how many possible codons are there

There are 64 possible codons in the standard genetic code.

What is a codon?

• A codon is a sequence of three nucleotides in DNA or RNA that specifies either an amino acid or a stop signal during protein synthesis.

• Because codons are read in triplets, each “word” in the genetic code is three nucleotides long.

Why exactly 64 possible codons?

• There are 4 nucleotide bases (A, U/T, G, C), and codons are triplets, so the total number of combinations is 43=644^3=6443=64.

• These 64 codons include 61 that code for amino acids and 3 that function as stop signals.

How those 64 codons are used

• Multiple codons can encode the same amino acid, which is why 64 codons correspond to only about 20 standard amino acids.

• Three codons (UAA, UAG, UGA) act as stop codons, signaling the end of translation rather than adding an amino acid.

TL;DR: With four bases taken three at a time, the genetic code has 64 possible codons, of which 61 code for amino acids and 3 serve as stop signals.