Protein Synthesis (Translation)
From mRNA to a chain of amino acids
Summary
The ribosome reads mRNA in groups of 3 bases (codons) and turns each one into an amino acid. tRNA matches the mRNA with its anticodon and brings the corresponding amino acid. The amino acids are joined by peptide bonds and become a protein.
In depth
Translation is one of the most complex molecular processes in the cell, a kind of 3D assembly line. mRNA is made in the nucleus and moves out into the cytoplasm; the ribosome (a huge complex that is part RNA, part protein) attaches near the 5' end of the mRNA and finds the AUG start codon. Each codon (3 bases) codes for a particular amino acid or a "stop" signal; this genetic code is almost universal, the same from bacteria to humans. tRNA molecules carry amino acids; the 3 bases at one end (the anticodon) pair with an mRNA codon. The matching tRNA enters the ribosome's A site; a peptide bond forms with the previous amino acid and the ribosome moves on by one codon. Synthesis ends at a stop codon (UAA, UAG, UGA): the protein is released and begins to fold. In human cells a few amino acids are added per second, so a medium-sized protein is finished in a minute or two. Without this machine, there would be no life.
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