This Demonstration shows the construction of a polypeptide in a ribosome, the process known as DNA translation. The mRNA contains a nucleotide sequence. Every group of three nucleotides on the mRNA is called a codon. Each tRNA carries an amino acid and has three nucleotides called anti-codons. As the mRNA passes through the ribosome, its codons match with the anti-codons of incoming tRNA, which release their amino acids. This chain of amino acids constitutes a polypeptide.