The genetic code

The genetic code is a fundamental concept in biology, encoding the instructions for life itself. It is the sequence of base triplets (codons) in mRNA which codes for specific amino acids.

• Triplet Code

  • The genetic code is a three-letter code, meaning that three bases (a triplet) code for one specific amino acid.

  • In DNA, these are called triplets.

  • In messenger RNA (mRNA), they are called codons.

  • In transfer RNA (tRNA), they are called anticodons.

• Universal

  • The genetic code is universal, meaning that the same specific base triplets/codons code for the same amino acids in almost all living things.

  • This universality suggests a common ancestor for all organisms and provides indirect evidence for evolution.

  • The shared biochemical basis allows for recombinant DNA technology, where DNA fragments from one organism can be transferred to another, and the transferred DNA can be translated in the recipient organism due to the universal nature of the code.

• Degenerate (or Redundant)

  • The genetic code is degenerate because there are more possible combinations of triplets (64) than there are amino acids (20).

  • This means that some amino acids are coded for by more than one base triplet.

  • The degenerate nature can limit the effect of mutations, as some substitutions may still code for the same amino acid, resulting in no change to the polypeptide.

• Non-overlapping

  • Each base triplet is read in sequence, separate from the triplet before and after it; base triplets do not share their bases.

  • This ensures the cell reads the DNA correctly and produces the correct sequence of amino acids.

• Start and Stop Signals

  • Not all triplets code for amino acids; some serve as "start signals" to initiate protein production (e.g., AUG for methionine), while others are "stop signals" (e.g., UAG, UAA, UGA) to terminate protein synthesis.

• Role in Protein Synthesis

  • The genetic code is the sequence of base triplets in DNA or mRNA that dictates the sequence of amino acids in a polypeptide.

  • DNA (deoxyribonucleic acid) stores this genetic information.

  • RNA (ribonucleic acid), specifically mRNA, transfers this information from DNA to the ribosomes.

  • The process involves transcription (copying DNA code into mRNA) and translation (using mRNA code to synthesize a polypeptide at ribosomes).

  • The order of bases in a gene determines the order of amino acids in a particular polypeptide, which in turn determines the protein's primary structure, shape, and function.