Codon (triplet code): In the mRNA open reading frame region, every three adjacent nucleotides are a group, encoding the start/stop information of an amino acid or peptide chain synthesis.

There are 64 codons in total, 61 encoding 21 amino acids, and 3 stop codons not encoding any amino acids. AUG not only represents methionine, but also represents the start codon if it is located at the translation start site of the mRNA

Characteristics of the genetic code

amino acid binding site

mRNA binding site

The amino acids involved in the formation of the peptide chain must be combined with the corresponding tRNA to form aminoacyl-tRNA, which is then transported to the ribosome.

Move along the 5’ end of the template mRNA strand to the 3’ end

A position (aminoacyl position): binds aminoacyl-tRNA

P position (peptidyl position): binds peptidyl-tRNA

E position (ejection position): releases t-RNA that has unloaded amino acids

ATP or GTP powered

Multiple enzymes, Mg2

protein factor

①Catalyze the decomposition of ATP into pyrophosphate and AMP

② AMP, enzyme, and amino acid are combined into an intermediate complex (aminoacyl-AMP-enzyme), in which the carboxyl group of the amino acid and the phosphate of adenosine phosphate are connected through an anhydride bond for activation

③ The activated amino acid combines with the free hydroxyl group at the 2' or 3' position of the ribose of the adenylate at the 3'-CCA end of the tRNA through an ester bond to form the corresponding aminoacyl-tRNA, and adenosine monophosphate (AMP) is released in a free form.

Prokaryotes: fMet-tRNAfMet

Eukaryotes: tRNAiMet

Materials: 30S small subunit, mRNA, fMet-tRNAfMet, 50S large subunit, three IFs, GTP and Mg2

start

extend

termination

start

extend