Every three bases on DNA stands for ONE amino acid
Each three-letter unit on mRNA is called a codon
Most amino acids have more than one codon!
There are 20 amino acids with a possible 64 different triplets
The code is nearly universal among living organisms
Important features of the genetic code include:
Each codon consists of three bases (triplet). There are 64 codons. They are all written in the 5′ to 3′ direction.
61 codons code for amino acids. The other three (UAA, UGA, UAG) are stop codons (or nonsense codons) that terminate translation.
There is one start codon (initiation codon), AUG, coding for methionine. Protein synthesis begins with methionine (Met) in eukaryotes, and formylmethionine (fmet) in prokaryotes.
The code is unambiguous. Each codon specifies no more than one amino acid.
The code is degenerate. More than one codon can specify a single amino acid.
All amino acids, except Met and tryptophan (Trp), have more than one codon.
For those amino acids having more than one codon, the first two bases in the codon are usually the same. The base in the third position often varies.
The code is almost universal (the same in all organisms). Some minor exceptions to this occur in mitochondria and some organisms.
The code is commaless (contiguous). There are no spacers or “commas” between codons on an mRNA.
Neighboring codons on a message are non-overlapping.
Binod G C
I'm Binod G C (MSc), a PhD candidate in cell and molecular biology who works as a biology educator and enjoys scientific blogging. My proclivity for blogging is intended to make notes and study materials more accessible to students.
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