5.1.4—Telomeres

Telomeres are repeated, non-coding DNA sequences at the ends of chromatids/chromosomes. They act as a buffer so that the end-copying limit of linear DNA does not immediately remove important coding DNA during repeated cell division.

• Location and composition: Telomeres occupy chromosome ends and contain repeated DNA sequences that do not code for proteins; they are DNA regions, not protein caps.
• The copying problem: The normal DNA-copying machinery cannot copy the very end of a linear DNA molecule completely, so a small terminal section may be left out during replication.
• Buffer function: Because the telomere is non-coding repeated DNA, progressive shortening can remove buffer sequence before important genes near the chromosome end are affected.
• Why shortening matters: Each repeated division can reduce the remaining buffer. Once the protective reserve is sufficiently depleted, continued accurate replication/division becomes limited rather than allowing coding DNA to be lost without consequence.
• Cautious cell-outcome link: Telomere shortening is associated with a replicative limit and can contribute to cellular senescence, but this card does not claim that it alone explains all ageing or disease.

Telomeres convert an unavoidable end-copying limitation into loss of expendable repeated sequence first. This protects coding regions near chromosome ends during repeated replication, while the gradual loss of the buffer explains why a cell’s capacity for continued division can eventually become restricted.

Telomeres are not genes and are not the same as the whole chromosome-end structure discussed in the chromosome card 4560. Do not add telomerase mechanisms, named diseases or a universal ageing claim: the supported conclusion is a protective buffer with progressive shortening and a cautious link to replicative limitation.