What is a codon and why are they important?

What is a codon? How many nucleotides make a codon? Why are there three instead of two or one?

• Answer:

  A codon is, according to the Campbell Reece AP biology textbook, "a three nucleotide sequence of DNA or mRNA that specifies a particular amino acid or termination signal; the basic unit of the genetic code." Therefore 3 nucleotides make a codon. there are three because there are twenty amino acids since there are four choices of nucleotides (adenine, guanine, cytosine, and uracil) and there are three nucleotides in a codon, 4*4*4=64, which is more than 20 amino acids and therefore can code for all of them. however if it were 2, it would be 4*4=16 and is less than twenty. for 1, there would only be 4 possibilities of codons, which cannot possibly code for 20 amino acids.