Codon
Say it: KOH-don
A codon is a sequence of three nucleotides in DNA or messenger RNA that stands for one amino acid or tells the ribosome to stop.
Also: codons
Definition
What is a codon?
A codon is a group of three neighboring bases in messenger RNA, or in the DNA it was copied from, that a cell reads as a single instruction while building a protein. Each position can hold one of four bases, which gives 64 possible codons. Of these, 61 stand for amino acids, and the other three (UAA, UAG and UGA) are stop codons that end the chain.
Ribosomes read messenger RNA codon by codon, beginning at AUG, the start codon, which also codes for methionine and sets the reading frame. Transfer RNAs carry anticodons that pair with each codon and bring the matching amino acid. The code is redundant: most amino acids have several codons, and these usually differ only in the third base, so some single-base changes leave the protein unchanged. Inserting or deleting bases in a number that is not a multiple of three shifts the reading frame and garbles every codon after it.
Nearly all organisms share the same codon table, strong evidence that life has a common origin. Students use it to translate sequences by hand in genetics problems.
Word parts
Where does the word “codon” come from?
- cod-
- codeEnglish code, from Latin codex, book
- -on
- a basic unitscientific suffix, as in electron
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Related
Terms that go with it
- Messenger RNAMessenger RNA is the RNA copy of a gene that carries protein-building instructions from DNA to the ribosomes, where it is read in three-base codons.
- Transfer RNATransfer RNA is a short adaptor RNA that brings a specific amino acid to the ribosome and pairs with the matching mRNA codon through its anticodon.
- TranslationTranslation is the process in which a ribosome reads the codons of a messenger RNA and links amino acids in that order to build a protein.
- Amino acidAn amino acid is a small organic molecule with an amino group, a carboxyl group and a side chain; amino acids link together to form proteins.
- RibosomeA ribosome is a molecular machine of RNA and protein that reads messenger RNA and joins amino acids in the order it specifies to build a protein.
- Frameshift mutationA frameshift mutation is an insertion or deletion of DNA bases, in a number not divisible by three, that shifts how the rest of a gene's codons are read.
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