The order in which the amino acids are joined and how they are branched effects the structure and of course the chemical properties of the protein. Generally the amino acids are grouped according to their side chains. Due to the fact that there are charges in the protein molecules, the overall pH of their environment must be kept in mind. Also remember that the net charge on individual proteins differs because they are composed of different amino acid combinations. A peptide bond is when the amino group of one amino acid reacts with the carboxyl group of another amino acid.
Isoelectric point is that point where there is zero net charge on the protein.
Without the net charge to cause repelling, the proteins touch, clump or aggregate, and ultimately can precipitate. Protein solubilty can be increased to a degree by adding ions of neutral salts. If the ions of neutral salts are added in excess, the proteins will precipitate. Ethanol will generally cause proteins to precipitate. This must be considered when preparing alcoholic beverages.