[thedoc (OP)]

Adel asked the Naked Scientists:
   what percentage of the atoms we are born with, do we die with?
What do you think?

[chris]

This is a tricky one; non-dividing cells in the body will contain DNA and proteins that last a lifetime. Such cells include neurones, cells in bone and cartilage, lens proteins in the eye, muscle. I'd need to go away and work out what fraction of the total mass these are...

[evan_au]

non-dividing cells in the body will contain DNA and proteins that last a lifetime. Such cells include neurones, cells in bone and cartilage, lens proteins in the eye, muscle.

Even among these relatively static cells, there is still change happening:
- Bone is continually formed and reformed by the action of osteoclasts and osteoblasts
- Old and degraded protein is continually marked with ubiquitin and replaced
- Dendritic spines are being reinforced and weakened
- DNA is subjected to continual mutations and repair
- Infection and other inflammatory processes result in cell death and removal