How can an old organism create a young one?

[Ovi]

I never understood this. :confused: Yes the DNA gets damaged and our cells accumulate all sorts of debris which is what causes senescence, but how come children aren't born with the same defects that makes us old? How come they are young? Why can't we create young cells to replace the old ones that we have? Is it related to natural selection, as in children who inherit the wrong mutations will be selected against in the outside world, but such genetic selection can't happen inside our body? Or maybe because neurons don't undergo cell division, thus they can't rejuvenate? But then again, our entire body ages, not only our brain.

And by the way how about cloning? Would that breed a young organism, or a prematurely aged one?

[bcbm]

miracles

[ÑóẊîöʼn]

I never understood this. :confused: Yes the DNA gets damaged and our cells accumulate all sorts of debris which is what causes senescence, but how come children aren't born with the same defects that makes us old?

Well, I've read that strictly speaking, they are. It's just that the signs of old age do not tend manifest themselves until one is past breeding age.


Why can't we create young cells to replace the old ones that we have?

Have you considered the possibility that the mechanism for creating new cells could itself experience wear and tear?


And by the way how about cloning? Would that breed a young organism, or a prematurely aged one?

If I remember correctly, Dolly the cloned sheep died young. However, I suspect it's different for plants, which are much easier to clone.

[mikelepore]

The most popular theory is that the telomeres at the end points of chromosomes get damaged, so that cells reproduce imperfectly, causing us to age. The process that produces eggs and sperm repairs truncated telomeres with the help of the enzyme telomerase.

[Ovi]

Have you considered the possibility that the mechanism for creating new cells could itself experience wear and tear?

Then how come newly born organisms don't experience the same wear and tear and aren't born old?

The most popular theory is that the telomeres at the end points of chromosomes get damaged, so that cells reproduce imperfectly, causing us to age. The process that produces eggs and sperm repairs truncated telomeres with the help of the enzyme telomerase.
In that case, why can't our body do the same repairing on other types of cells? It does on stem cells. Telomeres act to protect the cells from too much damage to its DNA by preventing the development of cancer. In that case how come newly born do not have the same defects that we do and don't have much higer odds of developing cancer? The question is how come we are subjected to processes that age us and our cells inevitably lose their functions, but at the same time can create young cells that have full function? What stops the body from using the same mechanisms for its own good?

[mikelepore]

Eggs and sperm don't come from a division of cells that age like the rest of the body. They come from progenitor cells, which have a failure mode, but a different kind of failure mode. Progenitor cells reach the point when they can't divide anymore. That determines how many reproductive years the individual will have, the ages of menopause and andropause. The limitations of progenitor cell division don't lead to defective reproductive cells.