Telomere

A repetitive DNA–protein structure at a chromosome’s end that protects it from degradation and mistaken repair. Its length changes through replication and repair, and specialized enzymes maintain it in some cells.

Shelterin: A protein complex that binds vertebrate telomeres and controls their protection, replication, and length regulation. Its proteins conceal chromosome ends from DNA-damage responses and organize the protective telomere structure.
Telomeric DNA: The tandemly repeated DNA sequence found at the ends of eukaryotic chromosomes. Its repeat-rich sequence provides the substrate for telomere-binding proteins and telomerase.
Cellular senescence: A durable state in which a cell stops dividing while remaining metabolically active. Critically short telomeres can trigger senescence by activating DNA-damage signaling.
Hermann J. Muller: An American geneticist who studied mutations and chromosome structure, receiving the 1946 Nobel Prize in Physiology or Medicine. His 1938 work on chromosome ends helped establish the concept of telomeres.
Circular chromosome: A chromosome whose DNA forms a closed loop with no free ends. Circular chromosomes avoid the exposed ends and end-replication problem that telomeres address.
Telomerase: A ribonucleoprotein enzyme that extends telomeric DNA using an internal RNA template. It counteracts sequence loss during DNA replication in cells that express the enzyme.
G-quadruplex: A four-stranded nucleic-acid structure stabilized by stacked guanine tetrads. G-rich telomeric sequences can fold into this structure and affect access by telomerase.
Cancer: A group of diseases in which abnormal cells grow and spread through uncontrolled proliferation. Many cancers reactivate telomerase to maintain telomeres and sustain cell division.
Barbara McClintock: An American geneticist who discovered transposable elements and studied chromosome behavior in maize. Her work showed that broken chromosome ends can fuse, unlike intact natural ends.
Telomere shortening: The progressive loss of telomeric DNA that can occur during cell division and in response to damage. It is a change in telomeres, not a synonym for the protective structure itself.

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