Biology 1 "BIO131" Lecture Notes PDF

Biology 1 “BIO131” Dr. Ahmed Deghidy PhD Molecular Biology Alex U, Alexandria, Egypt  2.4 Water: A Vital Compound Each water molecule is composed of one oxygen atom and two hydrogen atoms. The oxygen atom shares one electron with each hydrogen atom. The greater electronega...

Biology 1 “BIO131” Dr. Ahmed Deghidy PhD Molecular Biology Alex U, Alexandria, Egypt  2.4 Water: A Vital Compound Each water molecule is composed of one oxygen atom and two hydrogen atoms. The oxygen atom shares one electron with each hydrogen atom. The greater electronegativity of the oxygen atom makes the water molecule polar: “Water carries two partial negative charges (δ−) near the oxygen atom and two partial positive” Water has a simple molecular structure  Water molecules are cohesive Cohesion is the tendency of water molecules to adhere to one another due to hydrogen bonding. The cohesion of water is responsible for its surface tension. Because the surface tension of the water is greater than the force of one foot, the insect glides atop the surface of the water rather than sinking. The high surface tension of water is due to hydrogen bonding between water molecules.  Water molecules are adhesive The polarity of water causes it to be attracted to other polar molecules, this attraction is called adhesion. Water adheres to any substance with which it can form hydrogen bonds. If a glass tube with a narrow diameter is lowered into a beaker of water, the water will rise in the tube above the level of the water in the beaker, because the adhesion of water to the glass surface, drawing it upward, is stronger than the force of gravity, pulling it downward. The narrower the tube, the greater the electrostatic forces between the water and the glass, and the higher the water rises 2.5 Properties of Water The Chemical Building Blocks of Life Chapter Contents 3.1 Carbon: The Framework of Biological Molecules 3.2 Carbohydrates: Energy Storage and Structural Molecules 3.3 Nucleic Acids: Information Molecules 3.4 Proteins: Molecules with Diverse Structures and Functions 3.5 Lipids: Hydrophobic Molecules  3.1 Carbon: The Framework of Biological Molecules The framework of biological molecules consists predominantly of carbon atoms bonded to other carbon atoms or to atoms of oxygen, nitrogen, sulfur, phosphorus, or hydrogen. Reasons: 1- Because carbon atoms can form up to four covalent bonds. 2- Molecules containing carbon can form straight chains, branches, or even rings, and coils. Molecules consisting only of carbon and hydrogen are called hydrocarbons. Because carbon–hydrogen covalent bonds store considerable energy, hydrocarbons make good fuels. Ex: Gasoline.  Functional groups account for differences in molecular properties 1- Carbon and hydrogen atoms both have very similar electronegativities. 2- Electrons in C—C and C—H bonds are therefore evenly distributed, with no significant differences in charge over the molecular surface. For this reason, hydrocarbons are nonpolar. Most biological molecules produced by cells, contain other atoms which have different electronegativities “exhibit regions of partial positive or negative charge”. For this reason, hydrocarbons become polar. These molecules called functional groups. Functional groups give specific chemical properties to the molecules that possess them. Ex1: Amino groups, make a molecule more basic. Ex2: carboxyl groups make a molecule more acidic Functional groups account for differences in molecular properties  Biological macromolecules include carbohydrates, lipids nucleic acids, and proteins.  Biological macromolecules include carbohydrates, nucleic acids, proteins, and lipids A polymer is a long molecule built by linking together a large number of small, similar chemical subunits called monomers. These long chains are built via chemical reactions termed dehydration reactions and are broken down by hydrolysis reactions. Lipids are macromolecules, but they really don’t follow the monomer–polymer relationship “Lipids are formed through dehydration reactions, which link the fatty acids to glycerol”.  3.2 Carbohydrates: Energy Storage and Structural Molecules Carbohydrates contain carbon, hydrogen, and oxygen in the molar ratio 1:2:1. Their empirical formula is (CH2O)n , where n is the number of carbon atoms. Because they contain many carbon–hydrogen (C—H) bonds, which release energy when oxidation occurs, carbohydrates are well suited for energy storage. The simplest of the carbohydrates are the monosaccharides.  Sugar isomers have structural differences Glucose, fructose, and galactose are isomers with the empirical formula C6H12O6. A structural isomer of glucose, such as fructose, has identical chemical groups bonded to different carbon atoms. A stereoisomer of glucose, such as galactose, has identical chemical groups bonded to the same carbon atoms but in different orientations (the —OH at carbon 4). Your taste buds can discern them: Fructose tastes much sweeter than glucose, despite the fact that both sugars have identical chemical composition.  Disaccharides serve as transport molecules in plants and provide nutrition in animals Most organisms transport sugars within their bodies. In humans, the glucose that circulates in the blood as a simple monosaccharide. In plants and many other organisms, glucose is converted into a transport form before it is moved from place to place within the organism “to be less readily metabolized during transport”. Transport forms of sugars are commonly made by linking two monosaccharides together to form a disaccharide. Disaccharides serve as effective reservoirs of glucose because the enzymes that normally use glucose in the organism cannot break the bond linking the two monosaccharide subunits.  Disaccharides serve as transport molecules in plants and provide nutrition in animals glucose + fructose sucrose “table sugar” glucose + galactose lactose “milk sugar” Many mammals supply energy to their young in the form of lactose. Adults often have greatly reduced levels of lactase, the enzyme required to cleave lactose into its two monosaccharide components, and thus they cannot metabolize lactose efficiently. This can result in lactose intolerance in humans. Most of the energy that is channeled into lactose production is therefore reserved for offspring. For this reason, lactose as an energy source is primarily for offspring in mammals.  Polysaccharides provide energy storage and structural components Polysaccharides are longer polymers made up of monosaccharides that have been joined through dehydration reactions. 1- Starch: a storage polysaccharide, consists entirely of unbranched chains of α- glucose molecules. Each linkage occurs between the carbon 1 (C-1) of one glucose molecule and the C-4 of another, making them α-(1, 4) linkages.  Polysaccharides provide energy storage and structural components 2- Cellulose: a structural polysaccharide, consists of unbranched chain of β- glucose molecules. Each linkage occurs between the carbon 1 (C-1) of one glucose molecule and the C-4 of another, making them β-(1, 4) linkages. Cellulose fibers can be very strong and are quite resistant to metabolic breakdown, which is one reason wood is such a good building material.  Polysaccharides provide energy storage and structural components Because cellulose cannot be broken down readily by most animals, it works well as a biological structural material. But some animals, such as cows, are able to utilize cellulose aided by symbiotic bacteria and protists in their digestive tracts. These organisms provide the necessary enzymes for cleaving the β-(1 4) linkages, thus providing access to a rich source of energy. The comparable molecule to starch in animals is glycogen. 3- Glycogen is an insoluble polysaccharide containing branched α- glucose chains. Glycogen has a much longer chain length and more branches than plant starch.