There are 20 naturally occurring amino acids, therefore, there are only 20 mRNA codons. True or false

False. There are 20 amino acids, but 64 possible codons.

Explanation:

Genetic information for the aminoacids assembly during the protein synthesis is stored in short sequences of three nucleotides named codons in the mRNA. Each of the codons represents one of the 20 amino acids used to build the protein. The total number of possible codons is 64, from which 61 codify amino acids -more than one codon codify for the same amino acid-. One of these amino acids is also the start point of protein synthesis. And the left three codons are stopping translation points.

The codons indicating the initiation or stop points during the translation process are:

•The start codon AUG is the most common sequence used by eukaryotic cells and places near the 5´extreme of the molecule. However, other codons might be used as well. Prokaryote cells might use the codons GUG or UUG.

•The end codons are UAA, UAG, UGA.