The process by which mRNA is decoded to produce a protein is called translation. The translation of mRNA into protein starts with the assembly of a complex on the mRNA strand. Initially, three initiation factor proteins (IF1, IF2, and IF3) attach to the small subunit of the ribosome. This, combined with a methionine-carrying tRNA, binds to the mRNA near the AUG start codon to form the initiation complex. After the initiation complex has assembled on the mRNA, the large ribosomal subunit attaches to this complex. Each group of three bases on the mRNA (a codon) codes for a specific amino acid, and this sequence guides the assembly of amino acids into a protein. During the elongation phase, the ribosome moves along the mRNA from the 5' end to the 3' end. This movement, known as translocation, requires the elongation factor G. The tRNA matching the second codon can then attach to the A site of the ribosome. This process needs elongation factors and GTP for energy. The ribosome then forms peptide bonds between adjacent amino acids through a peptidyl transferase activity, linking them into a growing polypeptide chain. This process continues until the ribosome has read all the codons on the mRNA and assembled the amino acids in the correct sequence. Lastly, translation ends when the ribosome encounters one of the three termination codons (UAA, UGA or UAG). These codons do not have corresponding tRNAs. Instead, proteins called release factors bind to these codons, causing the ribosome to release the newly made protein and detach from the mRNA.