Basic Chemistry Interactions between atoms—chemical bonds –Chemical reaction Interaction between two or more atoms that occurs as a result of activity between electrons in their outermost energy levels –Molecule Two or more atoms joined together –Compound Consists of molecules formed by atoms of two or more elements

Basic Chemistry Chemical bonds—two types unite atoms into molecules: –Ionic, or electrovalent, bond (Figure 2-7) Formed by transfer of electrons; strong electrostatic force that binds positively and negatively charged ions together –Covalent bond (Figure 2-8) Formed by sharing of electron pairs between atoms

Basic Chemistry Hydrogen bond (Figures 2-8 and 2-9) –Much weaker than ionic or covalent bonds –Results from unequal charge distribution on molecules

Basic Chemistry Attractions between molecules –Hydrogen bonds Form when electrons are unequally shared –Example: water molecule –Polar molecules have regions with partial electrical charges resulting from unequal sharing of electrons among atoms Areas of different partial charges attract one another, forming hydrogen bonds

Basic Chemistry Chemical reactions –Involve the formation or breaking of chemical bonds –There are three basic types of chemical reactions involved in physiology: Synthesis reaction Decomposition reaction Exchange reaction

Basic Chemistry Synthesis reaction –combining of two or more substances to form a more complex substance –Formation of new chemical bonds –A + B → AB Decomposition reaction –Breaking down of a substance into two or more simpler substances –Breaking of chemical bonds –AB → A + B Exchange reaction –Decomposition of two substances and, in exchange, synthesis of two new compounds from them –AB + CD → AD + CB Reversible reactions—occur in both directions

Metabolism Metabolism—all of the chemical reactions that occur in body cells (Figure 2-10) Catabolism –Chemical reactions that break down complex compounds into simpler ones and release energy; hydrolysis is a common catabolic reaction –Ultimately, the end products of catabolism are carbon dioxide, water, and other waste products –More than half the energy released is transferred to ATP, which is then used to do cellular work (Figure 2-28)

Metabolism Anabolism –Chemical reactions that join simple molecules together to form more complex molecules –Chemical reaction responsible for anabolism is dehydration synthesis

Organic and Inorganic Compounds Inorganic compounds—few have carbon atoms and none have C–C or C–H bonds Organic molecules –Have at least one carbon atom and at least one C–C or C–H bond in each molecule –Often have functional groups attached to the carbon-containing core of the molecule (Figure 2-11)

Inorganic Compounds Water –The body’s most abundant and important compound –Properties of water (Table 2-2) Polarity –Allows water to act as an effective solvent; ionizes substances in solution (Figure 2-9) –The solvent allows transportation of essential materials throughout the body (Figure 2-12)

Inorganic Compounds Properties of water (cont.) –High specific heat Water can lose and gain large amounts of heat with little change in its own temperature Enables the body to maintain a relatively constant temperature –High heat of vaporization Water requires absorption of significant amounts of heat to change water from a liquid to a gas Allows the body to dissipate excess heat

Inorganic Compounds Oxygen and carbon dioxide –Closely related to cellular respiration –Oxygen Required to complete decomposition reactions necessary for the release of energy in the body –Carbon dioxide Produced as a waste product, also helps maintain the appropriate acid-base balance in the body

Inorganic Compounds Electrolytes –Large group of inorganic compounds, which includes acids, bases, and salts –Substances that dissociate in solution to form ions –Positively charged ions are cations –Negatively charged ions are anions

Inorganic Compounds Electrolytes (cont.) –Acids and bases Acids –Any substance that releases a hydrogen ion (H+) when in solution; “proton donor” –Level of “acidity” depends on the number of hydrogen ions a particular acid will release Bases –Electrolytes that dissociate to yield hydroxide ions (OH–) or other electrolytes that combine with hydrogen ions (H+) –Described as “proton acceptors”

Inorganic Compounds pH scale—measuring acidity and alkalinity (Figure 2-13) –pH indicates the degree of acidity or alkalinity of a solution –pH of 7 indicates neutrality (equal amounts of H+ and OH–) –pH of less than 7 indicates acidity –pH of more than 7 indicates alkalinity

Inorganic Compounds Buffers –Maintain the constancy of the pH –Minimize changes in the concentrations of H+ and OH– ions –Act as a “reservoir” for hydrogen ions

Inorganic Compounds Salts (Table 2-3) –Compounds that result from chemical interaction of an acid and a base –Reaction between an acid and a base to form a salt and water is called a neutralization reaction