Amino Acids at a Glance
Amino acids are the molecular building blocks of peptides and proteins. Every standard amino acid has the same core: an alpha carbon bonded to an amino group, a carboxyl group, a hydrogen atom and a side chain (R group).
What sets one amino acid apart from another is the side chain. In glycine it is a single hydrogen atom; in tryptophan it is a bulky indole ring. Side chains can be water-loving or water-avoiding, acidic or basic. Every standard residue except glycine is chiral, and proteins are built from the L-form. For the longer explainer, read What Are Amino Acids? in the Research Library.
The 20 Standard Amino Acids
The genetic code specifies 20 standard types, and each has an internationally agreed three-letter and one-letter abbreviation [1].
| Amino acid | 3-letter | 1-letter | Side-chain class |
|---|---|---|---|
| Alanine | Ala | A | Nonpolar, aliphatic |
| Arginine | Arg | R | Positively charged |
| Asparagine | Asn | N | Polar, uncharged |
| Aspartic acid | Asp | D | Negatively charged |
| Cysteine | Cys | C | Polar, uncharged (thiol) |
| Glutamic acid | Glu | E | Negatively charged |
| Glutamine | Gln | Q | Polar, uncharged |
| Glycine | Gly | G | Nonpolar; achiral |
| Histidine | His | H | Positively charged (partly at neutral pH) |
| Isoleucine | Ile | I | Nonpolar, aliphatic |
| Leucine | Leu | L | Nonpolar, aliphatic |
| Lysine | Lys | K | Positively charged |
| Methionine | Met | M | Nonpolar (thioether) |
| Phenylalanine | Phe | F | Aromatic |
| Proline | Pro | P | Nonpolar; cyclic |
| Serine | Ser | S | Polar, uncharged |
| Threonine | Thr | T | Polar, uncharged |
| Tryptophan | Trp | W | Aromatic |
| Tyrosine | Tyr | Y | Aromatic, polar |
| Valine | Val | V | Nonpolar, aliphatic |
Some organisms also encode selenocysteine (Sec, U) and pyrrolysine (Pyl, O) by recoding stop codons [2]. Synthetic peptides can go further, using non-standard residues such as norleucine, aminoisobutyric acid (Aib) or D-amino acids, which call for extended notation.
Classifying Amino Acids by Side Chain
Chemists usually group them by side-chain chemistry. The side chain controls charge and polarity, and with them, how a residue behaves inside a peptide.
- Nonpolar, aliphatic: glycine, alanine, valine, leucine, isoleucine, methionine and proline.
- Aromatic: phenylalanine, tyrosine and tryptophan. They absorb ultraviolet light, which helps with detection in HPLC.
- Polar, uncharged: serine, threonine, cysteine, asparagine and glutamine.
- Positively charged: lysine, arginine and histidine.
- Negatively charged: aspartic acid and glutamic acid.
Nutrition science sorts them differently, into essential and nonessential groups, depending on whether the human body can make them [3]. That grouping is about biology rather than chemical structure, so the two systems overlap instead of competing.
Amino Acids and Peptides
An amino acid is one molecular unit. A peptide is two or more of these units joined in a defined order, so the two terms are not interchangeable.
Each link is a peptide bond: an amide formed between the carboxyl group of one amino acid and the amino group of the next. Once inside a chain, an amino acid is called a residue. A peptide's properties depend on more than its residue count. Which residues are present, and in what order, matters just as much. See peptide bonds and what are peptides for more.
What Is an Amino-Acid Sequence?
An amino-acid sequence is the order of residues along a peptide or protein chain, written from the N-terminus to the C-terminus in one-letter or three-letter codes.
Sequence is how researchers tell specific peptides apart. Glutathione is written gamma-Glu-Cys-Gly. GHK-Cu is built on the tripeptide Gly-His-Lys, and MOTS-c is the 16-residue sequence MRWQEMGYIFYPRKLR. Where it applies, each Vinnix compound page shows verified sequence information. For notation, including modified residues, see peptide sequences.
From Amino Acids to Peptides and Proteins
These terms describe related levels of structure, and mixing them up causes confusion. An amino acid is a single building block. A peptide is a chain of these units joined by peptide bonds. A protein is a larger folded chain, or a set of chains.
| Term | What it is | Example |
|---|---|---|
| Amino acid | Single molecular unit | Lysine |
| Dipeptide / tripeptide | Two or three linked residues | KPV (Lys-Pro-Val) |
| Peptide / polypeptide | Short to medium chain | Sermorelin, 29 residues |
| Protein | Long chain(s) with a folded 3D structure | Hundreds of residues or more |
No single chain-length cutoff separates a peptide from a protein. For a fuller comparison, read peptides vs proteins.
Why Residue Order Matters
Two chains with the same number of residues, or even the same building blocks, are different molecules if the order differs.
Change one position and a peptide's structure and chemical behavior can shift. Isomeric sequences also share the same mass, which is why you need specific compound identification and suitable analytical characterization. Used together, HPLC and mass spectrometry help confirm that a sample matches its stated sequence. Peptide testing explains how these methods are applied.
Vinnix Amino Acid Products
Vinnix amino-acid products aren't listed yet. A range is in preparation and will appear on this page at launch.
Those product pages will use the same format as the Vinnix peptide catalog: compound identity, specifications, SKU and batch information, with certificates of analysis in the COA Library. Until then, you can browse available peptides or the Compound Library.
Vinnix products are supplied for laboratory research use only and are not for human or veterinary use.
FAQFrequently asked questions
What are amino acids?
Amino acids are organic compounds in which an amino group, a carboxyl group, a hydrogen atom and a side chain all attach to a central alpha carbon. The genetic code encodes twenty standard types. Linked by peptide bonds in a defined order, they form peptides and proteins, and each side chain gives its residue a distinct chemistry.
How many standard amino acids are there?
The genetic code encodes 20 standard amino acids, from alanine to valine. Selenocysteine and pyrrolysine are sometimes counted as the 21st and 22nd, because certain organisms encode them by reinterpreting stop codons. Plenty of others exist in nature and in synthetic chemistry, but they aren't genetically encoded.
What is the difference between an amino acid and a peptide?
An amino acid is a single building block. A peptide is a chain of two or more residues joined by peptide bonds. What a peptide is depends on which residues it contains and the order they come in, so two peptides of the same length can be entirely different compounds.
What do the one-letter amino acid codes mean?
They're standardized abbreviations for the 20 standard residues, used to write sequences compactly. Some match the name, like G for glycine. Others don't, such as K for lysine and W for tryptophan. The same standard defines the three-letter codes too, for example Gly, Lys and Trp.
Does Vinnix sell amino acids?
Not yet. Vinnix amino-acid products are in preparation and will be added to this page at launch, with full specifications, SKUs, batch information and certificates of analysis. Until then, you can browse the peptide catalog and the Compound Library, which already cover the compounds we list.
REFScientific references
-
IUPAC-IUB JCBN. IUPAC-IUB Joint Commission on Biochemical Nomenclature (JCBN). Nomenclature and symbolism for amino acids and peptides. Recommendations 1983. Biochem J. 1984;219(2):345-73. PubMed 6743224
reference standard, nomenclature recommendations -
Ambrogelly A, et al. Natural expansion of the genetic code. Nat Chem Biol. 2007;3(1):29-35. PubMed 17173027
review -
Lopez MJ, et al. Biochemistry, Essential Amino Acids (Archived). In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024. NCBI Bookshelf NBK557845. PubMed 32496725
textbook chapter, NCBI Bookshelf (StatPearls)