The nucleotide sequence in the DNA is first transcribed into a molecule of messenger RNA (ribonucleic acid). The RNA, using a slightly different code (represented by the letters A, C, G, and U, the last letter… These three-letter words are called codons.

A codon is a trinucleotide sequence of DNA or RNA that corresponds to a specific amino acid. The genetic code describes the relationship between the sequence of DNA bases (A, C, G, and T) in a gene and the corresponding protein sequence that it encodes. The cell reads the sequence of the gene in groups of three bases.

Which of the following statements regarding codons is true? Explanation: Every codon is composed of three RNA nucleobases, and codes for a specific amino acid; however, there can be multiple codons that code for one amino acid. The start codon, AUG, signals the beginning of translation and codes for methionine.

The initial codon in the mRNA establishes the reading frame and defines the protein’s initial amino acid. Two amino acid residues, tryptophan and methionine, have unique codons—UGG and AUG, respectively. All other amino acids may be coded for by more than one codon, such that the code is said to be degenerate.

Listen to pronunciation. (KOH-don) In DNA or RNA, a sequence of 3 consecutive nucleotides that codes for a specific amino acid or signals the termination of gene translation (stop or termination codon).

Codons provide the key that allows these two languages to be translated into each other. Each codon corresponds to a single amino acid (or stop signal), and the full set of codons is called the genetic code.

AUG

Each three-letter sequence of mRNA nucleotides corresponds to a specific amino acid, or to a stop codon. UGA, UAA, and UAG are stop codons. AUG is the codon for methionine, and is also the start codon.

Operons are common in bacteria, but they are rare in eukaryotes such as humans. In general, an operon will contain genes that function in the same process. For instance, a well-studied operon called the lac operon contains genes that encode proteins involved in uptake and metabolism of a particular sugar, lactose.

It was thought that polycistronic transcription is a characteristic of bacteria and archaea, where many of the genes are clustered in operons composed of two to more than ten genes. Like bacterial operons, eukaryotic operons often result in co-expression of functionally related proteins.