Telomeres (end caps)…

are the ends of the chromosomes and are made up of nucleic acids just like the rest of the chromosome. Their purpose is to protect the rest of the chromosome from damage during the duplication process. It seems that the end of the chromosome is the most vulnerable to damage, more so than the body of the chromosome. Interestingly, bacteria, which have a circular DNA are not prone to such injury and consequently are immortal. They continue to divide and are only interrupted by hostile environments. Human beings on the other hand have strands of DNA and the telomere is the protector of the body of the chromosome. In essence, the end cap takes any possible insult. Telomeres have been compared with aglets–the plastic tips on shoelaces–because they prevent chromosome ends from fraying and sticking to each other, which would scramble an organism’s genetic information. Scrambled information can lead to disease and death.

Human beings, at birth, have long, abundant telomeres but with time, each cell division, and normal growth, there is a gradual depletion of telomeres. Telomeres essentially become shorter with each cell division. The good news is there is a mechanism to retard this process to some degree. An enzyme named telomerase adds length back to the end caps. In young cells, in young individuals, telomerase keeps telomeres from wearing down too much. The bad news is when cells divide repeatedly, there is not enough telomerase and eventually the telomeres get shorter and the cells age. In human blood cells, the length of telomeres ranges from 8,000 base pairs at birth to 3,000 base pairs as people age and as low as 1,500 in elderly people. Each time a cell divides, an average person loses 30 to 200 base pairs from the ends of that cell’s telomeres. Cells normally can divide only about 50 to 70 times, with telomeres getting progressively shorter until the cells become senescent, die, or sustain genetic damage. Interestingly, telomeres do not shorten with age in tissues such as heart muscle, where cells do not continually divide. On the other hand, telomerase remains active in sperm and eggs, which are passed from one generation to the next. If reproductive cells did not have telomerase to maintain the length of their telomeres, any organism with such cells soon would go extinct.