Biochemistry

Structural (supporting) proteins. This group is the largest of the proteins of living organisms. Supporting proteins are involved in the construction of the membranes of all cells. In vertebrates and humans, up to 1/3 of the total body protein is composed of muscle proteins, collagen of connective and bone tissues, keratin of hair, nails, and skin. Contractile (motor) proteins. In living nature, any form of movement (muscle work, protoplasm in the cell, cilia and flagella in unicellular organisms) is carried out by protein complexes. For example, in the process of muscle contraction and relaxation, an important role is played by specific muscle tissue proteins - actin and myosin. The molecules of these proteins are able to tightly compress and relax their structure using chemical energy accumulated in special compounds rich in energy. Transport proteins. Some proteins, such as those found in the liquid part of the blood, carry many substances through cell membranes. So, hemoglobin is a carrier of oxygen through the blood from the lungs to tissues and organs, carbon monoxide - from organs and tissues to the lungs, albumin - carriers of lipids, vitamins, metal ions, hormones. Protective proteins. In the process of evolution, living organisms have developed defense mechanisms against the influence of factors unfavorable for life. The main function of protection in humans is performed by the immune system, which provides the synthesis of specific proteins - antibodies in response to the ingestion of bacteria, toxins and other foreign substances (antigens). Antibodies are involved in the neutralization of antigens by the formation of antigen-antibody complexes. Blood coagulation, which prevents bleeding, is based on the conversion of blood proteins - fibrinogen and thrombin. The inner walls of the esophagus and stomach are lined with a protective layer of mucous proteins - mucins. Toxins of many species of organisms are also proteins (snake venoms, bacterial toxins). Digestive proteins. Enzymes released during gastrointestinal secretion are proteins (for example, amylase, pepsin, trypsin, lipase). They catalyze the breakdown of nutrients into less complex compounds. Receptor proteins. These include proteins that are able to selectively “ recognize ” and attach substances. Protein receptors of the cell membrane after binding of individual compounds transmit information inside the cell and other cells. Organoleptic is based on this mechanism (perception of various irritations by the sensory organs: smell, taste, and touch). Regulatory proteins. The action of regulatory proteins is diverse, as they are represented by various biologically active substances: hormones that are formed in the endocrine glands, mediators that are secreted in the area of nerve endings, etc. 38