Why amino acids are essential?

Why does amino acids with similar chemical properties often have similar codons?

• One remarkable feature of the genetic code is that amino acids with similar chemical properties often have similar codons. For example...codons with U or C as the second nucleotide tends to specify hydrophobic amino acids. Can you suggest a possible explanation for this phenomenon in terms of preservation of the protein product.

• Answer:

  The genetic code is redundant - that is several codons per amino acid. A practical consequence of redundancy is that some errors in the genetic code only cause a silent mutation or an error that would not affect the protein because the hydrophilicity or hydrophobicity is maintained by equivalent substitution of amino acids; for example, a codon of NUN (where N = any nucleotide) tends to code for hydrophobic amino acids. NCN yields amino acid residues that are small in size and moderate in hydropathy; NAN encodes average size hydrophilic residues; UNN encodes residues that are not hydrophilic