GWEN SHOCKEY / SCIENCE PHOTO LIBRARY GWEN SHOCKEY / SCIENCE PHOTO LIBRARY
Illustrated diagram showing detailed chromosome structure, and depicting effects of telomerase in both aging cells and in cancer cells. Chromosome structure (top right). Chromatid, one of two strands of DNA that makes up a chromosome. Centromere connects the two chromatids and is the location where fibres attach during cell division. Telomeres, protective molecular caps of repeating DNA located at the ends of chromosomes. Telomerase and aging (bottom left). Telomerase is an enzyme that maintains telomeres and prevents shortening by adding DNA with each division of a cell. Dividing cell without telomerase where telomeres get shorter every time a cell divides. This causes eventual death of the cell which may play a role in aging. Below that is a dividing cell with telomerase. Telomerase and cancer cells at bottom right. Telomerase is overactive in tumours, it repairs telomeres allowing cancer cells to replicate indefinitely.
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