Biochemistry

CHAPTER 6. LIPIDS CHEMISTRY 6.1. BIOLOGICAL ROLE, STRUCTURE AND PROPERTIES OF LIPIDS AND THEIR DERIVATIVES Lipids (from the Greek lipos - fat) - a group of diverse in composition water-insoluble organic substances that differ in varying degrees of solubility in organic solvents. Lipids are derivatives of higher fatty acids, alcohols and aldehydes. They are widely represented in the tissues of humans, animals, plants and microorganisms. The vegetative parts of plants accumulate no more than 5% lipids, seeds - 50% or more. In human tissues, the amount of lipids varies dramatically. So, in the human body normally contains 10-20 % offal, but with some violations of fat metabolism, its amount can increase up to 50%. Lipids are part of all organs and tissues. Most of them (up to 90%) are in adipose tissue. Lipids make up about half the brain mass. Lipids perform a variety of functions. Energy. These substances are a source of energy : when 1 g of fat is oxidized in the body, 9 kcal is released. So, due to fats, 25 - 35% of the daily energy requirement is provided for residents of middle latitudes, and among northerners their share in the energy supply of the diet is even greater. Regulatory. Lipids are important factors in regulating the water exchange in the body . The amount of water generated in the body during complete degradation of fats is quite large: when oxidizing 100 g of fat, 107 g of endogenous water is released, which is of particular importance in extreme conditions (for example, with insufficient intake of water from the outside). Plastic Lipids play a structural and plastic role, since they are part of the cellular and extracellular membranes of all tissues in the form of lipoproteins (complexes with proteins) and glycolipids (lipids containing carbohydrates). Lipoproteins are contained in cell organelles (mitochondria, etc.) and, therefore, are involved in redox processes, protein biosynthesis, and transport of substances into cells. Some hormones (genital, adrenal cortex), as well as vitamins of group D, are formed from lipids. Protective. Lipids of the skin and internal organs play a protective role. They protect the human and animal body from hypothermia (they prevent the loss of heat) and from mechanical damage to organs (for example, kidneys). Lipids secreted by the sebaceous glands give the skin elasticity and protect it from drying out. 123