Tiêu đề 2-Biological molecules.pdf ✅

2 Unit 2 Biological Molecules Learning Outcomes • Define and classify biological molecules. • Discuss the importance of biological molecules • Describe biologically important properties of water (polarity, hydrolysis, specific heat, water as solvent and reagent, density, cohesion/ionization) • Discuss carbohydrates: monosaccharides (glucose), oligosaccharides (cane sugar, sucrose, lactose), polysaccharides (starches, cellulose, glycogen) • Describe proteins: amino acids, structure of proteins • Describe lipids: phospholipids, triglycerides, alcohol and esters (acylglycerol) • Give an account of RNA • Discuss conjugated molecules(glycol lipids, glycol proteins)
1 Biochemistry • Biochemistry is a branch of biology which deals with the study of chemical components and the chemical processes in living organisms. • All living organisms are made of organic and inorganic compounds. • Inorganic substances in living organisms are water, carbon dioxide, acids, bases, and salts etc. Some Basics Of Biochemistry • Living organisms contain macromolecules formed from a small number of simple molecules. • These simple molecules suggest that all life had a common origin. • The characteristics of an organism are determined by the information contained in its DN. • The DNA contains information that the cell can use to make proteins. Many proteins are enzymes, which control the physical and chemical activities of an organism. • The chemical activities that go on inside an organism can organism can be given the general term metabolism. • Metabolic reactions can be divided into two general categories: anabolic and catabolic. Anabolic reactions build up large molecules from smaller ones. While: catabolic reactions do the reverse, breaking down larger molecules. • Anabolic reactions usually involve condensation reactions ill which building-block molecules are joined together and a water molecule is released. • Catabolic reactions, such as those that occur during digestion, usually involve hydrolysis reactions in which larger molecules are split as they react with water. • In photosynthesis, plants use the energy from sunlight to build up organic molecules such as sugars from simple ones such as carbon dioxide and water. • All organisms need a supply of energy, which they obtain via respiration. In respiration organic molecules are oxidized into simpler molecules, usually carbon dioxide and water. The resulting energy is used to fuel many energy-requiring processes within the organism. CHEMICAL COMPOSITION % Total Cell Weight Bacterial Cell (prokaryote) Mammalian Cell (Eukaryote) (i) Water 70 70 (ii) Proteins 15 18 (iii) Carbohydrate 3 4 (iv) Lipids 2 3 (v) DNA 1 0.25 (vi) RNA 6 1.1 (vii) Other organic molecules (enzymes, hormones, metabolism) 2 2 (viii) Inorganic ions (Na+, K+ , Ca++, Mg++, CI – , SO etc.) 1 1
2 Water Importance § Water is the medium of life. § It is the most abundant compound in all organisms. It varies from 65 to 89 percent in different organisms. § Human tissues contain about 20 per cent water in bone cells and 85 per cent in brain cells. § Almost all reactions of a cell occur in the presence of water. It also takes part in many biochemical reactions such as hydrolysis of macromolecules. § It is also used as a raw material in photosynthesis. • Ionic substances when dissolved in water, dissociate into positive and negative ions. • Non-ionic substances having charged groups in their molecules are dispersed in water. • When in solution, ions and molecules move randomly and are in a more favorable state to react with other molecules and ions. It is because of this property of water that almost all reactions in cells occur in aqueous media. In cells all chemical reactions are catalyze by enzymes which work in aqueous environment. • Non-polar organic molecules, such as fats, are insoluble in water and help to maintain membranes, which make compartments in the cell. • Water has great ability of absorbing heat with minimum of change in its own temperature. • The specific heat capacity of water – the number of calories required to raise the temperature of 1g of water from 15 to 16°C is 1.0. This is because much of the energy is used to break hydrogen bonds. Water thus works as temperature stabilizer for organisms in the environment. Protects living material against sudden thermal changes. • Water absorbs much heat as it changes from liquid to gas. “Heat of vaporization is expressed as calories absorbed per gram vaporized.” The specific heat of vaporization of water is 574 Kcal/kg, which plays an important role in the regulation of heat produced by oxidation. • It also provides cooling effect to plants when water is transpired. • To animals when water is perspired. Evaporation of only two ml out of one liter of water, lowers the temperature of the remaining 998 ml by 1°C. H2O H+ + OH- • The water molecules ionize to form H+ and OH- ions: • This reaction is reversible but an equilibrium is maintained. At 25°C the concentration of each of H+ and OH- ions in pure water is about 10-7 mole/litre. • The H+ and OH- ions affect, and take part in many of the reactions that occur in cells • Water is effective lubricant that provides protection against damage resulting from friction. • Tears protect the surface of eye from the rubbing of eyelids. • Water also forms a fluid cushion around organs that helps to protect them from trauma.