amino acid §

The monomer of a protein.

All 20 of the common amino acids are α-amino acids (carboxyl and amino group bonded to the same carbon). This carbon is a chiral centre resulting in amino acid stereoisomers (enantiomers).

Amino acid residues in proteins are L-stereoisomers (A few exceptions), which enables the formation of stable, repeating sub-structures in proteins.

Properties of Amino Acids §

Property	Amino Acid	3 Letter Code	Symbol
Non-polar	Glycine	Gly	G
	Alanine	Ala	A
	Proline	Pro	P
	Valine	Val	V
	Leucine	Leu	L
	Isoleucine	Ile	I
	Methionine	Met	M
Aromatic	Phenylalanine	Phe	F
	Tyrosine	Tyr	Y
	Tryptophan	Trp	W
Polar	Serine	Ser	S
(Uncharged)	Threonine	Thr	T
	Cysteine	Cys	C
	Asparagine	Asn	N
	Glutamine	Gln	Q
Positive	Lysine	Lys	K
	Arginine	Arg	R
	Histidine	His	H
Negative	Aspartate	Asp	D
	Glutamate	Glu	E

• The R groups of Alanine, Valine, Leucine, and Isoleucine tend to cluster together stabilising a protein structure with the hydrophobic effect. Additionally, phenylalanine, tyrosine, and tryptophan can contribute to the hydrophobic effect, although the latter are less polar than F due to the hydroxyl group and the nitrogen of the indole ring, respectively. Glycine’s hydrogen side group does not contribute to the hydrophobic effect.
• Methionine has a slightly non-polar thioether group in its side-chain.
• Proline is a rigid structure that reduces the structural flexibility of polypeptide regions.
• Serine, threonine, cysteine, asparagine, and glutamine are more soluble in water because their functional groups form hydrogen bonds with the water. S & T, are more polar due to their hydroxyl groups, as well as N & Q because of their amide groups. C is a weak acid and only makes weak hydrogen bonds with its sulfhydryl group, however Cysteine is readily oxidised to form a covalently linked dimeric amino acid called cystine.
• Charged amino acids are the most hydrophilic and water soluble.

2021-11-14T23:32

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References §