What is the Genetic Code?
Before we can understand the genetic code, we must first understand some basic genetics.
Genes and proteins are written in different "languages." Genes are encoded within DNA, which are made of nucleotides, while proteins are constructed out of amino acids. In order for a biological cell to make proteins, the genetic information from DNA has to be translated.
First, the gene encoded in DNA is transcripted into a single strand of mRNA (messenger RNA). This happens inside the cell nucleus in eukaryotes. DNA and mRNA are both sequences of nucleotides. In DNA, the nucleotides are adenine, guanine, cytosine, and thymine. In RNA, the thymine is replaced with uracil, but otherwise the sequences are the same.
The mRNA then moves outside the nucleus to the ribosomes (rRNA), where protein synthesis takes place. Ribosomes move along the mRNA strand, reading it three nucleotides at a time. At each three nucleotides, called a codon, a molecule of tRNA (transfer RNA) binds to them.
There are several dozen different kinds of tRNA. Each can bind to a different codon at one end, and one of twenty amino acids at the other end. The tRNA brings amino acids to the ribosome as the ribosome reads the mRNA, and the amino acids are joined together to make a polypeptide, which later folds into protein.