Biology of Aging
Cellular functions are basic life processes throughout the life span of any organism. In most tissues in the body, cells must reproduce themselves (replicate) on a regular basis in order for the tissue, and thus the organism, to survive. The study of cell replication, and the changes that occur with aging (cell senescence), is an important branch of biogerontology.
The seminal observations of Leonard Hayflick on the senescence of cells in culture are at the core of this research. Hayflick showed that cells in culture appear to senesce (grow old) and cease dividing after about fifty population doublings. When one cell splits into two, that is one population doubling. When those two cells become four that is the next doubling, and so on. This observation, made in 1965, puzzled gerontologists for decades as no mechanism could be found to explain how cells in culture could count the number of times they divided. Research on telomeres and the phenomenon of telomere shortening has provided at least one workable mechanism. Telomeres are chains of DNA at the ends of each chromosome that get shorter at each cell division in most tissues. The role of telomeres and the enzyme telomerase (telomerase controls telomere shortening) in aging and in cancer is a very promising and exciting area of research.