Atoms, Ions, and Molecules (p. 56)
1. The simplest form of matter with unique chemical properties is the element. Twenty-four elements play normal physiological roles in humans. Those called trace elements are needed in only tiny amounts.
2. An atom consists of a central positively charged nucleus of protons and usually neutrons, orbited by a usually multilayered cloud of negatively charged electrons.
3. The outermost electrons, called valence electrons, determine the chemical behavior of an element.
4. Isotopes are variations of an element that differ only in the number of neutrons. Some are unstable radioisotopes, which give off radioactivity as they change to a more stable isotope.
5. Ions are particles with one or more excess electrons or protons, and thus a negative charge (anions) or positive charge (cations). Oppositely charged ions are attracted to each other and tend to follow each other in the body.
6. Electrolytes are salts that ionize in water to form solutions that conduct electricity. These include salts of sodium, potassium, chlorine, phosphate, bicarbonate, and other elements (table 2.2).
7. Free radicals are highly reactive particles with an odd number of electrons. They have very destructive effects on cells and may contribute to aging and cancer, but the body has antioxidant chemicals that provide some protection from them.
8. A molecule consists of two or more atoms joined by chemical bonds. If the elements are nonidentical, the molecule is a compound.
9. Isomers are molecules with the same number and kinds of elements, but different arrangements of them and different chemical properties.
10. A molecule's molecular weight is the sum of the atomic weights of its elements.
11. Molecules are held together by ionic, covalent, or hydrogen bonds, or a combination of these.
Water and Mixtures (p. 63)
1. The polarity and bond angle of water result in the hydrogen bonding of water molecules to each other. Hydrogen bonding is responsible for the diverse biologically important properties of water.
2. A mixture is a combination of substances that are physically blended but not chemically combined. Most mixtures in the body are a combination of water and various solutes.
3. Mixtures can be classified as solutions, colloids, or suspensions based on the size of their particles.
4. The concentration of a mixture is expressed for differing purposes as weight per volume, percentage, molarity, or (for electrolytes) milliequivalents per liter.
5. The concentration of hydrogen ions in a solution is expressed as pH, with a range from 1 to 14. A pH of 7 is neutral (with equal quantities of H+ and OH-), a pH < 7.0 is acidic, and a pH > 7.0 is basic.
6. Buffers are chemical solutions that resist changes in pH when acid or base is added to them.
Energy and Chemical Reactions (p. 68)
1. Energy, the capacity to do work, exists in potential and kinetic forms.
2. Chemical reactions can be decomposition, synthesis, or exchange reactions.
3. Some chemical reactions are reversible; their direction depends on the relative amounts of reactants and products present. Such reactions tend to achieve an equilibrium state unless disrupted by the addition of new reactants or removal of products.
4. The rate of a chemical reaction is influenced by concentration, temperature, and catalysts.
5. Metabolism is the sum of all chemical reactions in the body. It consists of catabolism (breakdown of larger molecules into smaller ones) and anabolism (synthesis of larger molecules).
6. Oxidation is the removal of electrons from a molecule; reduction is the addition of electrons.
Organic Compounds (p. 71)
1. Organic molecules contain carbon. They often have carbon atoms arranged in a backbone with attached functional groups (carboxyl and amino groups, for example) that determine the chemical behavior of the molecule.
2. Many biologically important molecules are polymers—large molecules composed of a chain of identical or similar subunits called monomers.
3. The joining of monomers to form a polymer, called polymerization, is achieved by a dehydration synthesis reaction that removes water from the reactants. Polymers are broken up into monomers by hydrolysis reactions, which consume water to add —H and —OH to the molecules.
4. Carbohydrates are organic molecules of carbon and a 2:1 ratio of H:O. The major carbohydrates are the monosaccharides (glucose, fructose, galactose), disaccharides (sucrose, lactose, maltose), and polysaccharides (starch, cellulose, glycogen).
5. Carbohydrates are good sources of quickly mobilized energy but also play structural and other roles (table 2.6).
6. Lipids are hydrophobic compounds of carbon and a high ratio of H:O. Major classes of lipids are fatty acids, triglycerides, phospholipids, eicosanoids, and steroids.
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7. Lipids serve for energy storage, as chemical signals, and as structural components of cells, among other roles (table 2.7).
9. An amino acid is a small organic molecule with an amino (—NH2) and carboxyl (—COOH) group. Amino acids can join together through peptide bonds to form peptides from two to thousands of amino acids long. Proteins are generally regarded as peptides of 100 or more amino acids.
10. Proteins have four levels of structure: primary (amino acid sequence), secondary (an a helix or p sheet), tertiary (further bending and folding), and sometimes quaternary (attraction of two or more polypeptide chains to each other).
11. Protein function depends strongly on three-dimensional shape, or conformation. Denaturation is a destructive change in conformation, usually caused by temperature or pH changes.
12. Conjugated proteins require a nonprotein component such as a carbohydrate or an inorganic ion attached to them in order to function. The nonprotein moiety is called the prosthetic group.
13. Proteins have a wide range of structural, communication, transport, catalytic, and other functions.
14. Enzymes are proteins that function as biological catalysts. The substances they act upon are called their substrates, and bind to an enzyme at specific locations called active sites.
15. Enzymes accelerate chemical reactions by lowering their activation energy.
16. An enzyme generally reacts only with specific substrates that fit its active site.
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17. Enzymatic reactions are often linked together to form metabolic pathways.
18. Adenosine triphosphate (ATP) is a universal energy-transfer molecule composed of adenine, ribose, and three phosphate groups. It is essential to many physiological processes, and life ends in seconds in the absence of ATP.
19. Small amounts of ATP are generated by glycolysis linked, in the absence of oxygen, to anaerobic fermentation. Much larger amounts are generated when oxygen is available and glycolysis is linked to aerobic respiration.
20. The nucleic acids, DNA and RNA, are polymers of ATP-like nucleotides. They are responsible for heredity and the control of protein synthesis.
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