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6 Categories of Proteins

Oct 6, 2011 | By Winston Kennedy

Proteins are complex structures made out of chains of amino acids bonded together by peptides. They are present in all human and animal cells and play a variety of different roles to enable their survival. Classification of proteins may be made on the basis of chemical composition, polypeptide chain size, composition elements and biological function. Classification according to their biological functions may yield the following six categories.

Structural Proteins

According to Sigma-aldrich.com, structural proteins are the most abundant of all protein classes. They help maintain the shape and structure of the cells and organs. Examples include keratin, collagen, actin and myosin. Keratin is present in the hair, skin, nails, claws, hooves and horns of animals. Collagen is present in bones, arteries and skin, while actin and myosin are present in muscle tissue.

Transport Proteins

Transport proteins, also referred to as carrier molecules, play the role of providing sites on which various substances can bond to enable transportation to other areas of the body. Examples include cytochromes, responsible for the transport of electrons, hemoglobin and myoglobin, responsible for the transport of oxygen from the lungs to the rest of the body and in the muscles respectively.

Enzymes

Enzymes are proteins that the body uses to catalyze the rate of chemical and biological processes occurring in the body. They reduce the activation energy required to initiate a reaction in the body thus speeding it up. Examples of enzymes include amylase, which helps convert starch to maltose and pepsin responsible for the breakdown of proteins to polypeptides.

Hormones

Hormones are proteins produced by the endocrine glands responsible for regulating various body processes in humans and animals. According to MedlinePlus.com, hormones influence growth and development, metabolism, sexual function, reproduction and mood. Examples include insulin, which plays a major role in the regulation of blood-sugar in the body, and somatotropin, which is essential for human skeletal growth.

Antibodies

Antibodies are proteins produced by the body in response to the detection of antigens, such as bacteria, fungi, viruses and parasites. Antibodies execute this function by bonding to the antigens to neutralize them or by clumping the antigens together to enable their removal from the system or by activating complementing proteins to destroy the antigens.

Motor Proteins

These are proteins responsible for the conversion of chemical energy in cells to mechanical energy to enable motion. Actin and myosin interactions in the muscles cause muscle contraction and relaxation in the body. A nerve impulse causes the separation of myosin from actin and vice versa, and this change in structure of the myosin head causes the muscle contraction.

References

Article reviewed by Craig Gaines Last updated on: Oct 6, 2011

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