Correct Answer:
B. Protective caps at the end of chromosomes that shorten as cells divide.
In the context of Human Biology, a ‘Telomere’ is best described as “Protective caps at the end of chromosomes that shorten as cells divide.” This is the accurate definition and highlights their significance in aging. Telomeres are specialized DNA-protein structures found at the ends of eukaryotic chromosomes. Their primary function is to protect the genetic information within the chromosome during cell division.
- Every time a cell divides, a small portion of the telomere is lost because DNA replication machinery cannot fully copy the very end of the DNA strand. As telomeres progressively shorten with each cell division, they eventually reach a critical length. At this point, the cell either stops dividing (enters senescence) or undergoes programmed cell death (apoptosis). This shortening is a fundamental mechanism contributing to cellular aging and plays a crucial role in the overall aging process of an organism.
- Option A, “A brain cell that stops functioning,” is incorrect. Telomeres are parts of chromosomes in almost all somatic cells, not a specific type of brain cell, nor do they refer to cells ceasing function directly.
- Option C, “A stomach enzyme that breaks down proteins,” is incorrect. Enzymes are proteins that catalyze biochemical reactions, and telomeres are DNA-protein structures associated with chromosomes, not digestive enzymes.
- Option D, “A type of white blood cell,” is incorrect. White blood cells are part of the immune system; telomeres are sub-cellular structures found within the nuclei of cells.