Steps in Protein Synthesis:
STEP 1: The first step in protein synthesis is the
transcription of mRNA from a DNA gene in the nucleus. At some
other prior time, the various other types of RNA have been synthesized
using the appropriate DNA. The RNAs migrate from the nucleus
into the cytoplasm.
Prior to the beginning of the protein synthesis, all of the
component parts are assembled in the ribosome which is the brown/tan
structure in the left graphic.
30S Subunit Ribosome - graphic
30S Subunit Ribosome - Chime
in new window
for an overall diagram.
STEP 2: Initiation:
In the cytoplasm, protein synthesis is actually initiated
by the AUG codon on mRNA. The AUG codon signals both the interaction
of the ribosome with m-RNA and also the tRNA with the anticodons
(UAC). The tRNA which initiates the protein synthesis has N-formyl-methionine
attached. The formyl group is really formic acid converted to
an amide using the -NH2 group on methionine (left
The next step is for a second tRNA to approach the mRNA (codon
- CCG). This is the code for proline. The anticodon of the proline
tRNA which reads this is GGC. The final process is to start growing
peptide chain by having amine of proline to bond to the carboxyl
acid group of methinone (met) in order to elongate the peptide.
|Quiz: The next codon is UAU.
What is the next amino acid to be added?
The other graphic on the left shows this process at the molecular