CTAB See HEXADECYLTRIMETHYLAMMONIUM BRO-

mass. See also MEDIUM, AGAR, CELL CULTURE,

MAMMALIAN CELL CULTURE.

Curing Agent A substance that increases the rate of loss of plasmids during bacterial

growth. See also GROWTH (MICROBIAL), PLASMID.

Current Good Manufacturing Practices

See cGMP.

Cut An enzyme-induced, highly specific break in both strands of a DNA molecule (opposite one another). The enzymes involved are called restriction enzymes. See also RESTRICTION

ENDONUCLEASES, ENZYME, DEOXYRIBONUCLEIC

ACID (DNA).

Cyclic AMP A molecule of AMP (adenosine monophosphate) in which the phosphate group is joined to both the 3′ and the 5′ positions of the ribose, forming a cyclic (ring) structure. When cAMP binds to CAP, the complex is a positive regulator of procaryotic transcription. See also ADENOSINE

MONOPHOSPHATE (AMP), CAP, PROCARYOTES,

TRANSCRIPTION, ADENILATE CYCLASE.

Cyclic Phosphorylation Synthesis (manufacturing) of adenosine triphosphate (chemical reaction) that occurs during photosynthesis in plants. Also called PHOTOSYNTHETIC PHOSPHORYLATION (photophosphorylation). See

also ATP SYNTHASE, ADENOSINE TRIPHOSPHATE

(ATP), PHOTOSYNTHESIS, PHOTOSYNTHETIC PHOS-

PHORYLATION.

Cyclodextrin A macrocyclic (doughnutshaped) carbohydrate ring produced enzymatically from starch. The external surface is hydrophobic while the interior is hydrophilic in nature. The hole of the doughnut is large enough to accommodate guest molecules. Uses include solubilization, separation, and stabilization of molecules in the interior cavity of, or in association with, the cyclodextrin molecules.

Cycloheximide Also called actidione. A chemical that inhibits protein synthesis by the 80S eucaryotic ribosomes; it does not, however, inhibit the 70S ribosomes of procaryotes. The chemical blocks peptide bond formation by binding to the large ribosomal subunits. See also PROTEIN, RIBOSOMES.

Cyclooxygenase Abbreviated COX, it is an enzyme that converts arachidonic acid to prostaglandins in the human body. There are two forms of cyclooxygenase: COX-1,

which converts arachidonic acid to constitutive prostaglandins, which help to maintain the tissues of the stomach, kidneys, and intestines, and COX-2, which converts arachidonic acid to inducible prostaglandins, which can cause pain and inflammation in the body’s joints when they accumulate in those joints. Aspirin and some other painrelieving drugs chemically block the abovedescribed activity of COX-1 and/or COX-2.

See also ENZYME, ARACHIDONIC ACID, PLATELETS, INDUCIBLE ENZYMES, SELECTIVE APOPTOTIC

ANTI-NEOPLASTIC DRUG (SAAND), EICOSANOIDS.

Cyclosporin An immune-system-supressing drug isolated from a mold in the mid-1970s by the Swiss firm of F. Hoffmann-LaRoche & Co. AG. The drug is used to prevent an (organ recipient’s) immune system from rejecting a transplanted organ and typically must be taken by the organ recipient for the duration of his or her lifetime. Cyclosporin’s mechanism of action is to prevent the divalent calcium cation (Ca 2+) from entering T lymphocytes to activate certain genes within those T lymphocytes (that trigger the rejection process). In 1996, Thomas Eisner reported that the mold Tolypocladium inflatum, from which cyclosporin is harvested, prefers a natural (wild) substrate of a deceased dung beetle. During 2000, it was discovered that cyclosporin inhibits growth of the parasitic microorganism Toxoplasma gondii (which can cause loss of sight, and neurological disease in humans). See also

T LYMPHOCYTES , FUNGUS, XENOGENEIC ORGANS,

CATION, GENE, GRAFT-VERSUS-HOST DISEASE

(GVHD), HUMAN LEUKOCYTE ANTIGENS (HLA),

MAJOR HISTOCOMPATIBILITY COMPLEX (MHC),

MICROORGANISM, GROWTH (MICROBIAL).

Cyclosporine See CYCLOSPORIN.

Cysteine (cys) An amino acid of molecular weight (mol wt) 121 Daltons. Incorporated in many proteins, it possesses a sulfhydryl group (SH) that makes cysteine a mild reducing agent. Cysteine can cross-link with another cysteine located on the same or on a different polypeptide chain to form disulfide bridges. The “free” cysteine group is called a thiol group. High levels of cysteine content in certain genetically engineered corn (maize) kernels have been shown to

inhibit in-field production of mycotoxins in corn (e.g., by several species of fungi that can be carried into corn plants by insects).

occur in mitochondria and function as electron carriers in biological oxidation. Cytochromes are involved in the “handing off ” of electrons to each other in a stepwise fashion. In the process of “handing off,” other events

Ctake place which result in the production of energy that the cell needs and is able to use.

