Biomolecules - Proteins

Proteins are the most diverse biomolecules in living organisms, performing many functions required for life. Some proteins help maintain life by regulating where and when chemical reactions in cells occur. Some proteins serve a structural function and provide internal and external support to protect and maintain cell shape. One protein called keratin is the structural protein found in the hair, skin, nails, and feathers of animals. Some proteins are involved with movement or motility. These proteins may help propel individual cells or a whole organism. Muscles in animals contain a large number of motility proteins. Another type of protein are membrane proteins that transmit signals during cell-to-cell communication, transport molecules into and out of cells, and protect living organisms by identifying and flagging invaders

The jobs of protein are so diverse because of the many unique three-dimensional structures proteins molecules form. Despite such variety, proteins also share several specific structural characteristics in their building blocks, the amino acids. There are 20 different amino acids that proteins can be built from. Amino acids are composed of carbon, hydrogen, oxygen, nitrogen and sulfur. Structural similarities among amino acids make the construction of any protein a consistent and regulated process. Each amino acid has a central carbon atom, an amino group that chemically behaves like a base and an acid group that acts as an acid chemically. The structure that make each of the 20 amino acids unique is the radical group. The radical group is a unique group of atoms bonded to the central carbon atom that give the amino acid its unique chemicla characteristics. Specific differences between each amino acids interact to create unique three-dimensional structures. Combined, the similarities and differences between amino acids explain how cells can build a diverse pool of proteins from the same set of building blocks.

When 100 or more amino acids are linked together a molecule called a polypeptide is formed. Unlike polysaccharides, polypeptide chains are assembled with a wide variety of amino acids in each chain. The set of twenty amino acids commonly found in biological proteins is directly responsible for the diversity of protein structures in living cells. Each protein has a different rearrangement of amino acids, which causes a the chain of amino acids to take on a different shape. A protein may be composed of one or more polypeptide strands. The attractions between the amino acids in the polypeptide strands cause the strands to come together to form protein molecules. A protein's structure and shape determines the function a protein can perform.

How does protein structure determine function? The three-dimensional shape of each protein is perfectly suited to perform one specific function. For example, aquaporins are proteins that form small tunnels through a cell membrane. The internal surface of aquaporin tunnels possesses a specific diameter and polarity. This structure is perfectly designed to transport water molecules but very little else, providing specificity and function. If protein structure changes, so does a protein’s ability to function.

Links to Other LHS Biomolecule Pages - Carbohydrates Lipids Nucleic Acids