Translation is the process by which the information contained within mRNA is used to synthesize proteins. The process involves ribosomes moving along mRNA to translate its nucleotide sequence into a polypeptide sequence. Triplets of nucleotides (groups of three bases; see the image below) called codons specify which amino acid will be added to the growing polypeptide chain.
On mRNA, there are three types of codons: start codons, which signal where translation should begin; stop codons, which signal where it should end; and codons that specify which amino acid should be inserted. The start codon is AUG, which codes for the amino acid methionine (Met). There are three stop codons: UAA, UAG, and UGA.
During translation, transfer RNA (tRNA) molecules carry specific amino acids. The tRNA has an anticodon that is complementary to the mRNA codon, allowing it to bind. This allows the correct amino acid to be added according to the mRNA sequence.
DNA must first be transcribed into mRNA before translation can occur. The DNA double helix unwinds and mRNA is synthesized in a process complementary to the DNA nucleotide sequence.
Because DNA uses base pairing, a G matches with a C, and an A matches with a T. Therefore, when RNA polymerase reads DNA to make mRNA, it incorporates a base that is similar to but different from T — U replaces T and, like T, it pairs with A (see the image below). This produces mRNA with a sequence complementary to one DNA strand, which the ribosome can then read to direct the production of an amino acid chain (polypeptide) that will eventually become a protein.
