Prokaryotic protein synthesis

The protein synthesis machinery reads the RNA template starting from the 5 end (the end made first) and makes proteins beginning with the amino terminus. These directionalities are set up so that in prokaryotes, protein synthesis can begin even before the RNA synthesis is complete. Simultaneous transcription-translation can t happen in eukaryotic cells because the nuclear membrane separates the ribosome from the nucleus. 

Protein synthesis inhibition—prokaryotes Protein synthesis inhibition—eukaryotes Mistranslation on ribosomes Nonsense mutation suppression DNA translation Phenotypic suppression Membrane leakiness Nucleic acid binding/precipitation... 

Infections by the ulcer-causing bacterium Helicobacter pylori can be treated effectively with a prolonged course of doxycycline or another of the tetracycline family of antibiotics, potent inhibitors of prokaryotic protein synthesis. 

Steps in prokaryotic protein synthesis (translation). (Continued on the next page)... 

Chloramphenicol acetyl transferase (CAT). This bacterial enzyme was the first reporter protein used for studying the transcriptional activity of eukaryotic regulatory sequences (Gorman et al., 1982). CAT inactivates chloramphenicol, an inhibitor of prokaryotic protein synthesis, by converting it to the mono- or di-acetylated species. Measurement of CAT activity requires a 14C-radiolabeled chloramphenicol or acetyl-CoA and, therefore, an additional step is neccessary to separate the radio-labeled reactant from the product. Novel detection methods based on fluorescent substrates or ELISA assays, which do not use radiolabeled reagents, have been described more recently (Bullock and Gorman, 2000). 

The broad outlines of eukaryotic protein synthesis are the same as in prokaryotic protein synthesis. The genetic code is generally the same (some microorganisms and eukaryotic mitochondria use slightly different codons), rRNA and protein sequences are recognizably similar, and the same set of amino acids is used in all organisms. However, specific differences exist between the two types of protein synthesis at all steps of the process. 

Figure 12.2 Initiation reactions and elongation cycle in prokaryotic protein synthesis.

S. Am., South American 70S PS, 70S ribosome (prokaryote) protein synthesis... 

There are also inhibitors that affect enzyme synthesis. Inhibitors of transcription (e.g., dibromothymoquinone [DBMIB]) and inhibitors of translation (e.g., cyclo-heximide [CHX]) are available but these are not specific to particular enzymes. In addition, because protein synthesis takes place within the chloroplast and mitochondrion in eukaryotes, prokaryotic protein synthesis inhibitors (e.g., chloramphenicol [CAP]) may be necessary to distinguish prokaryotic versus eukaryotic activity (e.g., Segovia and Berges, 2005). 

Eukaryotic Protein Synthesis Differs from Prokaryotic Protein Synthesis Primarily in Translation Initiation... 

The basic plan of protein synthesis in eukaryotes and archaea is similar to that in bacteria. The major structural and mechanistic themes recur in all domains of life. However, eukaryotic protein synthesis entails more protein components than does prokaryotic protein synthesis, and some steps are more intricate. Some noteworthy similarities and differences are as follows ... 

Which of the following is required for certain types of eukaryotic protein synthesis but not for prokaryotic protein synthesis ... 

For each of the following steps in prokaryotic protein synthesis (Questions [9.1] to [9.3]), indicate the most appropriate antibiotic (A-J) to inhibit the process. 

Prokaryotic Protein Synthesis Eukaryotic Protein Synthesis... 

Prokaryotic protein synthesis is a rapid process involving several protein factors. 

The proteins involved in the initiation of prokaryotic protein synthesis are IF-1 (binds to the A site of the 30S subunit, blocking it during initiation), IF-2 (binds to the 30S subunit and promotes the binding of the initiating tRNA to the initiation codon of mRNA), and IF-3 (prevents the 30S subunit from binding prematurely to the 50S subunit). 

The bacterial selectivity of antibiotics pertains to an interference with prokaryotic protein synthesis as distinguished from eukaryotic protein synthesis (Muench, in Devlin, 1986, pp. 936,937). As has been indicated, however, some of the antibiotics are too toxic for clinical use, although useful in studying protein synthesis. 

Chloramphenicol Growth Blocks prokaryotic protein synthesis... 

Reflect and i ply In prokaryotic protein synthesis, formylmethio-nine (fmet) is the first amino acid incorporated, whereas (normal) methionine is incorporated in eukaryotes. The same codon (AUG) serves both. What prevents methionine from being inserted into the beginning and formylmethionine in the interior ... 

Reflect and Apply What is the energy cost per amino acid in prokaryotic protein synthesis Relate this to low entropy. 

Despite evident similarities in mRNA translation, the molecular mechanisms underlying ribosomal recruitment and start site selection differ substantially between bacteria and eukaryotes. In most prokaryotes protein synthesis and mRNA synthesis occur simultaneously, whereas eukaryotes have decoupled gene expression by localizing transcription... 

Add IPTG to E. coli cells growing in a medium containing a carbon source other than lactose in both the presence and the absence of an inhibitor of prokaryotic protein synthesis, like chloramphenicol. If zymogen activation is involved, chloramphenicol will not inhibit induction. If the synthesis of new protein is involved (as it is), induction will not be observed in the presence of chloramphenicol. 

RS. Patel et al., Badllaene, a novel inhibitor of prokaryotic protein-synthesis produced by Bacillus subtilis - Production, taxonomy, isolation, physicochemical characterisation and biological activity. J. Antibiot. 48, 997-1003 (1995)... 

Drew, D.D. A mathematical model for prokaryotic protein synthesis. Bull. Math. Biol. 63, 329-351 (2001)... 

In addition to the different translational factors and mechanisms used by eukaryotic organisms as described earlier, an organizational difference exists in eukaryotes that contrasts with prokaryotic protein synthesis. In organisms lacking a nucleus, transcription of the genetic message from DNA to RNA occurs in the same location as translation. In fact, bacterial ribosomes typically be-... 

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