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Telomeres
Telomeres "Caps" (made of repeated DNA sequences) found at the ends of chromosomes that protect the ends of the chromosomes from degradation. The telomeres on a chromosome shorten with each round of cell replication. Telomere shortening has been suggested to be a "clock" that regulates how many times an individual cell can divide (that is, when the telomeres of the chromosomes in a cell shorten past a particular point, the cell can no longer divide).
RELATED TERMS--------------------------------------
Chromosomes
Filaments of genetic material in every cell nucleus that are made up of genes and that transmit genetic information from one generation of cells to the next.
Telomeres
"Caps" (made of repeated DNA sequences) found at the ends of chromosomes that protect the ends of the chromosomes from degradation. The telomeres on a chromosome shorten with each round of cell replication. Telomere shortening has been suggested to be a "clock" that regulates how many times an individual cell can divide (that is, when the telomeres of the chromosomes in a cell shorten past a particular point, the cell can no longer divide).
Chromosome
A structural unit within a eukaryotic nucleus that carries genes. A chromosome consists of a long, continuous strand of DNA and associated proteins.
Cell
Fundamental structural unit of all life. The cell consists primarily of an outer plasma membrane, which separates it from the environment; the genetic material (DNA), which encodes heritable information for the maintainance of life; and the cytoplasm, a heterogeneous assemblage of ions, molecules, and fluid.
SIMILAR TERMS--------------------------------------
Telogen effluvium
Thinning hair. Rarely results in actual baldness.
Telomer
A small segment at the end of nuclear DNA that becomes shorter with every replication of the DNA. DNA will no longer replicate beyond a certain point of telomere reduction.
Telomerase
An enzyme composed of a catalytic protein component and an RNA template and that synthesizes the telomeric DNA at the ends of chromosomes. When active, telomerase can continually add to the length of the telomeres on the ends of chromosomes within a cell, thus conferring on that cell the ability to continue dividing past its normal lifespan.
Telophase
The final stage of mitosis in which the chromosomes migrate to opposite poles, a new nuclear envelope forms, and the chromosomes uncoil. The last phase of nuclear division in eukaryotes when the segregated chromosomes uncoil and begin to reform nuclei. This is immediately followed (in most cases) by cytokinesis.
PREVIOUS AND NEXT TERMS--------------------------------------
Tropical sprue
A condition of unknown cause. Abnormalities in the lining of the small intestine prevent the body from absorbing food normally.
Tubal ligation
Surgical sterilization procedure in which the fallopian tubes are sealed or cut to prevent sperm from reaching an egg.
Tube feeding
A way to provide food through a tube placed in the nose, the stomach, or the small intestine. A tube in the nose is called a nasogastric or nasoenteral tube. A tube that goes through the skin into the stomach is called a gastrostomy or percutaneous endoscopic gastrostomy (PEG). A tube into the small intestine is called a jejunostomy or percutaneous endoscopic jejunostomy (PEJ) tube. Also called enteral nutrition.
Tyrosine
The amino acid from which dopamine is made.
Telomerase
An enzyme composed of a catalytic protein component and an RNA template and that synthesizes the telomeric DNA at the ends of chromosomes. When active, telomerase can continually add to the length of the telomeres on the ends of chromosomes within a cell, thus conferring on that cell the ability to continue dividing past its normal lifespan.
Telomeres
Tissue culture
See culture.
Totipotent cells
Stem cells that have unlimited developmental capability. The totipotent cells of the very early embryo (an embryo prior to the blastocyst stage) have the capacity to differentiate into extraembryonic tissues, membranes, the embryo, and all postembryonic tissues and organs.
Transcription
Making an RNA copy from a gene or other DNA sequence. Transcription is the first step in gene expression.
Transformation
A genetic process resulting in a heritable alteration of the properties of a cell. In the case of cultured cells, transformation often refers to the acquisition of new properties, such as unlimited culture lifespan.
Translation
The process of forming a protein molecule from information contained in messenger RNA.
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