Over the years, scientists have learned a lot about DNA. Nevertheless, the molecule continues to surprise us with its exquisite design. Not long ago, scientists demonstrated that a single gram of DNA can store about 500,000 CDs worth of information. It has also been shown that the code used by DNA to store this information has been specifically designed to allow living organisms to respond to their environment in many different ways. In addition, we know that DNA stores its information in “modules” that can be rearranged in many different ways. This allows a single stretch of DNA to contain many different meanings, depending on how the modules are put together.
In the December 13 issues of Science, researchers have demonstrated yet another incredible design feature of DNA, and according to the University of Washington, the scientists who made the discovery were “stunned.” To understand what was done and what the discovery means, however, you need a little bit of background information on DNA and how it is used by the cell.
DNA stores its information in sequences of nucleotide bases called adenine (A), thymine (T), guanine (G), and cytosine (C). As shown in the illustration above, those nucleotide bases link together to hold DNA in its familiar double helix shape. The meaning of each sequence depends on where it is in the molecule. In many organisms, a small fraction of the DNA is made up of genes, and in most of the organisms with which you and I are familiar, the genes consist of two regions: exons and introns. The exons of a gene contain the recipe that tells the cell exactly how to make a protein. This recipe is given in groups of three nucleotide bases, which are called codons. Each codon specifies a certain chemical called an amino acid. When the cell stitches amino acids together in the sequence given by the codons, it makes a useful protein.
Introns are “spacers” that exist between the codons in a gene. Once derided by evolutionists as “junk DNA,” we now know that introns are a powerful means by which the exons are split up into functional information modules. The cell can stitch the modules together in different ways, so that a single gene can instruct the cell on how to make many different proteins. This is called alternative splicing, and it is a incredibly powerful design feature that allows DNA to store its information with amazing efficiency. Indeed, thanks to alternative splicing, there is a single gene in fruit flies that can tell the cells to make 38,016 different proteins!1
Now don’t get lost in all the terminology. Think of it this way: genes tell the cell how to make proteins. However, to increase the information storage capability of DNA, these genes are split into two regions: exons and introns. The introns separate the exons into modules of useful information, and the cell stitches those modules together in different ways so that a single gene can tell the cell how to make lots and lots of different proteins.
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