Introduction to Basic Chemistry

1. Matter is anything that occupies space and has mass. It is made up of building units called chemical elements. Carbon, hydrogen, oxygen, and nitrogen make up 96 percent of body weight. These elements together with phosphorus and calcium make up 99 percent of total body weight. Units of matter of all chemical elements are called atoms. Atoms consist of a nucleus, which contains protons and neutrons, and orbiting electrons moving in energy levels. The total number of protons of an atom is its atomic number. This number is equal to the number of electrons in the atom.
2. The electrons are the part of an atom that actively participate in chemical reactions. A molecule is the smallest unit of two or more combined atoms. A molecule containing two or more different kinds of atoms is a compound. In an ionic bond, outer energy level electrons are transferred from one atom to another. The transfer forms ions, whose unlike charges attract each other and form ionic bonds. In a covalent bond, there is a sharing of pairs of outer-energy level electrons. Hydrogen bonding provides temporary bonding between certain atoms within large complex molecules such as proteins and nucleic acids.
3. Chemical Reactions - Synthesis reactions involve the combination of reactants to produce a new molecule. The reactions are anabolic: bonds are formed. In decomposition reactions, a substance breaks down into other substances. The reactions are catabolic: bonds are broken. Exchange reactions involve the replacement of one atom or atoms by another atom or atoms. In reversible reactions, end products can revert to the original combining molecules. The sum of all synthetic and decomposition reactions that occur within an organism is referred to as metabolism. When chemical bonds are formed, energy is needed. When bonds are broken, energy is released. This is known as chemical bond energy.
4. Inorganic substances usually lack carbon, contain ionic bonds, resist decomposition, and dissolve readily in water. Water is the most abundant substance in the body. It is an excellent solvent and suspending medium, participates in chemical reactions, absorbs and releases heat slowly, and lubricates. Acids, bases, and salts dissociate into ions in water. An acid ionizes into H+ ions, a base ionizes into OH- ions. A salt ionizes into neither H+ nor OH- ions. Cations are positively charged ions; anions are negatively charged ions. On the pH scale, 7 represents neutrality. Values below 7 indicate acid solutions, and values above 7 indicate alkaline solutions. The pH values of different parts of living organisms are maintained by buffer systems, which usually consist of a weak acid and a weak base. Buffer systems eliminate excess H+ ions and excess OH- ions in order to maintain pH homeostasis.
5. Organic substances always contain carbon and usually hydrogen. Most organic substances contain covalent bonds and many are insoluble in water. Carbohydrates are sugars or starches that provide most of the energy needed for life. They may be monosaccharides, disaccharides, or polysaccharides. Carbohydrates, and other organic molecules, are joined together to form larger molecules with the loss of water by a process called dehydration synthesis. In the reverse process called digestion or hydrolysis, large molecules are broken down into smaller ones by the addition of water. Lipids are a diverse group of compounds that includes the fats, phospholipids, steroids, vitamins E and K, and prostaglandins. Fats protect, insulate, provide energy, and are stored. Prostaglandins mimic the effects of hormones and are involved in the inflammatory response and the modulation of hormonal responses. Proteins are constructed from amino acids. They give structure to the body, regulate processes, provide protection, help muscles to contract, transport substances, and serve as enzymes. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are nucleic acids consisting of nitrogen bases, sugar, and phosphate groups. DNA is a double helix and is the primary chemical in genes. RNA differs in structure and chemical composition from DNA and is mainly concerned with protein synthesis reactions. Adenosine triphosphate (ATP) is the major energy storing molecule of living things. When its energy is liberated, it is decomposed to adenosine diphosphate (ADP). ATP is manufactured from ADP using the energy supplied by various decomposition reactions, particularly of glucose. Cyclic AMP is closely related to ATP and assumes a function in certain hormonal reactions within the cell.