The Standard Genetic Code can Evolve from a Two-Letter GC Code Without Information Loss or Costly Reassignments

Area of Science:

• Origin of Life
• Molecular Evolution
• Genetics

Background:

• The standard genetic code likely evolved from a simpler precursor encoding fewer amino acids.
• Understanding the expansion process is challenging due to the high cost of most genetic code changes.

Purpose of the Study:

• To propose a novel hypothesis for the expansion of the genetic code from a simpler form to the standard code.
• To explain the transition using a stepwise addition of nucleotide bases, inspired by recent synthetic codes.

Main Methods:

• Analyzing the prebiotic abundance of early amino acids.
• Examining the balance of amino acid hydrophobicity.
• Investigating GC content in genomic coding regions.
• Proposing a model for stepwise codon expansion starting with G and C.

Main Results:

• Evidence suggests the initial genetic code used guanine (G) and cytosine (C).
• The code likely expanded by introducing adenine (A) and uracil (U).
• Expansion may have proceeded by adding bases to the third, then second, and finally first positions of codons.

Conclusions:

• The proposed model posits a gradual expansion of the genetic code by creating new codons with additional letters.
• This mechanism circumvents the issue of costly code alterations during evolutionary transitions.
• The hypothesis is consistent with available empirical data on early amino acid assignments and genomic composition.