Organic Chemistry

Learn the toughest concepts covered in Organic Chemistry with step-by-step video tutorials and practice problems by world-class tutors.

26. Amino Acids, Peptides, and Proteins

Acid-Base Properties of Amino Acids

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Amino acids aren't always represented as neutral structures. It's time to represent them appropriately.

At physiological pH (7.4), amino acids exist as zwitterions. Let's take a deeper look.

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concept

Why Amino Acids Exist as Zwitterions

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Determining Predominant Forms

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The 7 Ionizable Amino Acids

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As mentioned, 7 of the 20 amino acids have ionizable sidechains. The 7 are:Cysteine (C), Tyrosine (Y), Aspartic Acid (D), Glutamic Acid (E), Lysine (K), Histadine (H), and Arginine (R). 

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example

Predicting Predominant Form of Lysine

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Problem

Predict the predominant form and net charge of tyrosine (Y) at pH 10. What is the net charge? 

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Problem

Determine the net charge of the dipeptide R-C at pH 4.3. (Hint:Peptide bonds do not count)