system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do cells retain their information when they replace themselves?

I read that all the atoms in our bodies replace themselves every 7 years. How do we look and function the same, when the cells get replaced? How do they keep their information?
gpt
When people say DNA is the blueprint of the cell, it can almost be taken literally: it contains *all* the information the cell needs to construct a perfect replica of itself and to maintain all of its functions. Cells don't get replaced in the literal sense of the word, rather they divide. With access to sufficient amounts of nutrients that serve as building blocks, they copy everything inside them (except the mitochondria, but that is a long story not directly relevant to this question). The DNA instructs the cell to copy everything and in what order to do so, how much to make of each organelle and protein etc. In the end you are left with a body built of new atoms, but that functions and looks the same as before.

Think of it like this: If you change the bricks in a building as they break or need replacement, you will after a while have replaced the whole building. The building however looks and functions the same, because you replaced all the bricks with ones that are identical. It's the same way with your body: cells divide and "replace" themselves, but it wouldn't make sense to call them completely new as they are identical to their mother cells. If one carbon atom in your body is replaced with another carbon atom, you still have a carbon atom. Atoms don't have an identity; one atom is no different than another atom of the same kind.