See also PROTEIN, ENZYME, MITOCHONDRIA, CELL.

Cytochrome P450 An enzyme within the liver that contains an iron-heme cofactor. It catalyzes many different biological hydroxylation reactions. Essentially, the enzyme renders fatsoluble (hydrophobic) molecules water soluble or more water soluble (by introduction of the hydrophilic hydroxyl group), so that the molecules may be removed (washed) from the body via the kidneys. This enzyme is being investigated for its potential as a catalyst in the hydroxylation of specific (valuable) industrial chemicals. See also CYTOCHROME,

ENZYME, COFACTOR, HEME, HYDROXYLATION

REACTION, CYTOCHROME P4503A4.

Cytochrome P4503A4 An enzyme within the liver that, in humans, catalyzes reactions involved in the metabolism (breakdown) of certain pharmaceuticals. Those pharmaceuticals include some sedatives, antihypertensives, the antihistamine terfenadine, and the immunosuppressant cyclosporin. See also

ENZYME, CYTOCHROME P450, METABOLISM, HIS-

TAMINE, CYCLOSPORIN, METABOLIC PATHWAY,

CYTOCHROME.

Cytokines A large class of glycoproteins similar to lymphokines but produced by non- l y m p h o cy t i c c e l l s s u c h a s n o r m a l macrophages, fibroblasts, keratinocytes, and a variety of transformed cell lines. They participate in regulating immunological and inflammatory processes, and can contribute to repair processes and to the regulation of normal cell growth and differentiation. Although cytokines are not produced by glands, they are hormone-like in their intercellular regulatory functions. They are active at very low concentrations and for the most part appear to function nonspecifically.

For example, the cytokines stimulate the endothelial cells to express (synthesize and present) P-selectins and E-selectins on the internal surfaces (of blood vessels). These selectins protrude into the bloodstream,

which causes passing white blood cells (leukocytes) to adhere to the selectins, then leave the bloodstream by “squeezing” between adjacent endothelial cells. Cytokines are exemplified by the interferons. See also

INTERLEUKIN-1 (IL-1), LYMPHOKINES, INTERFER-

ONS, GLYCOPROTEIN, PROTEIN, T CELLS, INTER-

L E U K I N - 6 (I L - 6), M A C R O P H A G E , L E C T I N S ,

FIBROBLASTS, HORMONE, ENDOTHELIAL CELLS,

ENDOTHELIUM, SELECTINS, P-SELECTIN, ELAM-1,

LEUKOCYTES, ADHESION MOLECULE.

Cytolysis The dissolution of cells, particularly by destruction of their surface membranes.

See also LYSIS, CECROPHINS, LYSOZYME, MAGAI-

NINS, COMPLEMENT, COMPLEMENT CASCADE.

Cytomegalovirus (CMV) A virus that infects different groups of people in varying amounts, depending on their behavior. For example, 40–90% of American heterosexuals, and about 95% of homosexuals are infected with CMV. CMV normally produces a latent (nonclinical, nonobvious) infection, but with AIDS or other events can cause immune system suppression. CMV produces a febrile (fever-causing) illness that is usually mild in nature but can become retinitis (eye infection). CMV can be treated (to halt lifeand sight-threatening infection) in immunocompromised patients (i.e., transplant patients and AIDS victims) with Ganciclovir™, an antiviral compound developed by Syntex or Foscarnet™, a compound developed by Astra Pharmaceuticals. In 1996, Stephen E. Epstein found that latent CMV may cause changes in artery wall cells that aid clogging of arteries in adults (especially following balloon angioplasty). See also VIRUS,

ACQUIRED IMMUNE DEFICIENCY SYNDROME (AIDS).

Cytopathic Damaging to cells.

Cytoplasm The protoplasmic contents of the cell not including the nucleus. See also

NUCLEUS, CELL, PROTOPLASM, CYTOPLASMIC DNA, PLASMA MEMBRANE, MITOCHONDRIA,

CHLOROPLASTS.

Cytoplasmic DNA The DNA within an organism (e.g., plant) that is not inside the cell’s nucleus. Cytoplasmic DNA (i.e., located in the cell’s mitochondria and the chloroplasts) is not transferred from plant to plant via pollen, as nuclear DNA is. See also DEOXYRIBONUCLEIC

ACID (DNA), ORGANISM, CELL, CYTOPLASM,