Proteins

Proteins

Discovered in 1838, proteins are an organic compound that makes up living organisms and are essential for life. Proteins are the macromolecules of life. Proteins have many different properties and function in a variety of ways. They function as a building structure, in teeth, bones and muscles. They also serve as enzymes, hormones, and neurotransmitters. Its functions of a protein are the most diverse of any family.

Whether found in humans, animals, or plants proteins are made of units of 20 different amino acids.(1) Proteins are made up of hundreds, thousands, or sometimes even millions of amino acids.(2) These amino acids are made up of carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur.

The most basic level of protein structure, is the linear sequence of amino acids. Different arrangements of the amino acids along a chain, affect the structure and function of a protein. Protein's secondary structure often contains long strands of amino acids that line up together and make sheets. These are called beta strands and the sheets are called beta-pleated sheets.(3) 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.(4) 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 serve is 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.(4) 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.(2)

There are two types of proteins, fibrous and globular. The major fibrous proteins are collagen, keratin, fibrinogen, and muscle proteins. Collagen, which makes up the bones, skin, tendons, and cartilage, is the most abundant protein found in vertebrates. Keratin, which makes up the outermost layer of skin and the hair, nails, and feathers of animals, twists into a regularly repeating coil called an alpha helix. Further more, fibrinogen is the blood plasma protein responsible for blood clotting. Lastly, myosin is the protein completely responsible for muscle contraction, combines with actin, another muscle protein, forming actomyosin, the different filaments of which shorten, causing the contracting action.(3)

Unlike fibrous proteins, globular proteins are spherical and highly soluble. They play a dynamic role in body metabolism. Examples are albumin, globulin, casein, hemoglobin, all of the enzymes, and protein hormones. The albumins and globulins are classes of soluble proteins abundant in animal cells, blood serum, milk, and eggs. Hemoglobin is a respiratory protein that carries oxygen throughout the body and is responsible for