BIOLOGY
PROTEINS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Most of the carboxyl groups are dissociated and most of the amino groups bind O2
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Most of the carboxyl groups are dissociated
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Most of the carboxyl groups are dissociated create anion NH3-
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Most of the carboxyl groups are dissociated, create anion COO-and most of the amino groups bind H+ creating cation-NH3+
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Detailed explanation-1: -If an acid with a pKa lower than 7 (like a carboxylic acid, pKa 5) is dissolved in such a solution, it is the stronger acid and will transfer a proton to the solution and become the carboxylate ion. Thus when the pH is maintained at 7, carboxylic acids are ionized.
Detailed explanation-2: -Under physiological conditions (pH 7.4) in proteins the side chain usually occurs as the negatively charged aspartate form, −COO−. It is a non-essential amino acid in humans, meaning the body can synthesize it as needed.
Detailed explanation-3: –The pKa of the carboxyl group is always lower than that of the amino group hence when pH increases, the carboxyl group will be deprotonated before the amino group.-The pKb values for amino groups are lower than that of carboxyl groups, hence the amino groups will be protonated before the carboxyl groups.
Detailed explanation-4: -At high pH, both the carboxyl and amine groups are deprotonated. At these pH values, the amino acid carries a net negative charge, and is dibasic. At some intermediate pH, the amino acid is a zwitterions, and carries no net charge. This is called the isoelectric point of the amino acids, and is designated pHI.