#you can't age if your cells are repaired as quickly as they're damaged.

[camerica]

[saltierthanbottomofapretzelbag]

@asian-high-faerie Hi! Not a bother at all! I love talking about this!!! and I just had a two hour "review" session today on DNA damage and repair (yay medical school.) so I was stoked to see this! ��

So, as I mentioned above in an edit, telomerase is turned on in highly mitotic cells (cells that divide alot): T cells, B cells, the epidermis, and stem cells, for example. So to modify your first question just a bit: why not turn telomerase on in all cells?

The short answer: Cancer.

The long answer: As cells go about their day to day lives, they pick up DNA damage. There are all kinds of things that can damage DNA: UV radiation, carcinogen exposure, random mistakes by DNA Pol (which, after proofreading, makes a mistake every 10^6th base pair), some viruses, tautomerization. And that's just off the top of my head. So damage to DNA sounds bad, but the cell has a whole suite of repair enzymes that can repair DNA damage. So we're good right?

Wrong. Those enzymes need a template to work with, which isn't always available so sometimes the repair enzymes randomly insert stuff or blindly join two ends.

So over time the cell starts to accumulate mutations, which are basically typos. And for the most part that's okay. Not all DNA codes for important things (like protein, ribosomal RNA, tRNA), so mutations to the "less important" DNA (silenced genes, introns, non-vital proteins) don't really matter. Just like a typo in the copyright page of a book won't bother most readers or affect their enjoyment of it. But over time, as the mutations build up, it does start to matter.

For example:

There you are.

Theree you are.

Theree yo are.

Three yo are.

Three yo re.

At some point, it becomes unreadable. Cells don't want to let it get that far so they're programmed to die before then.

Why don't they want it to get that far? Because if you accumulate enough mutations to the right genes (proto-oncogenes), you can started dividing uncontrollably and stelaing nutrients from your neighbors. And crongratulations, you are officially a cancer cell!

So cells are programmed to die (hopefully) before that happens. Their telomeres run out, they undergo apoptosis, ect. We call this programmed senescence. It's a mechanism designed to minimize the number of cells that turn into cancer cells.

The medium length answer: Cell don't have telomerase activated because of an adaptation called programmed senescence, which is an important barrier to the genesis of cancer cells.

Now, on to your second question!

If we find a way to activate them, will we stop aging?

The short answer: Technically. But you're probably going to die of cancer.

The long answer: It's a little more complicated than that. Sure the person probably wouldn't age in the way that we think of aging. But they also wouldn't live forever. They'd probably die of cancer. How quickly they get cancer (or at least one we can't cure) would just be luck of the draw. Maybe they don't get mutations anywhere critical. But probably they will. It's just a matter of time. So if you want to stop aging in any sort of a meaningful way, then you ALSO need to find a way to deal with all the mutations that are accumulating in the newly immortal cells.

Because with an infinity to live, the cells are going to make mistakes. And the wrong mistake to the right gene might just kill you.

A thought about aging

So we have characters in SJM books who can get very old but still look young. Then we have Dumbledore who lived to be 170ish (if I’m not mistaken) and he aged physically….so like what could be a scientific difference….how do some grow old but dont look it and how do some look older but are still young compared to the others….