Previously we saw how DNA is formed, from the Nucleotide "monomer" units to the full double helix structure of the polymer.



DNA exists as coiled polymer, eventually making up the chromosomes in the cell nucleus. DNA holds the information needed to make proteins. The "recipe" or "instructions" for a particular protein is held in "segments" of DNA in the chromosome, called "genes".


Each gene is responsible for making a specific protein. Proteins are made by stringing together substances called “Amino Acids” in a certain order. The order is contained in the gene.


Bases are grouped in THREES, the sequence of bases (GTC in this case) “codes for” (or directs) a certain Amino Acid. 



Valine in this case (GTC)


There are only 4 bases (Uracil replaces Thymine in the mRNA – see later) and only 20 Amino Acids are created in the human body (coded for in the human genetic code, although over 500 exist).


The number of ways that we can make a 3-CODON (3 base selection) from the 4 bases available is given by a fairly simple formula:



64 possible “triples” out of 20 Amino Acids means that sometimes the same Amino Acid can be coded from different 3-CODONS. 


A codon chart shows the permutations of bases and the Amino Acids coded for. 



Reading from the inner to outer circles reveals the Amino Acid coded for, eg: UCU codes for Serine.