Summary
A triplet of mRNA bases that codes for one amino acid or a stop signal.
In depth
The third base of a codon often tolerates changes (wobble), so many mutations at this position are silent. Codons such as UUU code for phenylalanine, and AUG for methionine.
Codon usage varies among species and affects translation speed, important when designing synthetic genes.
Codon bias differs between species and genes: highly expressed genes use codons matched to abundant tRNAs. This matters in biotechnology, where a human gene expressed in bacteria may be made poorly unless it is codon-optimised. Synonymous mutations can still affect folding speed and mRNA stability, and so are not always silent.
A reading frame is set by the start codon; three possible frames exist on each strand, giving six in total. Overlapping genes occur in viruses and bacteria, where a single stretch of DNA is read in two frames.
Example: the sequence AUG GCA UUU reads as methionine, alanine, phenylalanine, and shifting the frame by one base gives a completely different peptide.
Frequently asked questions
What is Codon?
A triplet of mRNA bases that codes for one amino acid or a stop signal.
Which area of biology covers Codon, and how advanced is it?
Codon is one of the 52 topics in Molecular Biology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Start and Stop Codons, Genetic Code, Transfer RNA.
Can you give an example of Codon?
Changing UAU (tyrosine) to UAA creates a stop codon.
What should I learn before Codon?
Codon is a Beginner topic, so no earlier topic is required. Other Beginner topics in Molecular Biology that pair well with it include Central Dogma, DNA Replication, Base Pairing.
What topics are related to Codon?
The closest topics to Codon are Start and Stop Codons, Genetic Code, Transfer RNA, Wobble Hypothesis. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Codon?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Codon. To practise the whole of Molecular Biology, use the Molecular Biology quiz.
How is Codon different from Start and Stop Codons?
Codon: A triplet of mRNA bases that codes for one amino acid or a stop signal. Start and Stop Codons: AUG begins translation and codes methionine; UAA, UAG and UGA end it. Read both side by side and note what each one explains.
How should I study Codon step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Start and Stop Codons and explain the difference aloud. Finally, take the Molecular Biology quiz and come back to this page for any question you miss.