Does our DNA material come from our diet

[Wesley_Clark]

DNA is made of nucleotides (and sugar and a phosphate). Do the nucleotides come from our diet or are they built inside of us from other chemicals we get from food? Is my DNA built from the nucleotides in some bacon I ate when I was 9 or is it built from scratch from the atoms?

[Broomstick]

I think it’s built from the amino acids found in the protein we eat.

[Squink]

nucleotide biosynthesis

The pathways for the biosynthesis of nucleotides fall into two classes: de novo pathways and salvage pathways (Figure 25.1). In de novo (from scratch) pathways, the nucleotide bases are assembled from simpler compounds. The framework for a pyrimidine base is assembled first and then attached to ribose. In contrast, the framework for a purine base is synthesized piece by piece directly onto a ribose-based structure. These pathways comprise a small number of elementary reactions that are repeated with variation to generate different nucleotides, as might be expected for pathways that appeared very early in evolution. In salvage pathways, preformed bases are recovered and reconnected to a ribose unit.

I’m not certain of this, but I think that the salvage pathway works only on nucleotide bases already in the body, and that ingested nucleic acids get broken down in the stomach and small intestines. I do know that most ingested nucleic acids get broken down, but perhaps not 100%? The presence of high concentrations of nucleic acids is one of the reasons that single-cell-protein (bacterial paste) never caught on as a human food source. The nucleosides are broken down into uric acid, which can bring on Gout.

[Colibri]

@Broomstick

I think it’s built from the amino acids found in the protein we eat.

Other way round. DNA does not contain amino acids, but rather nucleic acids. DNA provides the instructions to assemble amino acids into proteins.

[edwino]

Broomstick kind of is right, though. Aspartate and glutamine (amino acids) are used IIRC as the nitrogen sources in de novo nucleotide synthesis.

[Josh_dePlume]

Yes, Broomstick is absolutely right about the nitrogen atoms (and some of the carbon atoms) in nucleotides coming from amino acids. And although mRNA serves as a template for protein synthesis, it is not a precursor of protein; the atoms in the mRNA don’t wind up in the protein. The arrows in DNA->RNA->protein should not be interpreted the way they are in chemical reactions.

[Colibri]

@edwino

Broomstick kind of is right, though. Aspartate and glutamine (amino acids) are used IIRC as the nitrogen sources in de novo nucleotide synthesis.

Well, OK, but that’s indirect. It seemed to me that Broomstick’s answer implied that DNA actually contained amino acids, which it doesn’t.

[easy_e]

from [Digestion of nucleic acids](http://www.biologymad.com/Digestion/Digestion.htm#Digestion of Nucleic acids):
-Pancreatic nuclease enzymes digest nucleic acids (DNA and RNA) to nucleotides in the duodenum.

-Membrane-bound nucleotidase enzymes in the epithelial cells of the ileum digest the nucleotides to sugar, base and phosphate, which are absorbed.

So it looks like this is the source of the bases in the salvage pathway Squink’s link mentioned.