The Magic Molecule

Before delving completely into synthetic biology, I feel that it is important to discuss DNA. After all, DNA is a synthetic biologist's medium. Had it not been for the work of some very clever scientists in the first half of the 20th century, it would not be possible to do synthetic biology.

Biologists have known about DNA's existence since 1869, when Johann Friedrich Miescher isolated an unknown material from white blood cells collected from the pus on discarded bandages. This substance came to be known as deoxyribonucleic acid, or DNA. Over the years DNA's role as the carrier of genetic information was gradually established by famous experiments such as Oswald Avery's work with Streptococcus pneumoniae in the 1940s. However, James Watson and Francis Crick are the scientists most often associated with DNA. They shared the Nobel Prize with Maurice Wilkins in 1962 in part for their discovery of the structure of DNA, which was published in Nature in 1953. Rosalind Franklin died before she could be considered for the prize, and some allege that she was denied the recognition she earned during her lifetime because of her gender. Science is a human endeavor, after all, subject to the prejudices and whims of its practitioners.

Today we know quite a lot about DNA. We know its famous double helical structure, how it copies itself to give rise to progeny cells, and what its letters mean. When people talk about nucleotides, bases, or base pairs, they are referring to the letters G, C, A, and T. These letters are abbreviations for the chemicals guanine, cytosine, adenine, and thymine. These chemicals combine into enormous chains called DNAs.

But what's the good of knowing an alphabet without knowing the language it builds? The real power of DNA comes from the genetic code. In DNA's language, every word is made of three letters. Biologists call these "words" codons. Since there are 4 different bases and each codon contains three, there are a total of 4³ or 64 codons. Cells have evolved elaborate and reliable machinery to read these codons. But what is the purpose of all of this? It's actually quite simple. The instructions encoded by DNA are used to build proteins, which carry out all of the functions of a cell: breaking down food, communicating with neighboring cells, keeping track of night and day, coordinating reproduction, and endless others. Each of the 64 codons correspond to a particular instruction. One codon tells the cell's machinery to start building a protein. Three others tell it to stop. The remaining 61 specify which amino acid—the units used to build proteins—to add at a particular point in the protein chain. A gene can roughly be defined as the DNA instructions for making a particular protein.

Synthetic biology uses DNA-based devices to perform desired functions. For example, by placing the gene for human insulin into yeast we are now able to provide insulin for diabetics that is identical to what the body naturally produces. Insulin was previously only accessible by extracting it from pigs and cows.

DNA is such a fundamental and beautiful part of life as we know it because its instructions are what allow life to exist, to evolve, and to produce the stunning diversity that we observe in the natural world.

Image Credit: Adapted from PDB file 1BNA.

References and Further Reading:

Campbell, A.M. What is Synthetic Biology? (2009).

Judson, H.F. The Eighth Day of Creation: Makers of the Revolution in Biology. Twenty-Fifth Anniversary ed. Woodbury, NY: Cold Spring Harbor Laboratory Press, 1996.

Research Collaboratory for Structural Bioinformatics. Protein Data Bank (2011).

Watson, J.D. & Crick, F.H.C. Genetical Implications of the Structure of Deoxyribonucleic Acid. Nature 171, 964–967 (1953).

Watson, J.D. & Crick, F.H.C. Molecular Structure of Nucleic Acids: A Structure for Deoxyribose Nucleic Acid. Nature 171, 737–738.