Amino Acid Reference Chart
Amino acids are the building blocks of every peptide. This reference chart covers the 20 standard amino acids with their properties, abbreviations, and roles in peptide structure and function.
Key Takeaways
- There are 20 standard amino acids grouped by their chemical properties: nonpolar, polar, and charged.
- Each amino acid has a three-letter code and a single-letter code used in sequence notation.
- Amino acid properties determine peptide structure, stability, and receptor binding capability.
- Peptide sequences are written from N-terminus (left) to C-terminus (right).
- Understanding amino acid properties helps you interpret why specific peptides have their observed biological effects.
Nonpolar (Hydrophobic) Amino Acids
Nonpolar amino acids tend to cluster together in the interior of protein structures and contribute to the overall stability of peptide conformations. They play important roles in receptor binding interactions where hydrophobic contacts are involved.
- 1.Glycine (Gly, G) - MW: 75.03 - Smallest amino acid, provides flexibility in peptide chains
- 2.Alanine (Ala, A) - MW: 89.09 - Simple nonpolar residue, common in alpha-helices
- 3.Valine (Val, V) - MW: 117.15 - Branched-chain amino acid, contributes to hydrophobic core
- 4.Leucine (Leu, L) - MW: 131.17 - Branched-chain, important for structural stability
- 5.Isoleucine (Ile, I) - MW: 131.17 - Branched-chain, similar role to leucine
- 6.Proline (Pro, P) - MW: 115.13 - Creates rigid bends in peptide chains due to cyclic structure
- 7.Phenylalanine (Phe, F) - MW: 165.19 - Aromatic ring, important for receptor interactions
- 8.Methionine (Met, M) - MW: 149.21 - Contains sulfur, often the initiating amino acid in protein synthesis
- 9.Tryptophan (Trp, W) - MW: 204.23 - Largest amino acid, important for UV absorption and fluorescence
Polar Uncharged Amino Acids
Polar amino acids without a net charge at physiological pH contribute to hydrogen bonding and solubility. They often appear on the surface of peptides where they interact with the aqueous environment.
- 1.Serine (Ser, S) - MW: 105.09 - Hydroxyl group, common phosphorylation site
- 2.Threonine (Thr, T) - MW: 119.12 - Hydroxyl group, glycosylation and phosphorylation site
- 3.Cysteine (Cys, C) - MW: 121.16 - Thiol group, forms disulfide bonds critical for peptide structure
- 4.Tyrosine (Tyr, Y) - MW: 181.19 - Aromatic with hydroxyl, important for signaling and phosphorylation
- 5.Asparagine (Asn, N) - MW: 132.12 - Amide group, common glycosylation site
- 6.Glutamine (Gln, Q) - MW: 146.15 - Amide group, important for nitrogen metabolism
Charged Amino Acids
Charged amino acids carry a positive or negative charge at physiological pH and are critical for ionic interactions, salt bridges, and electrostatic complementarity in receptor binding.
- 1.Aspartate (Asp, D) - MW: 133.10 - Negatively charged, involved in catalytic sites and ion binding
- 2.Glutamate (Glu, E) - MW: 147.13 - Negatively charged, important neurotransmitter precursor
- 3.Lysine (Lys, K) - MW: 146.19 - Positively charged, common modification site (acetylation, methylation)
- 4.Arginine (Arg, R) - MW: 174.20 - Positively charged, critical for receptor binding in many bioactive peptides
- 5.Histidine (His, H) - MW: 155.16 - Can be positive or neutral at physiological pH, important for catalysis and metal binding
Reading Peptide Sequences
Peptide sequences are written from the N-terminus (amino end) to the C-terminus (carboxyl end) using either three-letter or single-letter codes. Understanding this notation helps you read research literature and verify peptide identities.
- 1.N-terminus is always written on the left, C-terminus on the right
- 2.Three-letter code example: Gly-His-Lys-Cu (the peptide GHK-Cu)
- 3.Single-letter code example: AGCKNFFWKTFTSC (somatostatin analog)
- 4.Dashes between residues indicate peptide bonds in three-letter notation
- 5.Modifications like acetylation (Ac-), amidation (-NH2), or copper binding (-Cu) are noted at the relevant end
Frequently Asked Questions
Why do amino acid properties matter for peptide research?
The amino acid composition of a peptide determines its physical properties (solubility, stability, half-life) and its biological activity (which receptors it binds, how strongly, and what cellular responses it triggers). Understanding amino acid properties helps you predict peptide behavior, understand why certain peptides need specific storage conditions, and interpret research literature more effectively.
What are non-standard amino acids in peptide synthesis?
Non-standard amino acids are modified or synthetic amino acids not found in the standard 20. They are used in peptide design to improve stability (resistance to enzymatic degradation), enhance receptor binding, or add specific chemical functionalities. Examples include D-amino acids (mirror images of natural L-forms), norleucine, and various methylated or fluorinated amino acids. Many research peptides incorporate non-standard amino acids.
How many amino acids are in a typical research peptide?
Most research peptides contain between 5 and 40 amino acids. BPC-157 has 15 amino acids, semaglutide has 31 amino acids (modified GLP-1), and TB-500 is a fragment of 43 amino acids from thymosin beta-4. Shorter peptides (under 10 amino acids) tend to have shorter half-lives but may be easier to synthesize at high purity.