Protein synthesis stages

Genes are DNA and carry the inheritable characteristics of an organism and these characteristics are normally expressed at the molecular level via protein synthesis Gene expression consists of two stages transcription and translation, both of which involve RNAs Sections 28 11 and 28 12 describe these RNAs and their roles m transcription and translation... 

The oxazolidinones have a novel mechanism of action that involves the inhibition of bacterial protein synthesis at the very early stage, prior to chain initiation [55-58]. They are effective against a broad range of Gram-... 

IFl-3). In contrast, eukaryotic initiation is a rather complex process involving a large number of initiation factors (elFs, Table 1). This is also the stage of eukaryotic ribosomal protein synthesis, which is most highly regulated to achieve differential protein expression. Elaborating the details of eukaryotic initiation is beyond the scope of this chapter. 

At this stage, it is clear that ribosomal protein synthesis will not allow the incorporation of D-amino acids or those that are too bulky, and that only a-ami-no and a-hydroxy acids can be introduced those with extended backbones such as y-amino acids cannot be introduced in this manner. Also, in spite of the development of improved suppressor tRNAs, the incorporation of small, highly polar amino acids remains difficult. 

In protein synthesis, there are three classes of RNA to worry about ribosomal RNA, rRNA messenger RNA, mRNA and transfer RNA, tRNA. All three classes of RNA play key roles in the final stage of the process the biosynthesis of proteins. However, we are going to take this one step at a time. We turn attention first to the... 

The first stage in protein synthesis is initiation, in which an aminoacyl-tRNA is positioned on one of the subunits of the ribosome. The attached amino acid will be the N-terminus of the completed protein. 

Bioconjugate Synthesis—Stage 1. As described above, we have already demonstrated our ability to produce thermoresponsive copolymer hydrogel particles that possess groups for protein attachment. 

As is well known, the first stage in synthesizing proteins is transcription of genetic code from DNA to messenger RNA (mRNA), a process that depends on RNA polymerase (transcriptase). A strand of nucleotides in RNA mirrors the order of nucleotides in DNA, thus containing information in a certain sequence in which amino acids must be bound to form the corresponding protein. Protein synthesis takes place on ribosomes, which can be represented as certain machines in which proteins and various amino acids are assembled. 

Beside this dermatoxic activity pederin (147) has various biological activities (92). When administered in appropriate doses to partially hepatectomized rats, this compound stimulates development of hepatic tissues. The inhibitory effect at the cellular level has been found in chicken heart fibroblast cultures, and mice embryo, dog kidney, HeLa, and KB cell lines. In plants, root growth of Lupinus albus is inhibited and mitosis in Allium cepa blocked at the metaphasic stage. Also, pederin (147) inhibits protein synthesis and growth of yeast cells. In addition, the treatment of rat ascites sarcoma with purified extracts of P. fuscipes produces almost complete regression. 

The ribosome can carry two aminoacyl-tRNAs simultaneously. In the chain elongation stage, the growing polypeptide is carried on one of these tRNAs. The chain is transferred to the second tRNA, which adds its amino acid to the growing peptide, and displaces the first tRNA. The ribosome then moves one codon along the mRNA to allow the next to be read. Termination of protein synthesis involves the release of the completed polypeptide, expulsion of the last tRNA, and dissociation of the ribosome from the mRNA. This is signaled by specific termination codons (UAA, UAG, or UGA) in the mRNA and requires the participation of various release factors. 

FIGURE 6.1 The different stages of protein synthesis. Transcription and processing of RNA messages occur within the nucleus. The mRNA is then transported into the cytoplasm for translation and post-translational modifications. 

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