In addition to the important role of amino acids as precursors for protein synthesis, amino acids have important roles as intermediates in metabolism as precursors of nonpeptide compounds, such as the neurotransmitter γ-aminobutyric acid and the coenzyme nicotinamide adenine dinucleotide and as precursors for synthesis of several unique small peptides, such as glutathione.
![properties of hydrophobic amino acids properties of hydrophobic amino acids](https://researchopenworld.com/wp-content/uploads/2020/12/venn-diagram.jpg)
These proteins and peptides are synthesized using amino acids as the building blocks, much as complex carbohydrates are synthesized using sugar residues as the building blocks. The human genome contains about 23,000 protein-coding genes, and proteins make up 20% to 50% of the dry mass of the adult human body, with fat being the other major component. Proteins function as enzymes, transcription factors, binding proteins, transmembrane transporters and channels, hormones, immunoglobulins, motor proteins, receptors, structural proteins, and signaling proteins. Proteins are involved in essentially every process that takes place in cells, and these proteins have a remarkable diversity of functions. We now know that proteins, often called polypeptides, are made up of amino acid residues linked by peptide bonds. The name “protein” (from the Greek word proteios, meaning “primary”) was first given to this class of molecules in 1838 by Mulder’s associate, Jöns Jakob Berzelius.
![properties of hydrophobic amino acids properties of hydrophobic amino acids](http://hackert.cm.utexas.edu/courses/ch370/fall2013/AminoAcids/aminoa.gif)
The Dutch chemist Gerhadus Johannes Mulder carried out elemental analysis of common proteins and found that nearly all proteins had a similar empirical formula, C 400H 620N 100O 120P 1S 1, leading him to conclude that all “albuminous” compounds might be composed mainly of a single type of compound. Proteins were first recognized as a distinct class of biological molecules in the eighteenth century by Antoine Fourcroy and others, evidenced by the ability of egg whites, wheat gluten, plasma albumin, and fibrin (from clotted blood) to coagulate when treated with heat or acid. Structure, Nomenclature, and Properties of Proteins and Amino Acids