Spreadsheets in Molecular Biology

Abstract

The central dogma of biology is that deoxyribonucleic acid (DNA) makes ribonucleic acid (RNA) makes protein (Alberts et al. 1994; Lodish et al. 1995). The DNA molecule is a simple linear chain each link of which contains one of four different chemicals called bases. These bases are adenine, thymine, guanine and cytosine and are usually abbreviated as A, T, G and C respectively. Since any one of these bases can be found at each link in the chain the potential informational content of even short lengths of DNA is enormous. For example, a modest twenty base DNA segment can be constructed in 420 different ways, corresponding to 1.099 x 1012 combinations. In living cells segments of DNA generate complementary RNA molecules with the same information content. Certain of these RNA molecules are used to direct the production of proteins. Appropriate parts of the RNA sequence are read in sets of three bases, called codons. The 64 (4*4*4) possible codons each have a specific meaning, resulting in the addition of one specific amino acid to a growing protein or the ending of that chain. Like nucleic acids, proteins are also linear chains, with each link in the chain being represented by one of twenty different types of amino acid. The potential informational content of protein sequences is even greater than nucleic acid sequences. For example there are 2010 = 1.024 * 1013 possible 10-amino acid peptides. The specific nucleic acid sequence is therefore decoded into a specific protein sequence, which in turn defines the folded three-dimensional structure and positioning of chemically reactive amino acid side chains on this structure, both of which determine the function of the protein.