Amino acids are the building blocks of proteins.
The average molecular weight of an amino acid is 135.
An amino acid with both positive and negative regions is called zwitterion. The presence of a charge on the amino acid makes the amino acid water-soluble.
The ziweitterion is the predominant formm at a particular pH, which is designed the isoelectric point(pI).
At a pH below the pI, some of the carboxylate groups are protonated.
At a pH above the isoelectric point some of the ammonium groups are deprotonated.
Chiral Amino Acids
In a typical alpha-amino acid, four different groups are attached to the alpha-carbon(-COOH, -NH3, -R, and -H).
Chiral amino acids come in two different forms: the D and the L forms. Only the L forms are constityents of natural proteins.
Magic 20 Amino Acids
- Nonpolar (hydrophobic) and uncharged
- Polar (hydrophilic) and uncharged
- Acidic (polar and charged)
- Basic (polar and charged)
Nonpolar(hydrophobic) and Uncharged Amino Aicds
- Alanine (Ala, A) 丙氨酸
- Isoleucine (Ile, I) 异亮氨酸
- Leucine (Leu, L) 亮氨酸
- Methionine (Met, M) 甲硫氨酸
- Phenylalanine (Phe, F) 苯丙氨酸
- Proline (Pro, P) 脯氨酸
- Tryptophan (Trp, W) 色氨酸
- Valine (Val, V) 缬氨酸
The amino acids alwats occur as ions. They may occur as zwitterions, cations, anions.
Polar(hydrophilic) and Uncharged Amino Acids
Amide, alcohol, and sulfhydryl groups are polar and neutral.
- Asparagine (Asn, N) 天冬酰胺
- Cysteine (Cys, C) 半胱氨酸
- Glutamine (Gln, Q) 谷氨酰胺
- Glycine (Gly, G) 甘氨酸
- Serine (Ser, S) 丝氨酸
- Threonine (Thr, T) 苏氨酸
- Tyrosine (Tyr, Y) 酪氨酸
Acid Amino Acids
The side group contains a carboxyli acid group. The secondary carboxylic acid group is a weaker acid than the primary carboxylic acid group.
- Aspartic Acid (Asp, D) 天冬氨酸
- Glutamic Acid (Glu, E) 谷氨酸
Basic Amino Acids
- Arginine (Arg, R) 精氨酸
- Histidine (His,H) 组氨酸
- Lysine (Lys, K) 赖氨酸
Rarer Amino Acids
- Amino acid may undergo modification after incorporated into a protein.
- Collagen and gelatin, proteins present in higher vertebrates, contain gtdroxylysine and hydroxyproline.
- These two amino aicds containadditional -OH group on the side chain.
- Certain amino acids do not occur in proteins.
- Cirtulline serves as a precursor of argine.
- Ornithine, homocysteine, and homoserine are important as metabolic intermediates.