Ch. 26 - Amino Acids, Peptides, and ProteinsSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Acid-Base Properties of Amino Acids

See all sections
Proteins and Amino Acids
L and D Amino Acids
Polar Amino Acids
Amino Acid Chart
Acid-Base Properties of Amino Acids
Isoelectric Point
Additional Practice
Amino Acid Nomenclature

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)