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Proteins Essay, Research Paper

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, 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, scales, hooves, 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 chiefly responsible for muscle contraction, combines with actin, another muscle protein, forming actomyosin, the different filaments of which shorten, causing the contracting action.

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 the bright red color of red blood cells. The enzymes, which are all globular proteins that combine rapidly with other substrates, are responsible for metabolism. Finally, hormones which come from the endocrine glands, do not act as enzymes. Instead they stimulate target organs that in return open and control important activities. An example would be, the rate of metabolism and the production of digestive enzymes and milk. So all these are characteristics of the two types of proteins, globular and fibrous.

All of those characteristics, nature, and distinctiveness of the proteins give each organism a unique indiuvality. The DNA sequences carried in each cell in blueprint. They are the instructions that tell the cell how to be part of an animal, plant, fungus or bacterium. The majority of genes are instructions that tell cells how to make proteins. Proteins are the active elements of cells. They aid and control the chemical reactions that make the cell work. They receive signals from outside the cell. They control the processes by which proteins are made from the instructions in the genes. They also give the cells their shape and as well as parts of the linkages that stick cells together into tissues and organs. So, the sequence of amino acids in all proteins is genetically determined by the sequence of nucleotides in cellular DNA.

So basically Proteins are basic constituents in all living organisms. They are complex molecules composed of amino acid and necessary for the chemical processes that occur in living organisms. Proteins are sometimes referred to as macromolecular polypeptides because they are very large molecules and because the amino acids of which they are composed are joined by peptide bonds. The vast majority of the proteins found in living organisms are composed of only 20 different kinds of amino acids, repeated many times and strung together in a particular order. Each type of protein has its own unique sequence of amino acids. Also each protein makes every living organism different.


1. Proteins, Lexicon Universal Encyclopedia, 1989

Volume 15, pg.576.

2. www.biotech.imcb.edu.com

3. http://www.faseb.org/protein.html

4. ?Proteins?. SceinceDaily.?2000


5. ?Proteins?. Britannica Online 2000


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