Thursday, September 23, 2010
Learning to Spell
Now that you have learned the genetic alphabetic A, C, G, T, and sometimes U, it is time to figure out how to spell using these letters. Like any spelling word, you have to use the letters of the alphabet to spell any word that makes sense. How many letters of our alphabet are needed to make a word? Well let's see. If each letter made a word, then you would only have four words. Certainly not nearly enough to spell 20 amino acids. Taking two letters at a time in any combination would only give 16 words. [You can try combining two letters in any order and see what you come up with.] Now if you take three letters at a time, combine them in any order, you would come up with 64 possible combinations. This would certainly give enough words to spell our 20 amino acids. As it turns out, that is exactly what our DNA figured out on its own. Taking three of our letters (nitrogenous bases) they were able to spell "amino acid". Combing these letters three at a time, in different order, spells each amino acid! What a deal. These three letters (nitrogenous bases) are now called a "codon". Thus our "Genetic Code" is made up of these "codons" lined up in sequence to tell us what to do. Each cell contains its own directions in the nuclear DNA. They tell the cell which amino acids to hook together in what order, and how many to join together in our polypeptide chain. [Remember poly=many, peptide=amine=nitrogen bound] chain. This chain becomes a protein.