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Across 5. a chemical bond that involves the sharing of electrons to form electron pairs between atoms 6. composed of variable proportions of molecules and atoms 8. a weak bond between two molecules resulting from an electrostatic attraction between a proton in one molecule and an electronegative atom in the other. 9. large biomolecules and macromolecules that comprise one or more long chains of amino acid residues 10. the minimum quantity of energy which the reacting species must possess in order to undergo a specified reaction. 13. a complex organic substance present in living cells, especially DNA or RNA, whose molecules consist of many nucleotides linked in a long chain. 15. a diverse category of products and are generally large, complex molecules 17. a substance that can accept hydrogen ions in water and can neutralize an acid 21. usually formed when the one end of the molecule is said to possess more positive charges and whereas the opposite end of the molecule has negative charges, creating an electrical pole 22. a substance made from two or more different elements that have been chemically joined 25. the surface on which an organism (eg: plant, fungus, or animal) lives or the substance on which an enzyme can act 28. the basic unit of a chemical element. 29. a compound consisting of a nucleoside linked to a phosphate group. Nucleotides form the basic structural unit of nucleic acids such as DNA. 31. the central and most important part of an object, movement, or group, forming the basis for its activity and growth 33. each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element. 34. a substance that has a molecular structure consisting chiefly or entirely of a large number of similar units bonded together, e.g., many synthetic organic materials used as plastics and resins. 35. quantitative measure of the acidity or basicity of aqueous or other liquid solutions 36. a substance produced by a living organism which acts as a catalyst to bring about a specific biochemical reaction. 37. a substance that can dissolve other molecules and compounds

Down 1. a subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen. 2. an atom or molecule with a net electric charge due to the loss or gain of one or more electrons. 3. weak, short-range electrostatic attractive forces between uncharged molecules, arising from the interaction of permanent or transient electric dipole moments. 4. a chemical substance that neutralizes alkalis, dissolves some metals, and turns litmus red; typically, a corrosive or sour-tasting liquid of this kind. 5. a process that involves rearrangement of the molecular or ionic structure of a substance, as opposed to a change in physical form or a nuclear reaction. 7. each of more than one hundred substances that cannot be chemically interconverted or broken down into simpler substances and are primary constituents of matter 11. a simple organic compound containing both a carboxyl (—COOH) and an amino 12. a stable subatomic particle with a charge of negative electricity, found in all atoms and acting as the primary carrier of electricity in solids. 14. any of a large group of organic compounds that includes sugars, starch, and cellulose, containing hydrogen and oxygen in the same ratio as water (2:1) and used as structural materials and for energy storage within living tissues. 16. a stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron, but of opposite sign. 18. a type of chemical bonding that involves the electrostatic attraction between oppositely charged ions, or between two atoms with sharply different electronegativities, 19. a molecule containing a very large number of atoms, such as a protein, nucleic acid, or synthetic polymer. 20. a region especially of a biologically active protein (as an enzyme) where catalytic activity takes place and whose shape permits the binding only of a specific reactant molecule. 23. a group of atoms bonded together, representing the smallest fundamental unit of a chemical compound that can take part in a chemical reaction. 24. a substance that takes part in and undergoes change during a reaction. 26. A homogenous mixture of one or more solutes dissolved in a solvent. 27. a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. 30. organic substances that maintain a constant pH over a given range by neutralizing the effects of hydrogen ions. 32. any of a class of organic compounds that are fatty acids or their derivatives and are insoluble in water but soluble in organic solvents. They include many natural oils, waxes, and steroids.