Why does cell division at unicellulars prolong life?

[mr02077]

Why would cell division be a mean that prolongs life of a unicellular?

In many encyclopedias you can read life is mortal due to multiple reasons (mutations in nuclear and mitochondrial DNA, DNA methylation, shortening of telomeres, accumulation of waste material and free radicals). All those negative impacts are accumulated in a cell mass that is to divide, so from my standpoint, division would be just splitting in two material that would be equally close to death in the life path, as it was before the division.

I do not see what is rejuvenating in cell division, as we here talk about mitosis of unicellulars (almost no gene recombination to revitalize the gene pool and it is not like cell multiplication in multicellulars that obviously helps to regenerate tissues)

Thank you for spending time to give your input !
 

[CharonY]

Can you provide the context in which cell division would be considered rejuvenation? There are some mechanisms but  I am not sure whether these are cases you may be thinking about.

[mr02077]

Here I was thinking strictly about reproduction of unicellulars and the extension of life facilitated in that way. 

If a unicellular organism does not divide (reproduce) it will die. The reproduction, in contrary, extends life for endlessly long.

[CharonY]

Well, that is getting the causality wrong, in my opinion. For the most part unicellular organisms have the tendency to replicate which is why cells that are not replicating are often at the end of their life cycle and do not successfully divide anymore. Even then this is not strictly correct, as certain cell types care able to undergo dormancy. What is rare is to have a very active metabolism but not reproduce, as the former often serves the latter. In addition, there is the intricate interaction between metabolism and replication as the major drivers for aging.

The mechanisms I was thinking about is inequal division in which the resulting daughter cells obtain a different share of components. Here, real rejuvenation can happen by having one daughter cell obtain all the damaged elements (examples in yeast include e.g. ROS damaged mitochondria) whereas the other obtains the "fresher' parts so that one daughter cell has less damage than the parent cell.

[mr02077]

Thank you @CharonY , for this reply from more than a month ago.

I am still wrecking my brain on this. Maybe I have connected the dots wrongly, but to me it seems simple - if you look at protists or bacteria, with binary fission or mitosis they reach an endless lifeline.

Not like soma of eukariotic multicellulars that dies and gets rejected, while only germ cells continue living.

And even with the dormant cells - those die after some limited time, inevitably, and in most cases lots before the whole of the organism,and do not continue the lifeline.

Your answer seems like just perceiving direct link between active replication and life continuation - but does not go casually below it.

To me it seems obvious that the whole process of replication contains something rejuvenating (on the example of unicellulars) as the same line of body mass is the acter. Maybe it is just the growth of new fresh body mass, during the interphase.

Otherwise a dormant cell that stop replication just dies fom one of the reasons.

I do not know...

Edited June 22, 2019 by mr02077

[Endy0816]

Germline cells and select others have access to telomerase. Allows them to re-lengthen their telomeres and continue replicating indefinitely.

The vast majority being 'mortal' via going into senescence is thought to help prevent cancer.