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Section 2-1 Notes Atoms Life depends on chemistry. The basic unit of matter is the atom. Atoms are incredibly small The subatomic particles that make up atoms are protons, neutrons, and electrons. Parts of an Atom Protons and neutrons have about the same mass. Protons are Positively charged (+). Neutrons carry no charge. Strong forces bind protons and neutrons together to form the nucleus. Parts of an Atom Electrons are negatively charged particles (-). Electrons have 1/1840 the mass of a proton. Electrons are in constant motion in the space surrounding the nucleus. Elements and Isotopes A chemical element is a pure substance that consists entirely on one type of atom. More than 100 elements are known, but only about two dozen are commonly found in living organisms. Isotopes Atoms of an element can have different numbers of neutrons known as isotopes. Isotopes are identified by their mass numbers. Because they have the same number of electrons, all isotopes of an element have the same chemical properties. Isotopes Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time. Radiation from certain isotopes can be used to treat cancer and to kill bacteria that cause food to spoil. Chemical Compounds In nature, most elements are found combined with other elements in compounds. The physical and chemical properties of a compound are usually very different from those of the elements from which it is formed. Chemical Bonds The atoms in compounds are held together by chemical bonds. The electrons that are available to form bonds are called valence electrons. There are two types of chemical bonds Ionic-transferred from one atom to another. Covalent-shared between atoms. When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules. (van der Waals forces) Section 2-2 Notes Water is a polar molecule The oxygen atom (with 8 protons) has a much stronger attraction to electrons than the hydrogen atom (1 proton each) Therefore, the oxygen end has a slightly negative charge and the hydrogen end has a slightly positive charge When this occurs we say the molecule is polar Hydrogen Bonds Polar molecules are attracted to each other A hydrogen bond forms from the attraction of the hydrogen atom on one H2O molecule to the oxygen atom on another Cohesion is an attraction between molecules of the same substance Ex. Water Adhesion is an attraction between molecules of different substances Ex. Water and a glass beaker Mixtures A mixture is a material composed of two or more elements or compounds that are physically mixed Two Types 1. Suspensions Mixtures of water and nondissolved materials Ex. Sand and water Mixtures 2. Solutions Substances are evenly distributed throughout the solution Solute – the substance that is dissolved Solvent – the substance in which the solute dissolves Water is the greatest solvent on Earth Blood is a good example of both a solution and a suspension The pH Scale A water molecule (H2O) can form a hydrogen ion (H+) and a hydroxide ion (OH-) Chemists often measure the concentration of H+ ions The pH scale indicates the concentration of H+ ions in a solution The pH scale ranges from 0 - 14 The pH Scale Pure Water has a pH of 7 which is neutral Acid – any compound that forms H+ ions in solution pH values below 7 Produce higher concentrations of H+ ions than pure water The pH Scale Base – any compound that produces OH- ions in solution pH values above 7 Produce lower concentrations of H+ ions than pure water Your body uses buffers to control pH Buffers are weak acids or bases that can react with strong acids or bases to prevent sudden changes in pH Section 2-3 The Chemistry of Carbon The Chemistry of Carbon Carbon atoms have 4 valence electrons. Each electron can join with an electron from another atom to form a strong covalent bond. Carbon can also bond to other carbon atoms. These carbon-carbon-bonds can be single, double, or triple bonds. Carbon has the ability to form millions of different large and complex structures. Methane Acetylene Butadiene Benzene Isooctane Macromolecules Macromolecules means “giant molecules.” Formed by a process known as polymerization. Smaller units, monomers, join together to form polymers. The monomers in a polymer may be alike or different. Organic Compounds There are 4 groups of organic compounds found in living things: 1.)carbohydrates 2.)lipids 3.)nucleic acids 4.)proteins Carbohydrates Carbohydrates are compounds made up of carbon, hydrogen, and oxygen. Living things use carbohydrates as their main source of energy. Plants and some animals also use carbohydrates for structural purposes. Starches and sugars are examples of carbohydrates. Single sugar molecules are called monosaccharides. EX: glucose-sugars, galactose-milk, fructose-fruits Many sugar molecules are called polysaccharides. Many animals store excess sugar called glycogen. (animal starch) When glucose levels in your body run low your liver releases glycogen. Your muscles use stored glycogen for movement. Lipids Large molecules that are not soluble in water. (fats, oils, & wax) Made mostly from carbon and hydrogen atoms. Can be used to store energy. Some are parts of biological membranes and waterproof coverings. Nucleic Acids Macromolecules containing hydrogen, oxygen, nitrogen, carbon, and phosphorus. Are polymers assembled from individual monomers called nucleotides. 3 parts: a 5-carbon sugar, phosphate group, and a nitrogenous base. Store and transmit hereditary, or genetic information. 2 types: 1.)ribonucleic acid (RNA) 2.)deoxyribonucleic acid (DNA) Proteins Macromolecules that contain nitrogen, carbon, hydrogen, and oxygen. Polymers of molecules called amino acids. Amino acids are compounds with an amino group (NH2) on one end and a carboxyl group (COOH) on the other. General structure Alanine Serine Proteins Some proteins control the rate of reaction and regulate cell processes. Some are used to form bones and muscles Others transport substances into or out of cells and fight diseases. Section 2-4 Notes Chemical Reactions Everything that happens in an organism is based on chemical reactions A chemical reaction is a process that changes one set of chemicals into another Elements or compounds that enter a chemical reaction are called reactants Elements or compounds that result from a chemical reaction are called products Reactants Products Energy in Reactions Chemical reactions always involve breaking the bonds in reactants and forming new bonds in products Energy is always involved in chemical reactions Either by releasing it or absorbing it Energy is released in the form of heat, but sometimes light or sound as well Every reaction needs energy to start called Activation Energy Fig. 2-19 Enzymes Some reactions we depend on to live are very slow To speed these reactions up we use special chemicals known as catalysts Catalysts work by lowering a reaction’s activation energy Enzymes are proteins that act as biological catalysts Fig. 2-20 Enzyme Action In an enzyme-catalyzed reaction, the reactants are known as substrates Substrates bind to a site on the enzyme called an active site These binding sites are very specific so we compare them to a lock and key Substrates remain bound to the enzyme until the reaction is finished When done, the products are released Enzyme Action Enzymes are affected by several factors Enzymes work best with certain values for both temperature and pH Cells have the ability to turn enzymes “on” or “off” during specific times in the cell’s life cycle
