Translation of an mRNA message into its polypeptide product on the ribosome is a polymerization reaction, and can be divided into three phases: initiation, elongation, and termination. Initiation requires the assembly of the translational machinery from its individual components to form a complex that is primed for peptide bond formation. Formation of this initiation complex […]

Process of protein biosynthesis

Tate, W. P., Poole, E. S. and Mannering, S. A. 2001. Protein Synthesis Termination. eLS. .

Fig. 8.16 Translation process of protein synthesis in prokaryotes.

Initiation of protein synthesis requires assembly of the ribosomal subunits, messenger RNA, and initiator tRNA at the start codon. This organization of translational components is facilitated by protein initiation factors (Fig. 5). FIGURE 5 Translation initiation. In prokaryotes, three initiation factors are responsible for assembling the initiation complex prior to decoding of a message. The […]

Components of Protein Synthesis

The heart of protein biosynthesis lies in the elongation cycle, with its sequential decoding of mRNA codons to assemble the useful portion of the polypeptide. Elongation can be further broken down into three phases— aminoacyl-tRNA decoding, peptide bond formation, and translocation of the new peptidyl-tRNA (Fig. 7). A. Decoding According to Base Pairing Comparison of […]

Initiation of protein synthesis; formation of the initiation complex.

Procedure of Protein Synthesis - Web Books

One of three mRNA codons - UAA, UAG and UGA - is used to signal to the elongating ribosome that translation should be terminated at this point. Upon the arrival of the stop codon at the ribosomal acceptor(A)-site, a protein release factor (RF) binds to the ribosome resulting in the peptidyl transferase centre of the ribosome switching to a hydrolytic function to remove the completed polypeptide chain from the peptidyl-tRNA bound at the adjacent ribosomal peptidyl(P)-site. In this review recent advances in our understanding of the mechanism of termination in the bacterium Escherichia coil will be summarised, paying particular attention to the roles of 16S ribosomal RNA and the release factors RF-1, RF-2 and RF-3 in stop codon recognition. Our understanding of the translation termination process in eukaryotes is much more rudimentary with the identity of the single eukaryotic release factor (eRF) still remaining elusive. Finally, several examples of how the termination mechanism can be subverted either to expand the genetic code (e.g. selenocysteine insertion at UGA codons) or to regulate the expression of mammalian retroviral or plant viral genomes will be discussed.

What are the basic steps of protein synthesis? | Chemistry

Following release of the synthesized protein, the ribo-some contains an empty tRNA in the P-site or E-site, and mRNA is still bound with the stop codon in the A-site. This arrangement of components is the post-termination complex. A protein known as the ribosome recycling factor (RRF) promotes the dissociation of this complex in preparation for […]

Termination of protein synthesis and release of the completed protein.

Animation of Protein Synthesis (Translation) in Prokaryotes.

Quality control and chaperones
If at all, a wrong amino acid is added, tRNA synthetase removes the incorrectly attached amino acid through hydrolytic editing. There are protein molecules called chaperones that catalyze the correct folding of other proteins within the cell. They also help in preventing aggregation. The hsp70 family of molecular chaperones helps in correct folding after synthesis.

Should be associated with the ribosomes, the site of protein synthesis.

Inhibition of Protein Synthesis by ..

i.ρ-dependent Termination: In some prokaryotes, the termination of transcription is helped by a ρ (rho) protein that gets attached at the 5′ end of the newly synthesizing mRNA. The ρ then moves along the mRNA and induces the formation of hairpin loop near the 3′ end of mRNA due to the presence of inverted repeated sequences. This helps in the detachment of mRNA from the DNA (Fig. 8.9).

The ribosomal subunits are reusable and not for the synthesis of a specific protein.


When the mRNA stop codon is reached, the fully synthesized protein does not simply fall off the ribosome. Release factors (RFs) are the protein assistants that recognize the presence of a stop codon in the ribosomal A-site and trigger cleavage of the polypeptide from the P-site tRNA (Fig. 9). In prokaryotes, RF1 hydrolyzes the protein […]