Expert: Dana Krempels, Ph.D. - 12/3/2007

Question
I understand that DNA understands information in the form of codes using ACTG and that these codes can be rearranged and used to make thousands of different codes; one for hemoglobin, insulin, ect... and that these codes can be unzipped to recreate itself using half of the original. My question is, where does the particular information come from that says this specific sequence of codes is insulin thus enabling DNA the BLUEPRINT to DUPLICATE it? Or in other words, is it known where the "code" of the code that ACTG uses to make hemoglobin comes from?

Answer
Dear Brad,

Your question is a little bit difficult to decipher, but I'll do my best.

I think the problem is that your understanding of the DNA code isn't quite accurate.

The four-"letter" code of the DNA proteome (the DNA sections that code for proteins; not all of it does) is written in the form of *codons*.  Every three letters (one codon) on the DNA strands represents one amino acid to the cell mechanisms that construct protein.  A protein is a long chain of amino acid subunits, and the order of the specific amino acids of a protein will determine its identity, its chemical and physical properties, and what its final destination in the cell and body will be.

There is not a single gene that codes for insulin or a gene for hemoglobin.  But there are genes that encode the *component* proteins of those complex substances.  

Once a protein is manufactured at the ribosome (this process is called translation), it is transported to the Golgi Apparatus, a cellular organelle where proteins and other substances are put together to make more complex substances such as hormones, hemoglobin, insulin, neurotransmitters, etc.

The "factory" the cell uses to construct these things is a series of very specific enzymes--proteins (also encoded by their own genes in the DNA) that act as "assembly line" workers to link proteins together and with raw materials to make finished products.  These are then packaged into membrane-bounded vesicles (little sacs) that move to the plasma membrane of the cell and are exported for transport via the bloodstream or other means to where they will be used by the body.  Or sometimes they're used right there in the same cell; it depends on the finished product and its final function.

How does the cell know which proteins should become part of hemoglobin, and which part of insulin, etc.?  We are just now starting to understand this, but the secrets are not all known yet.  It has to do with specific enzymes and how they are activated and controlled, and this may turn out to have a lot to do with a relatively newly discovered class of nucleic acids, microRNAs, which act almost like cellular "conductors"--orchestrating all the other genetic and construction activities of the cell.  It's a very interesting time to be learning about genetics!

Hope that helps make it a little bit clearer.

Dana