Eukaryotic cells protein synthesis

Translation is the whole process by which the nucleotide sequence of an mRNA is used to order and to join the amino acids in a polypeptide chain (see Figure 4-1, step0). In eukaryotic cells, protein synthesis occurs in the cytoplasm, where three types of RNA molecules come together to perform different but cooperative functions (Figure 4-19) ... 

DNA is found primarily in the nucleus of eukaryotic cells. Protein synthesis takes place primarily in that part of the cell called the cytoplasm. Protein synthesis requires that two major processes take place the first occurs in the cell nucleus, the second in the cytoplasm. The first is transcription, a process in which the genetic message is transcribed onto a form of RNA called messenger RNA (mRNA). The second process involves two other forms of RNA, called ribosomal RNA (rRNA) and transfer RNA (tRNA). 

Chloramphenicol an antibiotic, M, 323, from Streptomyces venezuelae. There are 4 stereoisomers, of which only D(-)-threo-C. (Fig.) is an antibiotic. C. inhibits protein synthesis on 70S ribosomes of prokaryotes, and on the mitochondrial ribosomes of eukaryotic cells. Protein synthesis on SOS eukaryotic ribosomes is not affected. C. inhibits peptide bond formation and peptidyl transferase activity on the 50S ribo-somal subunit, by specifically binding to one of the SOS ribosomal proteins involved in these reactions. The protein in question is probably localized in the acceptor-donor region of the ribosome. C. is used as a broad-spectrum antibiotic in the treatment, e.g. of typhoid fever, paratyphus, spotted fever, infectious hepatitis, dysentery, phtheiia and viral influenza . Because it inhibits protein synthesis in mitochondrial ribosomes, C. is relatively toxic. It is now produced entirely synthetically. 

A major goal in recombinant DNA technology is the production of useful foreign proteins by bacteria, yeast, or other cultured cells. Protein synthesis depends upon both transcription and translation of the cloned genes and may also involve secretion of proteins from the host cells. The first step, transcription, is controlled to a major extent by the structures of promoters and other control elements in the DNA (Chapter 28). Since eukaryotic promoters often function poorly in bacteria, it is customary to put the cloned gene under the control of a strong bacterial or viral X promoter. The latter include the X promoter PL (Fig. 28-8) and the lac (Fig. 28-2) and trp promoters of E. coli. These are all available in cloning vehicles. 

The efficiency of protein synthesis is Increased by the simultaneous translation of a single mRNA by multiple ribosomes. In eukaryotic cells, protein-mediated Interactions... 

Inhibition of HeLa cell protein synthesis following poliovirus infection correlates with the proteolysis of a 220,000 dalton polypeptide associated with eukaryotic initiation factor 3 and a cap binding protein complex, J. Biol. Chem. 257 14806. 

Ribosomes are ancient ribonucleoprotein complexes that are the sites of protein synthesis in living cells. Their core structures and fundamental functional mechanisms have been conserved throughout the three domains of life bacteria, archaea and eukaryotes. All ribosomes are organized into two subunits that are defined by their apparent sedimentation coefficient, measured in Svedberg units (S). There is a general... 

In all eukaryotic cells there are small nuclear RNA (snRNA) species that are not directly involved in protein synthesis but play pivotal roles in RNA processing. These relatively small molecules vary in size from 90 to about 300 nucleotides (Table 35-1). 

All eukaryotic cells have four major classes of RNA ri-bosomal RNA (rRNA), messenger RNA (mRNA), transfer RNA (tRNA), and small nuclear RNA (snRNA). The first three are involved in protein synthesis, and snRNA is involved in mRNA splicing. As shown in Table 37-1, these various classes of RNA are different in their diversity, stability, and abundance in cells. 

Other antibiotics inhibit protein synthesis on all ribosomes (puromycin) or only on those of eukaryotic cells (cycloheximide). Puromycin (Figure 38—11) is a structural analog of tyrosinyl-tRNA. Puromycin is incorporated via the A site on the ribosome into the carboxyl terminal position of a peptide but causes the premature release of the polypeptide. Puromycin, as a tyrosinyl-tRNA analog, effectively inhibits protein synthesis in both prokaryotes and eukaryotes. Cycloheximide inhibits peptidyltransferase in the 60S ribosomal subunit in eukaryotes, presumably by binding to an rRNA component. 

The catalytic activities of the fortified wheat germ cell-free systems supplemented with each fraction were investigated (Fig. 2). As shown in Fig. 2, only 0 - 40 % ammonium sulfate fraction showed an enhancement in DHFR protein synthesis. This enhancement of protein experimental results and the fact that the various eukaryotic initiation factors are contained in synthesis was also confirmed by SDS-PAGE and autoradiography (Fig. 3). From the above 0-40 % ammonium sulfate fraction [5, 6], it can be concluded that the amount of initiation factors in a conventionally prepared wheat germ cell-fi extract is deficient for the translation of DHFR with internal ribosome entry site. Therefore, it needs to supplement a wheat germ cell-free extract with the fraction containing the limited initiation factors for the efficient protein translation, and this fortified cell-free system can be easily made by simple... 

Abstract. In eukaryotic cells, replicated DNA molecules remain physically connected from their synthesis in S phase until they are separated during anaphase. This phenomenon, called sister chromatid cohesion, is essential for the temporal separation of DNA replication and mitosis and for the equal separation of the duplicated genome. Recent work has identified a number of chromosomal proteins required for cohesion. In this review we discuss how these proteins may connect sister chromatids and how they are removed from chromosomes to allow sister chromatid separation at the onset of anaphase. 

Nicchitta, C. V., Lerner, R. S., Stephens, S. B., Dodd, R. D., and Pyhtila, B. (2005). Pathways for compartmentalizing protein synthesis in eukaryotic cells The templatepartitioning model. Biochem. Cell Biol. 83, 687—695. 

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. 

The answer is b. (Hardman, p 1131.) Chloramphenicol inhibits protein synthesis in bacteria and, to a lesser extent, in eukaryotic cells. The drug binds reversibly to the. 505 ribosomal subunit and prevents attachment of aminoacybtransfer RNA (tRNA) to its binding site. The amino acid substrate is unavailable for peptidyl transferase and peptide bond formation. 

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