Proteins are the macromolecules of life. Discovered in 1838, proteins are recognized as a large number of superior organic compounds that make up living organisms and are essential to their functioning. The term protein comes from the Greek word “proteies” or “primary”. Proteins have many different properties and function in a variety of ways.
They can function as a building material, in teeth, bones and muscles, and they can serve as enzymes, hormones, and neurotransmitters. Its functions are the most diverse of any family.
Whether found in humans, animals, plants or in single-celled bacteria, proteins are made of units of 20 different amino acids. Proteins consist of macromolecules called polypeptides, made from monomers called amino acids. Proteins have hundreds, thousands, or sometimes even millions of these amino acids. These amino acids are made up of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Some proteins consist of only single polypeptides. In most cases it involves two or more combined polypeptides, sometimes with other small organic molecules or metal ions.
The most basic level of protein structure, called the primary structure, is the linear sequence of amino acids. Different sequences of the acids along a chain, however, affect the structure of a protein molecule in different ways. Protein’s secondary structure often contains long stretched out chains of amino acids called strands that line up together to make sheets. These are called beta strands and the sheets are called beta-pleated sheets. A protein may contain either or both alpha helices and beta pleated sheets. Alpha helices and beta pleated sheets are joined by less clear structures often grouped together under the name of coil. Some small proteins may be made of coil.
Shape is also important. Proteins are coiled and twisted, giving it a unique shape. The shape depends on the sequence of the amino acids, which can be hydrophilic or hydrophobic. Those that are hydrophilic want contact with water and will be twisted to maximize contact. Those that are hydrophobic are twisted in such a way to minimize contact. Changing one amino acid in the polypeptide sequence can destroy this shape and make the protein function improperly if not at all.
A very important function that proteins can serve are to act as catalysts. Enzymes are organic catalysts made of proteins. They speed up reactions inside an organism. The molecule, which an enzyme catalyzes, is called a substrate. Enzymes can only act on the substrate that they were designed for. This is again because of protein shape. If the substrate molecule's shape matches the enzyme's active site, it undergoes the reaction specified. Enzymes can either break or put together substrates. They can even enhance the rate of reactions to over half-a-million molecules per second.
There are two types of proteins, fibrous and globular. The major fibrous proteins are collagen, keratin, fibrinogen,...