH = pKa + log [conjugate base]/[acid]

When [conjugate base] = [acid] , then pH = pka

Thus when the pH < or equal to average pKa1(2.2 ) the dicationic ion is predominant form.

Thus the answer is 2.2.

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