Classification of proteins

Proteins

Simple=nonconjugated Proteins compound or conjugated p.

(they are composed only of ppc) (they have ppc and some non pro

tein groups which are called

prosthetic groups: 1. Phosphopro-

tein, 2. Lipop., 3. Met.pr.,

4. chromopr.,

The thousand proteins presented in the human body perform numerous functions too.

Dynamic function includes catalysis of chemical transformations, transport, metabolic control, and contraction. In structuralfunctions, proteins provide the matrix for bone and connective tissue, giving structure and form to the human organism.

An important class of dynamic proteins are the enzymes that catalyze chemical reactions, converting a substrate to a product at the enzyme’s active site. Almost all of the thousands of chemical reactions in living organisms require a specific enzyme catalyst to ensure that reactions occur at a rate compatible with life. The character of any cell is based on its particular chemistry, which is determined by its specific enzyme composition. Numerous genetic traits are expressed through synthesis of enzymes, which catalyze reactions that establish the phenotype. Many genetic disease results from altered levels of enzyme production or specific alterations to their amino acid sequence. Transport is another major function of proteins. For example, hemoglobin and myoglobin, which transport oxygen in blood and in muscle. Transferrin transports iron in blood. Other transport proteins bind and carry steroid hormones in blood from their site of synthesis to their site of action. Many drugs and toxic compounds are transported by proteins. Proteins participate in contractile mechanisms. Myosin and actin function in muscle contraction.

Protein have a protective role through a combination of dynamic function. Immunoglobulins and interferon are proteins that protect the body against bacterial or viral infection. Fibrin stops the loss of blood on injury to the vascular system. Many hormones are proteins or peptides. Protein hormones include insulin, thyrotropin, somatotropin (growth hormone), prolactine, luteinizing hormone, and follicle-stimulating hormone. Many polypeptide hormones have a low molecular weight (<5000) and are referred to as peptides. In general, the term protein is used for molecules composed of over 50 amino acids and peptide is used for those of less than 50 amino acids. Important peptide hormones include adrenocorticotropic hormone, antidiuretic hormone, glucagons, and calcitonin.

Proteins control and regulate gene transcription and translation. These include histones. They are closely associated with DNA, repressor and enhancer transcription factors that control gene transcription, and proteins that form a part of the heteronuclear RNA particles and ribosomes.

Structural protein function in “brick-and-mortar” roles. This include collagen and elastin, which form the matrix of bone and ligaments and provide structural strength and elasticity to organs and the vascular system. alfa-keratin occurs in hair and other epidermal tissue.

An understanding of normal functioning and pathology of the mammalian organism requires a clear understanding of the properties of proteins.