Proteins

Proteins are of primary importance to the structure and function of cells. As much as 50% of the dry weight of most cells consists of proteins. Presently, over 100,000 proteins have been identified. Here are some of their many functions in animals:

1. Metabolism: Enzymes bring reactants together and thereby speed chemical reactions in cells. They are specific for one particular type of reaction and can function at body temperatures.
2. Support: Some proteins have a structural function. For exapmle, Keratin makes up hair and nails, while collagen lends support to ligaments, tendons, and skin.
3. Transport: Channel and carrier proteins in the plasma membrane allow substances to enter and exit cells. Some other proteins transport molecules in the bloood of animals; hemoglobin is a complex protein that transports oxygen.
4. Defense: Antibodies are proteins. They combine with foreign substances, called antigens. In this way, they prevent antigens from destroying cells and upsetting homeostasis.
5. Regulation: Hormones are regulatory proteins. They serve as intercellular messengers that influence the metabolism of cells. The hormone insulin regulates the content of glucose in the blood and in cells; the presence of growth hormone determines the height of an individual.
6. Motion: The contractile proteins actin and myosin allow parts of cells to move and cause muscles to contract. Muscle contraction accounts for the movement of animals from place to place. All cells contain proteins that allow cell components to move from palce to place. Without such proteins, cells would not be able to function.

Proteins are such a major part of living organisms that tissues and cells of the body can sometimes be characterized by the proteins they contain or produce. For example, muscle cells contain large amounts of actin and musoin for contraction; RBC’s(Red Blood Cells) are filled ith hemoglobin for oxygen transport; and support tissues, such as ligaments and tendons, contain the protein collagen, which is composed of tought fibres.