20 Standard Amino Acids
**20 Standard Amino Acids – 2–3 line description:** Amino acids are the building blocks of proteins, each consisting of an amino group, a carboxyl group, a hydrogen atom, and a variable R group attached to a central carbon. Glycine (Gly) has a hydrogen R group, while Alanine (Ala) has a methyl (CH₃) R group. Both are nonpolar and have aliphatic side chains.
Glycine (Gly/G)
Nonpolar, aliphatic R Groups

Key Terms
Glycine (Gly/G)
Nonpolar, aliphatic R Groups
Alanine (Ala/A)
Nonpolar, aliphatic R Groups
Proline (Pro/P)
Nonpolar, aliphatic R Groups
Valine (Val/V)
Nonpolar, aliphatic R Groups
Leucine (Leu/L)
Nonpolar, aliphatic R Groups
Isoleucine (Ile/I)
Nonpolar, aliphatic R Groups
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| Term | Definition |
|---|---|
Glycine (Gly/G) | Nonpolar, aliphatic R Groups |
Alanine (Ala/A) | Nonpolar, aliphatic R Groups |
Proline (Pro/P) | Nonpolar, aliphatic R Groups |
Valine (Val/V) | Nonpolar, aliphatic R Groups |
Leucine (Leu/L) | Nonpolar, aliphatic R Groups |
Isoleucine (Ile/I) | Nonpolar, aliphatic R Groups |
Methionine (Met/M) | Nonpolar, aliphatic R Groups |
Phenylalanine (Phe/F) | Aromatic R groups |
Tyrosine (Tyr/Y) | Aromatic R groups |
Tryptophan (Trp/W) | Aromatic R groups |
Serine (Ser/S) | Polar, uncharged R groups |
Threonine (Thr/T) | Polar, uncharged R groups |
Cysteine (Cys/C) | Polar, uncharged R groups |
Asparagine (Asn/N) | Polar, uncharged R groups |
Glutamine (Gln/Q) | Polar, uncharged R groups |
Lysine (Lys/K) | Positively charged R groups |
Arginine (Arg/R) | Positively charged R groups |
Histidine (His/H) | Positively charged R groups |
Aspartate (Asp/D) | Negatively charged R groups |
Glutamate (Glu/E) | Negatively charged R groups |