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A telomere (/ ˈ t ɛ l ə m ɪər, ˈ t iː l ə-/; from Ancient Greek τέλος (télos) 'end' and μέρος (méros) 'part') is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes (see Sequences). Telomeres are a widespread genetic feature most commonly found in eukaryotes.
Olovnikov proposed that every time a cell divides, a part of the DNA sequence is lost, and if this loss reaches a certain level, cell division will stop at the end. [ 7 ] [ 9 ] [ 16 ] According to his "marginotomy" theory, there are sequences at the end of the DNA (telomeres) that are placed in tandem repeats and create a buffer zone that ...
When telomeres reach a critically short length, sufficient shelterin proteins to inhibit checkpoint activation are not available, although NHEJ and HR generally remain inhibited at this point. [5] This loss of inhibition is one reason why telomere shortening causes senescence (Figure 1B).
Telomerase, also called terminal transferase, [1] is a ribonucleoprotein that adds a species-dependent telomere repeat sequence to the 3' end of telomeres. A telomere is a region of repetitive sequences at each end of the chromosomes of most eukaryotes. Telomeres protect the end of the chromosome from DNA damage or from fusion with neighbouring ...
Loss of telomeric DNA through repeated cycles of cell division is associated with senescence or somatic cell aging. In contrast, germ line and cancer cells possess an enzyme, telomerase, which prevents telomere degradation and maintains telomere integrity, causing these types of cells to be very long-lived.
As the cell divides, the telomeres on the end of a linear chromosome get shorter. The telomeres will eventually no longer be present on the chromosome. This end stage is the concept that links the deterioration of telomeres to aging. Top: Primary mouse embryonic fibroblast cells (MEFs) before senescence. Spindle-shaped.
Telomerase is a ribonucleoprotein polymerase that maintains telomere ends by addition of the telomere repeat TTAGGG. The enzyme consists of a protein component with reverse transcriptase activity, encoded by this gene, and an RNA component that serves as a template for the telomere repeat.
Alternative Lengthening of Telomeres (also known as "ALT") is a telomerase-independent mechanism by which cancer cells avoid the degradation of telomeres.. At each end of the chromosomes of most eukaryotic cells, there is a telomere: a region of repetitive nucleotide sequences which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes.