HUMAN MEDICAL BIOLOGY, ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedonyuk 2010

BIOLOGY

CHAPTER 1. BIOLOGICAL BASES OF HUMAN VITAL ACTIVITY

1.3. MOLECULAR-GENETIC AND CELLULAR LEVELS OF LIFE ORGANIZATION

1.3.2. Structural, chemical, and functional organization of eukaryotic cells

Organic compounds: Carbon-Containing Substances of Living Organisms

Many organic substances that make up Living organisms are characterized by large molecular sizes and are referred toering macromolecules. They largely consist of repeating structural units (monomers) and are therefore called Biopolymers. Organic substances include Proteins AND AMINO acids, Nucleic Acids and individual NUCLEOTIDES (particularly ATP), CARBOHYDRATES, Lipids, Vitamins, and Hormones.

Proteins are biopolymers whose monomers are Amino Acids covalently linked together by peptide bonds (-CO-NH-). Proteins are also called proteins. There are 20 known amino acids. Proteins are components of All living organisms; life cannot exist without them. On average, they constitute 18-20% of total body mass and about 50% of its dry mass. A compound of several amino acids is called a peptide, and A large number of amino acids form a polypeptide. A protein molecule may contain one or several Polypeptides. Proteins are high-molecular-weight substances. The Molecular Weight of Insulin is 5,700, Ribonuclease is 12,700, and Pyruvate kinase is 240,000 daltons. There are four levels of Structural Organization of protein molecules: primary, secondary, tertiary, and quaternary structures. The Primary Structure is the polypeptide chain. The Secondary structure is formed by the coiling of the polypeptide chain into a helix. This helical configuration is maintained by Hydrogen Bonds between the -COOH groups of one turn of the helix and the -NH₂ groups of another. The protein with its secondary structure then folds further in three-dimensional space, forming a tertiary structure specific to each protein. Globular and fibrous (fibrillar) proteins are distinguished. Globular proteins have a rounded shape, whereas Fibrous proteins have an elongated shape. Several polypeptide chains combine to form a quaternary structure. A typical representative of proteins with a quaternary structure is Hemoglobin. Its molecule is built from four pairwise identical structures: two a- and two b-polypeptide chains connected to a non-protein compound, the heme.

Proteins are also classified into simple and conjugated (complex) proteins. Simple proteins are those that, upon Hydrolysis, break down exclusively into amino acids. Simple proteins include Histones, protamines, albumins, globulins, etc. Complex proteins are two-component compounds composed of a simple protein and a non-protein component (the prosthetic group). If the non-protein part is a nucleic acid, such complex proteins are called Nucleoproteins; if it consists of mono- or Oligosaccharides, they are Glycoproteins; if it is lipids, they are Lipoproteins.

Functions of Proteins:

1) enzymatic (catalytic): all Enzymes are proteins or Complexes of Proteins with low-molecular-weight non-protein compounds;

2) structural: proteins are constituents of Biomembranes and the Cytoskeleton;

3) regulatory: BIOREGULATORS—hormones—are proteins;

4) receptor: with the participation of specialized Plasmalemma receptor proteins, The Cell perceives chemical signals from its microenvironment. To exert its effect on the cell, a biological substance (such as a hormone) must bind to a corresponding plasmalemma protein, with the decisive role in ensuring the selectivity (Specificity) of this interaction belonging to The structure of the carbohydrate component (oligosaccharide chains) of the receptor protein.

5) transport: human Blood serum albumins transport Fatty acids, therapeutic drugs, and toxic substances; erythrocyte hemoglobin transports oxygen;

6) contractile: Muscle contraction is driven by the proteins Actin and Myosin;

7) protective: immune defense is provided by IMMUNOGLOBULINS and lymphokines.

Nucleic acids (Section 1.2.3).

Carbohydrates are organic substances composed of carbon, oxygen, and hydrogen, where The ratio of oxygen to hydrogen is the same as in a Water molecule: two hydrogen atoms per one oxygen atom. Hence the name, carbohydrates. The general formula for carbohydrates is C_n(Н₂О)_n, where n is at least three. In animal organisms, the carbohydrate content is relatively low (1-2% of dry mass), whereas in plants it can reach up to 90% of dry mass (potato tubers). Carbohydrates are divided into Monosaccharides and Polysaccharides. Monosaccharides are called simple sugars. They consist of a single molecule, have a sweet taste, and are soluble in water. Monosaccharides containing three carbon atoms are called trioses, 4 - tetroses, 5 - pentoses, 6 - hexoses. Examples of pentoses include ribose and deoxyribose. Ribose is part of RNA, and deoxyribose is part of DNA. Hexoses include glucose, fructose, and galactose, which perform energetic functions in the Human and Animal body. Complex carbohydrates contain from two or three (oligosaccharides) to many thousands (polysaccharides) of monomeric sugar residues. Of utmost importance for humans are the Disaccharides lactose (milk sugar), sucrose, maltose, and the polysaccharide Glycogen. Functions of carbohydrates: 1) energetic; 2) structural; 3) energy reserve storage.

Lipids are organic substances characterized by insolubility in water and other polar Solvents, and The ability to dissolve in non-polar (hydrophobic) solvents (ether, gasoline, chloroform). The term "lipids" encompasses fats and fat-like substances. They are found in all Cells. Their content is small (5-15% of dry mass). However, in adipose tissue cells, fat accounts for nearly 90% of dry mass. Chemically, lipids are esters of higher carboxylic (fatty) acids and alcohols. Simple and Complex Lipids are distinguished. Simple Lipids, upon hydrolysis, break down into alcohol and fatty acids. Complex lipid molecules may include a phosphoric acid residue (Phospholipids), a carbohydrate (Glycolipids), or a protein (lipoproteins).

Vitamins are bioorganic compounds essential for the normal vital activity of organisms. They are not synthesized in The Human Body and must be obtained from food, predominantly of plant origin.

Hormones are BIOLOGICALLY ACTIVE SUBSTANCES produced by Endocrine glands and released into the BLOOD AND Lymph. They participate in the endocrine mechanisms of Homeostasis regulation (p.)