Glossary

Alcohol Research & Health, Winter, 2006

Acetaldehyde: A toxic byproduct of alcohol metabolism.

Acetate: A salt or ester of acetic acid; produced from the metabolism of acetaldehyde.

Adduct: Product of the addition of one compound (e.g., acetaldehyde) to another compound (e.g., DNA).

Adenosine triphosphate (ATP): A molecule, generated largely in the mitochondria, that provides the energy needed for many key metabolic reactions.

Alcohol dehydrogenase (ADH): An enzyme that breaks down alcohol by oxidation, converting it to acetaldehyde. (See cytochrome P450.)

Aldehyde dehydrogenase (ALDH): An enzyme that converts acetaldehyde to acetate.

Allele: One of two or more variants of a certain gene.

Amine: A type of organic compound that contains nitrogen as a central atom.

Amino acids: The principal building blocks of proteins and enzymes.

Amino group: A group of atoms found in all amines and amino acids.

Antibody: A protein produced by certain immune cells that recognizes and binds to foreign proteins, leading to the destruction of those proteins.

Antibody-dependent cell-mediated cytotoxicity (ADCC): A mechanism of cell-mediated immunity whereby certain immune cells actively break up a target cell that has been bound by specific antibodies.

Antioxidant: A substance, such as glutathione, vitamin E, or an enzyme, that inhibits oxidation and that scavenges free radicals and protects the cell against damage caused by these radicals.

Apoptosis: Cell death in which the affected cell participates by activating a cascade of biochemical reactions that lead to death; also known as programmed cell death or cell suicide.

Aromatic amino acids: A class of amino acids, including phenylalanine and tryptophan, in which some of the constituent atoms form a ring.

Catalase: An enzyme that catalyzes the decomposition of hydrogen peroxide into water and oxygen.

Central vein: Blood vessel located in the center of each liver lobule through which cleansed blood exits the lobule and which feeds into the hepatic vein; also called hepatic venule.

Cytochrome P450: A family of cytochromes, one of which (CYP2E1) can oxidize alcohol to form acetaldehyde; high alcohol levels stimulate CYP2E1 activity.

Cytochromes: Specialized enzymes within mitochondria and other cell structures. Different cytochromes play important roles in metabolizing toxic substances, drugs, and other chemicals, as well as in producing adenosine triphosphate (ATP).

Cytokines: A family of molecules, produced primarily by cells of the immune system, that regulate cellular interactions and other functions. Many cytokines play important roles in initiating and regulating inflammation.

Cytoplasm: The substance filling the cell, including the cytosol as well as mitochondria, endoplasmic reticulum, and other cell structures (organelles) but excluding the nucleus.

Cytosol: The fluid portion of the cytoplasm.

Electron: A subatomic particle with a negative charge.

Endocytosis: Mechanism by which specific molecules are ingested into the cell.

Endoplasmic reticulum: A system of folded membranes that loop back and forth, spreading throughout the cytoplasm and providing a large surface area for cell reactions.

Endothelial cells: Type of cell lining the body cavities and blood vessels; control the passage of materials and the transit of white blood cells into and out of the bloodstream.

Enzyme: A substance, usually a protein, that directs and accelerates chemical reactions in the body but does not itself undergo permanent change.

Expression (i.e., gene expression): The process by which the genetic information encoded in a gene's DNA sequence is converted into a functional protein.

Fatty Acids: A major component of fats that is used by the body for energy and tissue development.

Fibrosis: The formation of scar tissue.

Free radicals: Highly reactive molecular fragments that frequently contain oxygen. (See reactive oxygen species [ROS].)

Genotype: The complete genetic makeup of an organism determined by the particular combination of alleles for all genes.

Hepatic vein: A large vessel that receives blood after it has passed through the central veins of the liver lobules.

Hepatocytes: The principal cells of the liver, which carry out most of the liver's metabolic activities.

Heterozygous: Carrying two different alleles of a given gene.

Homozygous: Carrying two copies of the same allele of a given gene.

Hyperlipidemia: Excess fat in the blood.

Hyperuricemia: Excess uric acid in the blood.

Hypoxia: Lower-than-normal levels of oxygen.

Isozymes/Isoenzymes: Enzymes that differ in amino acid sequence but catalyze the same chemical reaction.

Ketosis: Abnormal accumulation in the body of ketones, which are end products of fatty acid metabolism. Ketosis occurs when the body cannot metabolize sufficient carbohydrates to generate the energy needed (e.g., in patients with diabetes or during starvation).

[K.sub.m]: A measurement used to describe the activity of an enzyme. It describes the concentration of the enzyme's substrate at which the enzyme works at 50 percent capacity.

Kupffer cells: Specialized immune cells in the liver that filter bacteria and other foreign substances from the blood and produce antibodies and cytokines. (See also sinusoids.)