How do our cells know how old they are?
I heard that our cells replace themselves every 18 months which means our bodies are actually only 18 months old. How do the cells, the new cells carry the information about our real chronological age forward into the next generation of cells?
Steve - First of all, some cells in our body don't divide such as nerve cells and so they really aren't. They last our whole lives but even the cells that do turn over- a new cell is generated from the division of an existing cell. The age of an existing cell basically gets transferred. The new cell remembers how old the other cell was. One of the important things that is transferred are the chromosomes. The ends of the chromosomes - called telomeres - get shorter every time a cell divides. They are a very useful counting mechanism. These telomeres shortening is one of the important counting mechanisms that tells our cells how many times they've divided and how old they are.