Amino acid—A chemical building block of proteins. There are 20 standard amino acids. A protein consists of a specific sequence of amino acids.
Antioxidants—Compounds that neutralize oxygen radicals. Some are enzymes like superoxide dismutase (SOD) and catalase, while others are nutrients such as vitamin C.
Anti-proliferative genes—Genes that inhibit cell division or proliferation. These genes can act as tumor suppressor genes.
Base—Part of a nucleotide. In DNA, the bases are adenine (abbreviated A), thymine (T), cytosine (C), and guanine (G). RNA contains uracil (U) instead of thymine. Biomarkers—Biological changes that characterize the aging process. So far, no reliable biomarkers have been identified in humans.
Caloric restriction—An experimental intervention that is being studied to determine its impact on longevity. In laboratory settings, the lifespans of animals have been extended by reducing calories while maintaining the necessary levels of nutrients.
Centenarian—A person who has lived at least 100 years.
Chromosome—Acellular structure containing genes. Chromosomes are composed of DNA and proteins. Humans have 23 pairs of chromosomes in each body cell, one of each pair from the mother and the other from the father.
Cytokines—Proteins that are secreted by cells and regulate the behavior of other cells by binding to receptors on their surfaces. This binding triggers a variety of responses, depending on the nature of the cytokine and the target cell.
DNA—Abbreviation for deoxyribonucleic acid, the molecule that contains the genetic code for all life forms except for a few viruses. It consists of two long, twisted chains made up of nucleotides. Each nucleotide contains one base, one phosphate molecule, and the sugar molecule deoxyribose. The bases in DNA nucleotides are adenine, thymine, guanine, and cytosine.
Enyzme—A protein that promotes a specific biochemical reaction in the body without itself being permanently changed or destroyed. Enzymes, for instance, are involved in blood clotting and initiate the process of breaking down food.
Fibroblast— One of the major cell types found in skin. Scientists utilize human fibroblast cell cultures to study aging at the cellular level.
Free radicals—Molecules with unpaired electrons that react readily with other molecules. Oxygen-free radicals, produced during metabolism, damage cells and may be responsible for aging in tissues and organs.
Gene—Asegment of DNA that contains the “code” for a specific protein.
Gene expression—The process by which the information contained in the genes is transcribed and translated into proteins. Age-related changes in gene expression may account for some of the phenomena of aging.
Glycation—A process by which glucose links with proteins and causes these proteins to bind together. In some circumstances, this can result in “stiffening” of tissues and may lead to certain complications of diabetes, and perhaps some of the physiological problems associated with aging.
Hayflick limit—The finite number of divisions a cell is capable of when cultured in a laboratory setting (in vitro). A cell reaching this limit is considered to be senescent, at least when in vitro. However, to date there is no evidence that replicative senescence plays a physiologically significant role in normal aging or age-related disorders.
Interleukins—A type of cytokine involved in regulation of immune function. The levels of some interleukins present in the body are reported to change with age, but it is unclear whether these fluctuations are due to aging itself or are a manifestation of the many conditions and diseases associated with aging.
Lymphocytes—Small white blood cells that are important to the immune system. A decline in lymphocyte function with advancing age is being studied for insights into aging and disease.
Maximum lifespan—The greatest age reached by any member of a given species.
Mean lifespan—The average number of years that members of a species live; also known as life expectancy.
Mitochondria—Cell organelles that metabolize glucose and other sugars to produce biochemical energy. Mitochondria also contain DNA, which is damaged by the high level of free radicals produced during this process.
Mitosis—The process of replicating DNA, and dividing it into two equal parts to generate two identical “daughter” cells from one “mother” cell.
Nucleotide—A building block of DNA or RNA. It includes one base, one phosphate molecule, and one sugar molecule (deoxyribose in DNA, ribose in RNA).
Photoaging—The process initiated by sunlight through which the skin becomes drier and loses elasticity. Photoaging is being studied for clues to aging because it has the same effect as normal aging on certain skin cells.
Proliferative genes—Genes that promote cell division or proliferation. These genes can act as oncogenes (genes that promote cancer growth).
Proteins—Molecules composed of amino acids arranged in a specific order determined by the DNA sequence of the gene. Proteins are essential for all life processes. Certain ones, such as the enzymes that protect against free radicals and the lymphokines, produced in the immune system, are being studied extensively by gerontologists.
Replicative senescence—The stage at which a cell has permanently stopped dividing.
RNA—Abbreviation for ribonucleic acid, the molecule that carries out DNA’s instructions for making proteins. It consists of one long chain made up of nucleotides. There are three main types of RNA: messenger RNA, transfer RNA, and ribosomal RNA.
Telomeres—Repeated short DNA sequences occurring at the end of the chromosomes; telomeres shorten each time a cell divides. Tumor suppressor
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