a Universal Genetic Code

the genetic code used by all known forms of life & is nearly universal with few minor variations, thus a single evolutionary history (LUCA) may underlie the origin of the genetic code.     - the genetic code clusters certain amino acid, i.e.,             amino acids with similar physical properties tend to have similar mid-letter codons     - amino acids that share the same biosynthetic pathway tend to have the             same first base in their codons What about synonymous codon? [GUU, GUC, GUA,GUG] do they make the same proteins??? Subramaniam et al (2013, PNAS) using an E.coli protein synthetic systems and artificial mRNAs with synonymous codons found that they all made equivalent proteins, but under stress conditions, as where a reduction in amino acid supply was present, a 100 fold difference in protein synthetic rates between synonymous gene variants was observed...       Thus synonymony may be a strategy for genetic systems to expand their repertoire of responses to environment pertubations.