AMP, or Adenosine monophosphate -- One of the four nucleotides in a RNA molecule. Two phosphates are added to AMP to form ATP.

ATP, or Adenosine triphosphate -- Nucleoside triphosphate composed of adenine, ribose, and three phosphate groups that is the primary carrier of chemical energy in cells. The terminal phosphate groups are highly reactive in the sense that their hydrolysis, or transfer to another molecule, takes place with the release of a large amount of free energy.

Beri-beri -- A deficiency disease characterized by inflammatory or degenerative changes in the nerves, heart, and digestive system, caused by inadequate thiamine (vitamin B-1).

Bilirubin -- A reddish yellow pigment produced from the breakdown of the hemoglobin in red blood cells, and normally excreted in bile. In cases of liver or bile duct disease, it can accumulate in the blood and tissues and produce jaundice.

Biochemistry, or biological chemistry -- The study of the chemical substances and vital processes occurring in living organisms; "the chemistry of life," or the study of the structure and properties of molecules in living organisms and how those molecules are made, changed, and broken down.

Catalyst -- A substance, typically used in small amounts relative to the reactants, that modifies and increases the rate of a reaction without being consumed in the process.

Cell respiration -- The metabolic processes by which certain organisms obtain energy from organic molecules. These processes take place in the cells and tissues, release energy, and produce carbon dioxide that is absorbed by the blood and transported to the lungs.

Chromatography -- Any of several techniques for the separation or purification of complex mixtures that rely on the differential affinities, or the attractions or forces between particles that cause them to combine, of substances for a gas or liquid mobile medium (such as gelatin) and for a stationary adsorbing medium (such as paper) through which they pass.

Citric acid cycle -- See Krebs cycle.

Coenzyme -- An organic non-protein compound that forms the active portion of an enzyme molecule.

DNA, or deoxyribonucleic acid -- The fundamental substance of which genes are composed; an antiparallel double helix of nucleotides linked by phosphodiester, or sugar-phosphate, bonds to adjacent nucleotides in the same chain and by hydrogen bonds to complementary nucleotides in the opposite chain.

Endonuclease -- Any of a group of enzymes catalyzing the hydrolysis of bonds between nucleic acids in the interior of a DNA or RNA molecule.

Enzyme -- A protein molecule that catalyzes chemical reactions of other substances without itself being destroyed or altered by the reactions. Made up of a complex of amino-acids, enzymes are part of every chemical reaction in living things. They aid in digestion, the growth and building of cells, and all reactions involving transformation of energy. Inside the cell, enzymes create RNA and DNA by facilitating the reaction of ribose with adenosine. They also specify the sites for linking to build RNA along a DNA template. Each enzyme works only on one specific substance (called the substrate). Enzymes are usually designated by the suffix --ase.

Escherichia coli, or E. coli -- A common bacterium that has been studied intensively by geneticists because of its small genome size, normal lack of pathogenicity, and ease of culture in the laboratory.

Gene -- A hereditary unit consisting of a sequence of DNA occupying a specific location on a chromosome and determines a particular characteristic in an organism.

Genetic engineering -- The popular term for recombinant DNA technology.

Gilbert syndrome -- An inborn error of bilirubin metabolism, probably autosomal dominant, characterized by a benign elevation of indirect bilirubin in the blood, and sometimes mild jaundice, with no liver damage or hematological abnormalities.

Glucose -- The major sugar in the body and a key molecule in energy metabolism.

Hemoglobin -- The iron-rich respiratory pigment in red blood cells of vertebrates, consisting of about 6 percent heme (the prosthetic groups of cytochromes) and 94 percent polypeptide globin.

In vitro -- An experimental situation outside a living cell or organism; biological or chemical work done in the test tube, instead of in living systems. "In vitro" is Latin for "in glass."

Insulin -- A polypeptide hormone secreted by beta cells in the pancreas. Insulin helps regulate glucose metabolism by promoting a decrease in the sugar content of the blood, functioning as a complement with glucagon.

Isotopic labeling -- Adding a radioactive isotope, a form of a chemical element which has a different number of neutrons than protons, rendering the element unstable, into a compound to more easily track the compound's presence through a series of reactions.

Jaundice -- A condition characterized by high levels of bilirubin in the blood and deposits of it in the skin, mucous membranes, and sclera, resulting in a yellow appearance. Often a symptom of liver disease.

Kinase -- A class of enzymes that catalyze the transfer of phosphate groups from a high-energy phosphate-containing molecule (such as ATP) to a substrate.

Krebs cycle, or citric acid cycle -- A series of enzymatic reactions in aerobic organisms involving the oxidative metabolism of acetyl units and producing high-energy phosphate compounds (e.g., ATP) which serve as the main source of cellular energy.

Ligase -- A class of enzymes that catalyze the formation of a bond between two substrate molecules, coupled with the hydrolysis of a pyrophosphate bond in ATP or a similar energy donor. Also called synthetase.

Metabolic pathway -- A series of individual chemical reactions that combine to either break down a large compound into smaller units or that synthesize more complex molecules from smaller ones. The product of one reaction in a pathway serves as the substrate, or the substance acted upon, for the following reaction.

Metabolism -- The chemical reactions occurring in a living cell which provide energy for vital processes and activities, and assimilate new material.

Molecular biology -- The branch of biology dealing with the formation, structure, and function of macromolecules essential to life, such as DNA, RNA, and proteins, especially their role in cell replication and the transmission of genetic information.

