BIOLOGY Volume 1 - A Guide to General Biology - 2004

3. CHEMICAL COMPONENTS OF LIVING ORGANISMS

3.5. Proteins

Proteins are constructed from Amino Acids and, consequently, their molecules invariably contain carbon, hydrogen, oxygen, and nitrogen. Some proteins also contain sulfur. Certain proteins form complexes with other molecules containing phosphorus, iron, zinc, and copper. Protein molecules—chains built from amino acids—are extremely large; they are macromolecules with molecular weights ranging from several thousand to several million. Proteins are polymers, with amino acids serving as their monomer units. Twenty different Amino acids are found in natural proteins. The potential Diversity of proteins is virtually limitless, as each protein possesses a unique Amino Acid Sequence (Chap. 23) that is genetically controlled, i.e., encoded in the DNA of The Cell that produces that specific protein. Proteins are more abundant in Cells than any other Organic compounds, accounting for over 50% of the total dry cell mass. They serve as a vital component of animal diets and can be converted within the animal body into both fat and CARBOHYDRATES. The vast diversity of proteins enables them to perform a multitude of different Functions in living organisms, ranging from structural to metabolic.

3.5.1. Sizes of protein molecules

Simple Peptides consisting of two, three, or four amino acid residues are called di-, tri-, and tetrapeptides, respectively. Chains formed by A large number of amino acid residues (up to several thousand; Table 3.6) are called Polypeptides. A protein molecule may consist of one or more polypeptide chains.

Class="center">Table 3.6. Molecular Characteristics of Some proteins