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biomolecule an organic compound normally present as an essential component of living organisms plasma membrane the exterior membrane surrounding the cytoplasm of a cell cytoplasm the portion of a cell's contents outside the nucleus but within the plams membrane; includes organelles such as mitochondria cytosol the continuous aqueous phase of the cytoplasm, with its disolved solutes; excludes the organelles such as mitochondria metabolite a chemical intermediate in the enzyme-catalyzed reactions of metabolism coenzyme an organic cofactor required for the action of certain enzymes; often contains a vitamin as a component ribosome a supramolecular comple of rRNAs and proteins, approximately 18 to 22 nm in diameter; the site of protein synthesis nucleus in eukaryotes, a membrane-bounded organelle that contains chromosomes nucleoid in bacteria, the nuclear zone that contains the chromosome but has no surrounding membrane genome all the genetic information encoded in a cell or virus eukaryote a unicellular or multicellular organism with cells having a membrane-bounded nucleus, multiple chromosomes, and internal organelles prokaryote a bacterium; a unicellular organism with a single chromosome, no nuclear envelope, and no membrane-bounded organelles archaebacteria one of the five kingdoms of living organisms; includes many species that thrive in extreme environments of hight ionic strength, high temperature, and low pH eubacteria one of the five kingdoms of living organisms; they have a plasma membrane but no internal organelles or nucleus lithotroph obtain energy from inorganic molecules organotrophs obtain energy from organic molecules plasmids an extrachromosomal, independently replicating, small circular DNA molecule; commonly employed in generic engineering cytoskeleton the filamentous network providing structure and organiation to the cytoplasm; includes actin filaments, microtubules, and intermediate filaments exycytosis the fusion of an intercellular vesicle with the plasma membrane, releasing the vesicle contents to the extracellular space endocytosis the uptake of extracellular material by its inclusion within a vesicle (endosome) formed by an invagination of the plasma membrane protein macromolecule composed of one or more polypeptide chains, each with a characteristic sequence of amino acids linked by peptide bonds nucleic acid biologically occuring polynucleotides in which the nucleotide residues are linkjed in a specific sequence by phosphodiester bonds; DNA and RNA polysaccharide a linear or pranched polymer of monosaccharide units linked by glyscosidic bonds lipid a small, water-insoluble biomolecule generally containing fatty acids, sterols, or isoprenopid compounds chiral center an atom with substituents arranged so that the molecule is not superimposable on its mirror image enantiomer stereoisomers that are nonsuperimposable mirror images of each other racemic mixture an equimolar mixture of the D and L stereoisomers of an optically active compound conformation the spatial arrangement of substituent groups that are free to assume different positions in space due to the freedom of bond rotation hydrophilic "water loving" polar or charged molecules that associate (dissolve) easily in water hydrophobic "water fearing" nonpolar molecules that are insoluble in water amphipathic containing both polar and nonpolar domains micelle an aggregate of amphipathic molecules in water, with the nonpolar portions in the interior and the polar portions at the exterior surface, exposed to water hydrophobic interaction association of nonpolar groups in water to seek their most stable (disordered) state colligative property properties of solutions that depend on the number of solute particles per unit volume; ie freezing point depression equilibrium constant Keq; a constant, characteristic for each chemical reaction; relates the specific concentrations of all reactants and products at equilibrium at a given temperature and pressure pH -log[H+] pKa -log[Ka] titration curve the plot of pH versus the equivalents of base added during a titration buffer a system capable of resisting changes in pH, consisting of a conjugagte acid-base pair in which the ratio of proton acceptor to donor is near unity henderson-hasselbalch equation an equation relating the pH, the pKa, and the ratio of the concentrations of the proton acceptor (A-) and the proton donor (HA) species in a solution hydrolysis cleavage of a bond, sucha as an anhydride or peptide bond, by the addition of the elements of water, yielding two or more products hydrolases enzymes (proteases, lipases, phosphates, nucleases, for example) that catalyze hydrolysis reactions conjugate acid-base pair a proton donor and its corresponding deprotonated species; for example, acetic acid (donor) and acetate (acceptor)