# Amino Acid Reference

The **20 proteinogenic amino acids** are the fundamental building blocks of all peptides and proteins.

## Hydrophobic (Non-polar)

| Amino Acid | 3-Letter | 1-Letter | Side Chain | pKa |
|------------|----------|----------|------------|-----|
| **Glycine** | Gly | G | -H | — |
| **Alanine** | Ala | A | -CH3 | — |
| **Valine** | Val | V | -CH(CH3)2 | — |
| **Leucine** | Leu | L | -CH2CH(CH3)2 | — |
| **Isoleucine** | Ile | I | -CH(CH3)CH2CH3 | — |
| **Methionine** | Met | M | -CH2CH2SCH3 | — |
| **Phenylalanine** | Phe | F | -CH2-C6H5 | — |
| **Tryptophan** | Trp | W | -CH2-indole | — |
| **Proline** | Pro | P | cyclic | — |

## Polar Uncharged

| Amino Acid | 3-Letter | 1-Letter | Side Chain pKa |
|------------|----------|----------|----------------|
| **Serine** | Ser | S | — |
| **Threonine** | Thr | T | — |
| **Cysteine** | Cys | C | 8.18 |
| **Tyrosine** | Tyr | Y | 10.07 |
| **Asparagine** | Asn | N | — |
| **Glutamine** | Gln | Q | — |

## Acidic (Negatively Charged at pH 7)

| Amino Acid | 3-Letter | 1-Letter | Side Chain pKa |
|------------|----------|----------|----------------|
| **Aspartic Acid** | Asp | D | 3.65 |
| **Glutamic Acid** | Glu | E | 4.25 |

## Basic (Positively Charged at pH 7)

| Amino Acid | 3-Letter | 1-Letter | Side Chain pKa |
|------------|----------|----------|----------------|
| **Lysine** | Lys | K | 10.53 |
| **Arginine** | Arg | R | 12.48 |
| **Histidine** | His | H | 6.00 |

See [[Peptide Science Overview]], [[Solid Phase Peptide Synthesis]]