Chemistry Reference
In-Depth Information
Figure 4.
Overview of protein translation.
The scheme for building the polypeptide
chain using the codons provided by
mRNA starts with the assembly of the
small and large ribosomal subunits at the
mRNA AUG initiation codon to form the
ribosomal complex. This assembly takes
place at the AUG initiation codon of the
mRNA, and requires the aminoacyl
tRNA-Met and proteins called initiation
factors to allow ribosomal assembly to
proceed. Next, with the help of elongation
factor proteins, the aminoacyl tRNA
which has an anticodon that matches the
next mRNA codon enters the “A” site of
the ribosome. The peptidyl transferase
enzyme will catalyze the formation of a
peptide bond between Met and the new
amino acid, leading to the release of the
tRNA that was originally linked to Met.
The new Met-AA-tRNA complex is
translocated to the “P” site, leaving the
“A” site vacant for the next incoming
tRNA-AA aminoacyl whose anticodon
matches the next mRNA codon. The
ribosomal complex proceeds in a 5ƍ to 3ƍ
direction along the mRNA, synthesizing
the nascent peptide chain from the N-
terminal to the C-terminal end, using the
repetitive process just described. The
arrival of the ribosome at the stop codon,
combined with the action of releasing
factor proteins, leads to the disassembly
of the ribosomal complex, the last tRNA,
and the release of the polypeptide chain.
