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.
Concept #1: Why Amino Acids Exist as Zwitterions
Concept #2: Determining Predominant Forms
Concept #3: The 7 Ionizable Amino Acids
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).
Example #1: Predicting Predominant Form of Lysine
Practice: Predict the predominant form and net charge of tyrosine (Y) at pH 10. What is the net charge?
Practice: Determine the net charge of the dipeptide R-C at pH 4.3. (Hint: Peptide bonds do not count)