MBIO 2700 / Topic 4b: Zwitterions

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10 Terms

1
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What is a zwitterion?

Molecule w/ positive + negative charges but net neutral.

2
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The zwitterion can act as both an ____ and ____.

The zwitterion can act as both an acid and base.

3
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What’s the approximate pKa range of the carboxyl group and amino group?

  • Carboxyl: 1.7 to 2.6 (median is 2.2).

  • Amino: 8.9 to 10.8 (median is 9.5).

4
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What is the isoelectric point (pI)?

The pH when zwitterionic form predominates.

5
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By changing the pH by ______ protons or _______ protons to create more ___ or ___, respectively, the overall _____ on the amino acid can be changed.

By changing the pH by adding protons or removing protons to create more acid or base, respectively, the overall charge on the amino acid can be changed.

6
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Outside the optimal pH range, structures of amino acids and thus proteins may not perform efficiently or at all because they have the _______ structure due to _____ difference stemming from __ change.

Outside the optimal pH range, structures of amino acids and thus proteins may not perform efficiently or at all because they have the incorrect structure due to charge difference stemming from pH change.

7
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True or false: Amino acids with no ionizable R group will have very different titration curves from each other.

False. Amino acids with no ionizable R group will have similar titration curves.

8
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  • If you add acid to a solution with an amino acid with multiple ionizable groups, which will get protonated first? Then which next?

  • If you add base to a solution with an amino acid with multiple ionizable groups, which will get deprotonated first? Then which next?

  • If you add acid, the most basic group with the highest pKa gets it, then the next most basic, then the next, and so on.

  • If you add base, the most acidic group with the lowest pKa gets it, then the next most acidic, then the next, and so on.

9
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If you have two ionizable groups that have similar pKa’s, what would you expect on a titration curve?

There would be a merged line.

10
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For an amino acid with no ionizable R group, only containing the two ionizable alpha groups, what would the pI equal?

pI = pKa1 + pKa2 / 2.