What is a 3-nucleotide code on mRNA called?

Codon. The 3-nucleotide code on mRNA is called codon. Codon represents a sequence of 3 nucleotides that is part of genetic code. They are often seen in mRNA. Messenger RNA is the type of RNA produced during transcription. It carries genetic information from DNA to the ribosome. There are 64 codons. Each codon contains three nucleotides.

Sixty-one of the code for amino acids and 3 of them are called stop codons because they terminate the process of translation when present. The three stop codons are UAA, UAG, and UGA. They do not code for any amino acid, and when present, the ribosomes stop and fall off the mRNA. Although we have 61 codons that code for amino acid, there are only 20 amino acids known. This means about 2 to 3 codons code for the same amino acid sequence.