More on DNA vs. epigenetic information: the strong case for DNA

I understand PZ’s point, that the information in DNA is expressed through and requires the cell (cytoplasm, nucleoplasm, etc). But the cell is self-assembling–put a human nucleus in a mouse cell, let it divide a dozen times, (maybe a hundred times), and now you have completely human cell. Cloned animals have epigenetic-derived defects, but I expect their Nth generation offspring will be normal.

Let me push the argument further taking a bacterial cell as the model. In principle, you could express proteins in vitro and combine them with lipids, small molecules, and DNA and reconstitute a cell. It wouldn’t be quite right, but get it close enough that it can divide, let it do so a bunch of times and then the cell will be completely normal.

But which proteins would you express and how would you figure out how to combine them? In principle, you could predict from the DNA sequence the set expressed in a particular environment, relative expression levels, and where they go–membrane, cytoplasm, etc.

True enough, DNA without its cellular environment is not a cell, and in biological systems the DNA is always associated with its cell, but the epigenetic information is mainly derived from the DNA and secondary to it. For the biologist this distinction is meaningless–practically we can’t yet predict epigenetic context from DNA or recreate it from scratch. Biologists describe the epigenetic state, observe it and assay for it.

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