Ch. 26 - Amino Acids, Peptides, and ProteinsWorksheetSee 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

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)