Nucleoside -- A molecule composed of a purine or pyrimidine base covalently linked to a ribose or deoxyribose sugar.

Nucleotide -- A unit that polymerizes into nucleic acids (DNA or RNA). Each nucleotide consists of a nitrogenous base, a sugar (ribose in the case of RNA, deoxyribose in the case of DNA), and a phosphate molecule.

Oligonucleotide -- A molecule usually composed of 25 or fewer nucleotides; used as a DNA synthesis primer.

Organic molecule -- A molecule that contains carbon, such as butane (C4H10) or ethanol (C2H6O).

Oxidation -- Oxidation is the loss of one or more electrons by an atom, molecule, or ion. Oxidation is accompanied by an increase in oxidation number on the atoms, molecules, or ions that lose electrons.

Pellagra -- A deficiency disease characterized by dermatitis, inflammation of mucous membranes, diarrhea, and psychiatric disturbances, caused by inadequate niacin (one of the B complex vitamins).

Polymerase -- An enzyme that catalyzes the synthesis of nucleic acids on preexisting nucleic acid templates, such as assembling RNA from ribonucleotides or DNA from deoxyribonucleotides.

Polynucleotide -- A DNA polymer composed of multiple nucleotides.

Polyribonucleotide -- An oligonucleotide, a short polymer of two to twenty nucleotides, consisting of a number of ribonucleotides, which are the nucleotides that contain ribose as their sugar, and which are components of RNA.

Protein -- A large molecule composed of one or more chains of amino acids in a specific order. The order is determined by the base sequence of nucleotides in the gene that codes for the protein. Proteins are required for the structure, function, and regulation of the body's cells, tissues, and organs. Each protein has unique functions.

Recombinant DNA, rDNA, hybrid strings -- A unique DNA sequence formed by the joining, usually in vitro, of two non-homologous DNA molecules.

Restriction enzyme -- An endonuclease which recognizes a specific sequence of bases in a DNA molecule. Each restriction enzyme has a single, specific recognition sequence, and binds to a DNA molecule at a specific site. As a result, treatment of a particular DNA molecule with a particular restriction enzyme will always produce the same set of DNA fragments.

Ribonucleotide -- A subunit that polymerizes into the nucleic acid RNA. Each nucleotide consists of a nitrogenous base, a sugar (ribose), and one to three phosphate groups.

Ribosome -- A complex organelle composed of proteins and rRNA that catalyzes translation of messenger RNA into an amino acid sequence. Ribosomes consist of two non-identical subunits each consisting of a different rRNA and a different set of proteins.

Rickets -- A deficiency disease that affects children during the period of skeletal growth, characterized by soft and deformed bones. Rickets is caused by failure to assimilate and use calcium and phosphorus, usually due to inadequate sunlight or vitamin D.

RNA, or ribonucleic acid -- A single-stranded nucleic acid that performs an important role in the flow of genetic information. It is similar to DNA but has ribose sugar, rather than deoxyribose sugar, and uracil, rather than thymine, as one of the pyrimidine bases.

Scurvy -- A disease caused by deficiency of vitamin C. It is characterized by spongy and bleeding gums, bleeding under the skin, and extreme weakness.

Substrate -- The substance acted upon and changed by an enzyme during a biochemical reaction. Enzymes, unlike most chemicals which act as catalysts (chemicals that speed or slow the rate of a reaction without being changed during the course of a reaction), are highly specific, bonding with only a few different substrates, limiting the paths a reaction may take.

Sulfa drug -- Any of the various synthetic organic bacteria-inhibiting drugs that are closely related to sulfanilamide.

Virus -- Any one of a group of minute infectious agents that are not visible under a light microscope and are characterized by a lack of independent metabolism and an ability to replicate only within living host cells. Even though they are not living organisms, like living organisms they have the ability to pass genes through multiple generations and to mutate. The individual virus particle consists of a strand or strands of nucleic acid (which may be either DNA or RNA) and a protein shell. Viruses are classified into three main subgroups based on their host, bacterial viruses, plant viruses, and animal viruses. Viruses are then further classified by their origin, means of transmission, or illnesses they produce.

Vitamin C, or ascorbic acid -- A white, crystalline vitamin found in citrus fruits, tomatoes, potatoes, and leafy green vegetables. Vitamin C is vital to the production of collagen, the most common component of all connective tissue, and used to prevent scurvy.

Yeast -- A vague term used to refer to one of the largest groupings of fungi. Yeasts are single-celled, usually rounded fungi that reproduce by budding. Some transform into a colonial stage (mold) under certain environmental conditions, while others always remain single-celled. A few yeasts cause illness in humans.

Yellow fever -- A viral disease caused by the yellow fever virus and transmitted to humans through the bites of infected mosquitoes. The virus remains silent during an incubation period of three to six days. This is followed by two distinct disease phases. The first, or "acute," phase is normally characterized by fever, muscle pain, headache, chills, high fever, loss of appetite, nausea, and/or vomiting. After three or four days, most infected persons improve and symptoms disappear. Approximately one in five infected persons enter the second, or "toxic," phase within twenty-four hours. The patient rapidly develops a fever, jaundice (hence the term yellow fever), and abdominal pain with vomiting. Bleeding might occur from the mouth, nose, eyes and/or stomach. Blood may appear in the vomit or feces. Kidney function deteriorates and may fail entirely. Half of patients who enter the "toxic" phase die within ten to fourteen days.