If all the cell in our body are replaced at some point in our life, why do we get old and die?

Question

If all the cell in our body are replaced at some point in our life, why do we get old and die?

In: Biology

Answer 1

Cell replacement slows and eventually becomes rife with chromosomal errors, at least for many cells in the body. Telomeres are little bits that “cap” the end of chromosomes, and they protect the chromosome when it divides, reducing replication errors and mutations. These telomeres shorten with each replication, so that over time, more and more replication errors and mutations happen. Eventually, those errors interfere with further replication and cells can no longer replace themselves, and that’s that – tissues break down, you age more and more, and you die.