Basic Structure#
Amino acid structure
Amino Acid Properties#
| Amino Acid | 3-letter / 1-letter | Unique Feature / Special Property | Biological Significance |
|---|---|---|---|
| Alanine | Ala / A | Small, chemically inert methyl side-chain. | Used as the baseline in mutation studies (Alanine scanning). |
| Arginine | Arg / R | Positively charged; contains a highly basic guanidinium group. | Forms complex salt bridges and hydrogen bond networks. |
| Asparagine ⠀ ⠀ ⠀ ⠀ ⠀ ⠀ ⠀ ⠀ ⠀ ⠀ | Asn / N | Polar carboxamide group; prone to deamidation. | Primary site for N-linked glycosylation. |
| Aspartic acid | Asp / D | Negatively charged carboxylate group; short side-chain. | Coordinates metal ions (like Mg2+) in enzyme active sites. |
| Cysteine | Cys / C | Contains a highly reactive thiol (-SH) group. | Forms disulfide bonds to stabilize tertiary/quaternary structures. |
| Glutamic acid | Glu / E | Negatively charged carboxylate group; longer side-chain. | Acts as the primary excitatory neurotransmitter in the brain. |
| Glutamine | Gln / Q | Polar carboxamide group; highly flexible. | Acts as the primary nitrogen donor in metabolic pathways. |
| Glycine | Gly / G | Smallest amino acid; hydrogen side-chain; no chiral center. | Provides high conformational flexibility in protein backbones. |
| Histidine | His / H | Imidazole ring with a pKa near physiological pH (~6.0). | Actively switches charges; vital proton donor/acceptor in enzymes. |
| Isoleucine | Ile / I | Branched-chain with two chiral centers. | Packages tightly within hydrophobic interiors. |
| Leucine | Leu / L | Branched-chain; most abundant amino acid in proteins. | Crucial for structural stability and signaling pathways. |
| Lysine | Lys / K | Positively charged; long, flexible aliphatic chain with primary amine. | Frequent target for ubiquitination and acetylation. |
| Methionine | Met / M | Thioether side-chain; contains sulfur. | Serves as the universal start codon (AUG) for translation. |
| Phenylalanine | Phe / F | Highly hydrophobic benzene ring side-chain. | Absorbs UV light; crucial for aromatic stacking. |
| Proline | Pro / P | Cyclic imino acid; side-chain bonds to nitrogen backbone. | Creates kinks or breaks in alpha-helices; rigid structure. |
| Serine | Ser / S | Polar uncharged; contains a highly reactive hydroxyl group. | Core component of catalytic triads (e.g., serine proteases). |
| Threonine | Thr / T | Polar uncharged; contains two chiral centers. | Frequent target for O-linked glycosylation. |
| Tryptophan | Trp / W | Largest amino acid; contains a bulky indole ring. | Strongest UV absorber at 280nm; precursor to serotonin. |
| Tyrosine | Tyr / Y | Amphipathic; contains a reactive hydroxyl group on a phenyl ring. | Major site for phosphorylation in cellular signaling. |
| Valine | Val / V | Branched-chain hydrocarbon; highly hydrophobic. | Stabilizes protein cores via hydrophobic interactions. |
Amino Acid Structure#
| Amino Acid | Abbrev. | Code | MW (Da) | Catagory | R-group | Codon notation |
|---|---|---|---|---|---|---|
| Alanine | Ala | A | 89 | nonpolar | $\ce{CH3}$ | GCN |
| Arginine | Arg | R | 174 | basic | $\ce{(CH2)3NH-C(NH)NH2}$ | CGN, AGR1 |
| Asparagine | Asn | N | 132 | polar | $\ce{CH2C(O)NH2}$ | AAY |
| Aspartic acid | Asp | D | 133 | acidic | $\ce{CH2C(O)OH}$ | GAY |
| Cysteine | Cys | C | 121 | polar | $\ce{CH2SH}$ | UGY |
| Glutamic acid | Glu | E | 147 | acidic | $\ce{CH2CH2C(O)OH}$ | GAR |
| Glutamine | Gln | Q | 146 | polar | $\ce{CH2CH2C(O)NH2}$ | CAR |
| Glycine | Gly | G | 75 | nonpolar | $\ce{H}$ | GGN |
| Histidine | His | H | 155 | basic | $\ce{CH2-C3H3N2}$ | CAY |
| Isoleucine | Ile | I | 131 | nonpolar | $\ce{CH(CH3)CH2CH3}$ | AUH |
| Leucine | Leu | L | 131 | nonpolar | $\ce{CH2CH(CH3)2}$ | CUN, UUR2 |
| Lysine | Lys | K | 146 | basic | $\ce{(CH2)4NH2}$ | AAR |
| Methionine | Met | M | 149 | nonpolar | $\ce{CH2CH2SCH3}$ | AUG |
| Phenylalanine | Phe | F | 165 | nonpolar | $\ce{CH2C6H5}$ | UUY |
| Proline | Pro | P | 115 | nonpolar | $\ce{CH2CH2CH2-}$ | CCN |
| Serine | Ser | S | 105 | polar | $\ce{CH2OH}$ | UCN, AGY |
| Threonine | Thr | T | 119 | polar | $\ce{CH(OH)CH3}$ | ACN |
| Tryptophan | Trp | W | 204 | nonpolar | $\ce{CH2C8H6N}$ | UGG |
| Tyrosine | Tyr | Y | 181 | polar | $\ce{CH2-C6H4OH}$ | UAY |
| Valine | Val | V | 117 | nonpolar | $\ce{CH(CH3)2}$ | GUN |
Amino Acid Structures#
Chemical structure of the 20 amino acids in the standard code
Alanine(Ala / A)
Arginine(Arg / R)
Asparagine(Asn / N)
Aspartic Acid(Asp / D)
Cysteine(Cys / C)
Glutamic acid(Glu / E)
Glutamine(Gln / Q)
Glycine(Gly / G)
Histidine(His / H)
Isoleucine(Ile / I)
Leucine(Leu / L)
Lysine(Lys / K)
Methionine(Met / M)
Phenylalanine(Phe / F)
Proline(Pro / P)
Serine(Ser / S)
Threonine(Thr / T)
Tryptophan(Tro / W)
Tyrosine(Tyr / Y)
Valine(Val / V)