Old cells die through apoptosis or necrosis and new cells replace them through cell division and replication. Does this process decrease in frequency over time? Why does that happen?
In: Biology
ELI5: DNA gets damaged over time so fresh, new cells – built by faulty instructions – aren’t (as) good. That’s how you get wrinkles and weak bones and such. And one day you’ll get catastrophic organ failure, which we usually mean by “natural death”. Like new heart muscle cells just not being enough to do the job, and such.
Main thing that’s damaging DNA (and thus slowly killing us) is oxygen, but diet, pollution, lifestyle and such is also a factor.
A lot of factors play a role in aging, but an important one that’s easy to understand is telomere shortening. As you may know, the process of transcription transcribes DNA into mRNA to take to the ribosome to be the blueprint for your proteins. Most of this DNA gets transcribed perfectly; however, your RNA polymerase isn’t that great at reading the ends of DNA strands (called telomeres). So, your body has to use telomerase to artificially lengthen the ends of your DNA strands, so that the RNA polymerase can finish reading them. Over time, our telomerase doesn’t do its job right every now and then, and just that little bit of DNA strand gets lost and doesn’t become proteins. On a long enough timeline, that leads to the body missing a fair amount of proteins that it needs, and this has a noticeable affect on aging, especially in the brain.
Interestingly, studies are now also finding that artificially giving extra telomerase to mice has caused their brains to slow down the aging process, which has huge implications for diseases like Alzheimers.
By design.
Species that don’t have the previous generation make way for the younger one never develop or evolve. So most species have one way or another of getting rid of the old farts. Mostly that means [telomeres](https://en.wikipedia.org/wiki/Telomere) at the end of your DNA that snap off when they get copied. You’ve got something like 1500 base pairs of just garbage non-encoded DNA data at the end. Every time a cell splits it snaps off 3-12. When you get really old and your skin and hair cells (which replicate a lot) run out of telomeres, they KEEP SNAPPING OFF DNA and digging into more important stuff. “Old age” is when your cells start to lose the code needed to function.
Lobsters don’t do that. When they get too big and too old, they can’t physically remove their shell to molt and they essentially suffocate trapped in their old skin. If they’re aided when they molt, we don’t know how long they could live.
Liz Parrish, the CEO of BioViva experimented with gene therapy to add more telomeres to the end of her DNA. I don’t think it worked.
Each time a cell undergoes [mitosis](https://en.wikipedia.org/wiki/Mitosis), the [telomeres](https://en.wikipedia.org/wiki/Telomere) on the ends of each [chromosome](https://en.wikipedia.org/wiki/Chromosome) shorten slightly. Cell division will cease once telomeres shorten to a critical length. Hayflick interpreted his discovery to be aging at the cellular level. The aging of cell populations appears to correlate with the overall physical aging of an organism
The max number of times a cell can do this is called the hayflick limit.
[https://en.wikipedia.org/wiki/Hayflick_limit](https://en.wikipedia.org/wiki/Hayflick_limit)
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