Simple Proteins Versus Complex Proteins
In the previous topic we classified Proteins as Fibrous/Globular. Proteins can be further classified as Simple versus Complex/Conjugated. Whereas  simple proteins are made of amino acids bound together to form a large molecule, conjugated proteins are complex molecules containing simple proteins and non-protein components.
Simple proteins are made up of polypeptide chains that have no other non-protein components. When simple proteins are digested or broken down the only products are the constituent amino acids.  Some common examples of simple proteins include albumin, glutelins, albuminoids, histone proteins, and protamines. Some digestive enzymes like trypsin, chymotrypsin, and elastase are simple proteins.
Conjugated proteins are made up polypeptide chains which have both amino acids and non-protein components called prosthetic groups. These prosthetic groups are bound to the protein by what is called covalent bonds. When these proteins are digested or broken down the by-products are both amino acids and the constituent non-amino acid components. .Â
Most prosthetic groups come from vitamins. That is why it is important that our diet includes all the vitamins we need. Complex proteins can be classified according to the chemical nature of the prosthetic groups. Â
Lipoproteins contains lipid as prosthetic groups.
Glycoproteins contain sugars or carbohydrates as prosthetic groups.
Glycoproteins on cell surfaces are important for communication between cells, for maintaining cell structure and for self-recognition by the immune system.
Phosphoproteins – contains phosphate prosthetic groups.
Example: Casein is a family of related phosphoproteins found in mammalian milk. Cow’s milk: 80% of the milk protein. Human Milk: 20% and 60% of the protein. Usually exists as Calcium salt. It’s primary role is to deliver Calcium to a growing infant.
Hemoproteins – contain Heme (iron) prosthetic groups.
Hemoproteins – contain Heme (iron) prosthetic groups. Very large class of metalloproteins. The heme group confers functionality, which can include oxygen carrying, oxygen reduction, electron transfer, and other processes.
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