Structures of Amino Acids Selenocysteine and pyrrolysine are amino acids found in some organisms CH HSe H3N H H3N Selenocysteine Pyrrolysine
Selenocysteine and pyrrolysine are amino acids found in some organisms Structures of Amino Acids
Structures of Amino Acids More than 700 nonprotein amino acids are found in nature y-Aminobutyric acid(GABA)is found in the brain and acts as a neurotransmitter Homocysteine is found in blood and is linked to coronary heart disease Thyroxine is found in the thyroid gland,where it acts as a hormone H3 HS y-Aminobutyric Homocysteine Thyroxine acid Cengage Loarring All Pights Reerved
More than 700 nonprotein amino acids are found in nature ▪ g-Aminobutyric acid (GABA) is found in the brain and acts as a neurotransmitter ▪ Homocysteine is found in blood and is linked to coronary heart disease ▪ Thyroxine is found in the thyroid gland, where it acts as a hormone Structures of Amino Acids
Structures of Amino Acids a Carbons of amino acids are chirality centers,except for glycine,H2NCH2CO2H Nature uses only one enantiomer to build proteins Often referred to as L amino acids The nonnaturally occurring enantiomers are called the D amino acids c02 C02 C02 C02 C-H HOCH2 HSCH2C-H HaC-C-H H3N-C-H H3N* H3N* H3N+ H3C L-Serine L-Cysteine L-Alanine D-Alanine (S)-Serine (R)-Cysteine (S)-Alanine (R)-Alanine
a Carbons of amino acids are chirality centers, except for glycine, H2NCH2CO2H ▪ Nature uses only one enantiomer to build proteins ▪ Often referred to as L amino acids ▪ The nonnaturally occurring enantiomers are called the D amino acids Structures of Amino Acids
Structures of Amino Acids The 20 common amino acids can be acidic,basic,or neutral, depending on their side chains -2(aspartic acid and glutamic acid)of the 20 have an extra carboxylic acid function in their side chains 3(lysine,arginine,and histidine)have basic amino groups in their side chains 15 have neutral side chains -Cysteine,a thiol,and tyrosine,a phenol,have weakly acidic side chains that can be deprotonated in a sufficiently basic solution
The 20 common amino acids can be acidic, basic, or neutral, depending on their side chains ▪ 2 (aspartic acid and glutamic acid) of the 20 have an extra carboxylic acid function in their side chains ▪ 3 (lysine, arginine, and histidine) have basic amino groups in their side chains ▪ 15 have neutral side chains ▪ Cysteine, a thiol, and tyrosine, a phenol, have weakly acidic side chains that can be deprotonated in a sufficiently basic solution Structures of Amino Acids
Structures of Amino Acids At physiological pH 7.3 within cells: The side-chain carboxyl groups of aspartic acid and glutamic acid are deprotonated The basic side-chain nitrogens of lysine and arginine are protonated Histidine contains a heterocyclic imidazole ring in its side chain and is not basic enough to be protonated Only the pyridine-like nitrogen is basic The pyrrole-like nitrogen is nonbasic because its lone pair of electrons is part of the 6z electron aromatic imidazole ring Basic; pyridine-like 0 Basic CH2CHCO Nonbasic; NH3+ pyrrole-like Imidazole ring Nonbasic Histidine
At physiological pH 7.3 within cells: ▪ The side-chain carboxyl groups of aspartic acid and glutamic acid are deprotonated ▪ The basic side-chain nitrogens of lysine and arginine are protonated ▪ Histidine contains a heterocyclic imidazole ring in its side chain and is not basic enough to be protonated ▪ Only the pyridine-like nitrogen is basic ▪ The pyrrole-like nitrogen is nonbasic because its lone pair of electrons is part of the 6p electron aromatic imidazole ring Structures of Amino Acids