The first two are simple carboxylic acids, and the third is an amino alcohol. All three compounds are soluble in organic solvents (e.g. ether) and have relatively low melting points. The carboxylic acids have pKa's near 4.5, and the conjugate acid of the amine has a pKa of 10. The simple amino acid alanine is the last entry. By contrast, it is very high melting (with decomposition), insoluble in organic solvents, and a million times weaker as an acid than ordinary carboxylic acids.
https://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/proteins.htm
For simple amino acids such as alanine, the pI is an average of the pKa's of the carboxyl (2.34) and ammonium (9.69) groups. Thus, the pI for alanine is calculated to be: (2.34 + 9.69)/2 = 6.02, the experimentally determined value.
https://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/proteins.htm
On hydrolysis they yield only the amino acids and occasional small carbohydrate compounds. Examples are: albumins, globulins, glutelins, albuminoids, histones and protamines. (b) Conjugated proteins. These are simple proteins combined with some non-protein material in the body.
http://www.fao.org/docrep/X5738E/x5738e04.htm
1. PROTEINS. Proteins are complex, organic compounds composed of many amino acids linked together through peptide bonds and cross-linked between chains by sulfhydryl bonds, hydrogen bonds and van der Waals forces.
http://www.fao.org/docrep/X5738E/x5738e04.htm
Carbohydrates are roughly 50% oxygen, and like the lipids, usually have less than 5% nitrogen (often none at all). Proteins and peptides, on the other hand, are composed of 15 to 25% nitrogen and about an equal amount of oxygen. The distinction between proteins and peptides is their size.
https://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/proteins.htm
These same fish fed diets devoid of other L-amino acids grew as well as fish receiving all 18 amino acids tested (Fig. 4). The nitrogen component in the test diets was made up of 18 L-amino acids in the pattern found in whole egg protein.
http://www.fao.org/docrep/X5738E/x5738e04.htm
The amino acids are the building blocks of proteins; about 23 amino acids have been isolated from natural proteins. Ten of these are indispensable for fish. The animal is incapable of synthesizing indispensable amino acids and must therefore obtain these from the diet.
http://www.fao.org/docrep/X5738E/x5738e04.htm
Amino acids are usually classified by the properties of their side-chain into four groups. The side-chain can make an amino acid a weak acid or a weak base, and a hydrophile if the side-chain is polar or a hydrophobe if it is nonpolar. The chemical structures of the 22 standard amino acids, along with their chemical properties, are described more fully in the article on these proteinogenic amino acids.
https://en.wikipedia.org/wiki/Amino_acid
Because all amino acids contain amine and carboxylic acid functional groups, they share amphiprotic properties. Below pH 2.2, the predominant form will have a neutral carboxylic acid group and a positive α-ammonium ion (net charge +1), and above pH 9.4, a negative carboxylate and neutral α-amino group (net charge −1).
https://en.wikipedia.org/wiki/Amino_acid
The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, though other elements are found in the side-chains of certain amino acids. About 500 amino acids are known (though only 20 appear in the genetic code) and can be classified in many ways.
https://en.wikipedia.org/wiki/Amino_acid
how many standard amino acids in protein
There are 23 standard amino acids in protein.