atom replacement in human cells - (Nov/13/2013 )

I have read that, though most of the cells in the human body are constantly being replaced, we keep most of our brain cells throughout life. However, are individual atoms being replaced in brain cells? I other words, while the specific brain cell continues to exist, are the individual atoms comprising that cell gradually being replaced? Are individual atoms replaced in cellular DNA? Quantum physics tells us that atoms are popping into and out of existence all the time.

I guess you won't have much success here as biologists rarely work on single atoms and its replacement (you have to use isotopes and see how they distribute in the body such as it is mentioned here ). Today you won't do that anymore except perhaps on some lab animals, but since research topics of life sciences have a different focus and methods, I think almost nobody works on such questions anymore, as the results are more or less known and are of only academic interest.
And finally just do this and you'll find many websites discussion this.

Since you brought up quantum physics, you should be aware that all atoms (of the same isotope) are indistinguishable. It actually makes no sense to ask if one atom has been replaced by another, since you can't tell, even in principle.