Proteins can be divided into two categories: fibrous, which tend to be insoluble in water, and globular, which are more soluble in water. A protein may have up to four levels of structure. The primary...Proteins can be divided into two categories: fibrous, which tend to be insoluble in water, and globular, which are more soluble in water. A protein may have up to four levels of structure. The primary structure consists of the specific amino acid sequence. The peptide chain can form an α-helix or β-pleated sheet, which is known as secondary structure and are incorporated into the tertiary structure of the folded polypeptide. The quaternary structure describes the arrangements of subunits.
