Genes are the complete DNA instructions for the construction of a protein. Each gene is composed of groups of three nucleotides called codons. Each codon instructs the cell to add a particular amino acid to the assembling protein.
Each protein is made of as many as 20 possible amino acids. There are, however, 64 possible codons. This means that many amino acids have more than one codon that represents them, and even single genes sometimes call for the same amino acids with different codons. Only two amino acids, tryptophan and methionine, are represented by a single codon.
Proteins are absolutely crucial to all forms of life and make up as much as 50 percent of the dry weight of a cell. Proteins are the molecules that compose most cellular machinery. They also form the backbone of DNA and RNA molecules. Proteins are large and complex molecules that must be built very precisely. Their functions depend not only on their basic chemical sequence, but also in how they fold, exposing or hiding various reactive portions to their environments.
A protein is coded not only to act on its environment, but to facilitate bonding and repulsion from various parts of itself. These specific and intricate functions are why genes are so crucial, and mutations can be so harmful to an organism.