No matter whether you are a bacterium in someone's mouth, a house plant, a pet cat, or a mushroom about to be cooked for dinner, the relationship between the sequence of nucleotides in each codon and the amino acids they specify is essentially universal. The genetic code is this relationship. Some amino acids such as methionine are encoded by a single codon while other amino acids are encoded by up to six codons. Three codons don't encode any amino acid and are termed "stop codons" because they occur at the end of a coding region. At first glance it is obvious that the relationship is not random. Upon further examination more patterns emerge. For example, in the first column of the table (link above) all of the codons contain a uracil in the second position and most encode amino acids that are hydrophobic: Phenylalanine, Leucine, Isoleucine, and Valine.

Questions:Why does this order exist? Hint: What are the consequences to proteins if amino acids are changed by mutations in the DNA?

8/22/04 Copyright (C) 2004, Jonathan Monroe, monroejd@jmu.edu. All rights reserved.
URL: http://csm.jmu.edu/biology/courses/bio220/qotw7.html