which three of the which three of the which three of the on 8 of 35 Sapling Lear
ID: 186212 • Letter: W
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which three of the which three of the which three of the on 8 of 35 Sapling Learning macmilan learning All amino acids have two ionizable functional groups: an -amino group (average pKa of 9.4) and an carboxylic acid group (average pKa of 2.2). Histidine also has an ionizable side chain (R group) with a pKa of-6.0. One of the possible ionization states of histidine is shown below. H3N CH-C OH CH2 NH At what pH would the above structure be the predominant ionization state? Note: Consider the ionization state of all three of the functional groups PH1.5 Scroll down for mor of this question. The protonated form of the R group of histidine is shown in the structure above. The ratio of the charged (protonated) form to the deprotonated form depends of the pK, of the R group and the pH of the solution. Select the pH values at which the charged form of the R group would predominate. Hint O Previous G ve Up & Vierw Soittion e, Check Answer 0 Next ExExplanation / Answer
1. 1.5
Histidine has net charge +2 at pH below 2.2. Because below pKa 2.2 there is no change in the amino acid structure and also the carboxyl group has 'H' (COOH). If it cross the pKa-2.2 the COOH releases H+ and becomes -ve charge. So pH greater that pKa-2.2 the net charge is 1.
2. At pH 4 the R group of Histidine is always has charge.
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