- Central alpha-carbon (Cα) connected to:
- Amino group (H₂N–)
- Carboxyl group (–COOH)
- Side chain (R group) unique to each amino acid
- Hydrogen atom
Key:
NH₂ = amino group
COOH = carboxyl group
R = side chain (described explicitly)
Bonds shown as “–” (single) or “=” (double)
1. Alanine (Ala, A) — C₃H₇NO₂
H
|
NH2–C–COOH
|
CH3
2. Arginine (Arg, R) — C₆H₁₄N₄O₂
H
|
NH2–C–COOH
|
CH2–CH2–CH2–NH–C(=NH)–NH2
3. Asparagine (Asn, N) — C₄H₈N₂O₃
H
|
NH2–C–COOH
|
CH2–C(=O)–NH2
4. Aspartic Acid (Asp, D) — C₄H₇NO₄
H
|
NH2–C–COOH
|
CH2–COOH
5. Cysteine (Cys, C) — C₃H₇NO₂S
H
|
NH2–C–COOH
|
CH2–SH
6. Glutamic Acid (Glu, E) — C₅H₉NO₄
H
|
NH2–C–COOH
|
CH2–CH2–COOH
7. Glutamine (Gln, Q) — C₅H₁₀N₂O₃
H
|
NH2–C–COOH
|
CH2–CH2–C(=O)–NH2
8. Glycine (Gly, G) — C₂H₅NO₂
H
|
NH2–C–COOH
|
H
9. Histidine (His, H) — C₆H₉N₃O₂
H
|
NH2–C–COOH
|
CH2–(imidazole ring)
/N\
| |
C C–NH
\\ //
N
10. Isoleucine (Ile, I) — C₆H₁₃NO₂
H
|
NH2–C–COOH
|
CH–CH3
|
CH2–CH3
11. Leucine (Leu, L) — C₆H₁₃NO₂
H
|
NH2–C–COOH
|
CH2–CH–CH3
|
CH3
12. Lysine (Lys, K) — C₆H₁₄N₂O₂
H
|
NH2–C–COOH
|
CH2–CH2–CH2–CH2–NH2
13. Methionine (Met, M) — C₅H₁₁NO₂S
H
|
NH2–C–COOH
|
CH2–CH2–S–CH3
14. Phenylalanine (Phe, F) — C₉H₁₁NO₂
H
|
NH2–C–COOH
|
CH2–(benzene ring)
15. Proline (Pro, P) — C₅H₉NO₂
H
|
NH–C–COOH
\ |
CH2–CH2–CH2
\________/
16. Serine (Ser, S) — C₃H₇NO₃
H
|
NH2–C–COOH
|
CH2–OH
17. Threonine (Thr, T) — C₄H₉NO₃
H
|
NH2–C–COOH
|
CH(OH)–CH3
18. Tryptophan (Trp, W) — C₁₁H₁₂N₂O₂
H
|
NH2–C–COOH
|
CH2–(indole ring)
/N\
| |
C C
\\ //
C
19. Tyrosine (Tyr, Y) — C₉H₁₁NO₃
H
|
NH2–C–COOH
|
CH2–(benzene ring–OH)
20. Valine (Val, V) — C₅H₁₁NO₂
H
|
NH2–C–COOH
|
CH–CH3
|
CH3
Non-standard Amino Acids Found in Nature
21. Selenocysteine (Sec, U) — C₃H₇NO₂Se
H
|
NH2–C–COOH
|
CH2–SeH
- Incorporated at UGA codons with SECIS element.
- “21st amino acid” — similar to cysteine but with selenium instead of sulfur.
22. Pyrrolysine (Pyl, O) — C₁₂H₂₁N₃O₃
H
|
NH2–C–COOH
|
CH2–(pyrroline ring with lysine chain)
- Found in certain methanogenic archaea and bacteria.
- Encoded by UAG stop codon in special contexts.
Amino Acids – SolveForce Communications