Genetic Code - Codons For Amino Acids

Genetic information which is transferred from parent to offspring is the basis of inheritance. The process begins with replication of DNA followed by transcription and translation. During transcription, genetic information stored in the DNA is copied into another form of RNA. The whole process is governed by the complementary base pairs of the two nucleic acids. However, the latter process of translation is not controlled by complementary but by the genetic code. Translation is the process of converting nucleic acid information into amino acids. Let’s learn more in detail about the genetic code.

Genetic Code

The genetic code comprises the complete information of the protein manufactured from RNA. It is the sequence of base pairs of amino acids that code for protein to be synthesized. Thus a change in this sequence can alter the formation of amino acids. Decoding the genetic code was a real challenge for scientists.

A physicist by name George Gamow suggested a solution to break this challenge.  He applied the concepts of permutation and combination to decipher this genetic code. He suggested that genetic code should be made of three nucleotides which code for 20 amino acids with four bases.

Genetic code- Codons for the Amino Acids

Four nitrogenous bases and three nucleotides together form a triplet codon which codes for one amino acid. Thus, the number of possible amino acids would be 4 x 4 x 4 = 64. But we have 20 naturally existing amino acids.

This was explained by the features of genetic code which are as follows:

Genetic Code

  • Some amino acids are coded by more than one codon thus making them to degenerate.
  • Each codon codes only for one specific amino acid.
  • The codes are universal irrespective of the type of organism, i.e. CGU would code for Arginine in animals as well as in bacteria but exceptions exist.
  • Out of 64 codons, 3 are stop codons which do not code for any amino acids and thus ends the process of translation.
  • AUG coding for Methionine is the only codon that acts an initiator codon.

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Practise This Question

Regarding the assertion and reason, select the correct choice.
Assertion [A]: The amino acid-bound tRNA enters the aminoacyl tRNA binding site.
Reason [R]: The amino acid-bound tRNA transfers the amino acid at the peptidyl tRNA site.