How do you ensure that a piece of genetic code produces the desired protein and not a multitude of others. How do you keep junk DNA from becoming active and causing undesired proteins from being produces.

Expert response from Community Manager

Moderator for GMOAnswers.com

Thursday, 30/01/2014 00:13

Great question. Alan McHughen, CE biotechnology specialist and geneticist, provided a related response that might be of interest to you; an excerpt is below:

“Genes are composed of long stretches of DNA, which is composed of the chemical building blocks we abbreviate as A, T, C and G (adenine, thymine, cytosine and guanine, respectively).  Just as in the human language English, in which thousands of words are composed of specific sequences of 26 letters, in biology all genes in all species are made of specific sequences of the four DNA bases, A, T, C and G.  The human insulin gene consists of 4,044 of these bases, beginning with―ATGGCCCTGTGGATGCG―at the start of the insulin recipe.

"When the plant, animal or microbe is "expressing" a gene to make the requisite protein, it reads the DNA three letters at a time. Each three-etter "word" in DNA specifies a particular amino acid―of which there are 20 different kinds floating around in the cell―and these amino acids serve as building-block ingredients for proteins.  As the gene sequence is read by the cell’s kitchen machinery, amino acids are strung together like beads on a string, called a polypeptide chain. Thus, the first part of the DNA recipe, ATG GCC CTG TGG ATG CGC, translates to the amino acids (in order) methionine, alanine, leucine, tryptophan, methionine, arginine, and so on, until the entire sequence of 102 amino acids is completed. The string of amino acids is processed in the cell to release functional insulin.

"Therefore, when engineers insert a known DNA sequence into a plant animal or microbe, the resulting 'expressed' string of amino acids in the protein will correspond to the recipe as provided in the DNA base sequence. This is true regardless of the species source, or the species recipient, as all living things use the same DNA language.

"To ensure the inserted gene does what it is supposed to, various molecular, chemical and biological tests are conducted on the GM plant, animal or microbe to check that the inserted DNA sequence is intact and the expressed protein is functional before the GMO is commercialized.  They are also extensively tested for safety and efficacy for several years prior to commercial release to ensure there are no unexpected or unusual results.

"There are no known examples where a specific gene recipe (DNA sequence) was inserted into a cell and produced something other than the predicted protein.  What can―and does―go wrong is when the inserted gene goes unexpressed, or is only partially expressed, such that the amount of protein is insufficient to prove commercial levels of the desired trait.  In those cases, the GMO is destroyed as soon as it is detected, usually in very early testing, and in any case long before commercialization.”

The full response is available here. If you have any additional questions, please ask.