Prokaryotes and eukaryotes

MacKinnon, R., et al. Structural conservation in prokaryotic and eukaryotic potassium channels. Science 280 106-109, 1998. 

Without consulting chapter figures, sketch the characteristic prokaryotic and eukaryotic cell types and label their pertinent organelle and membrane systems. 

FIGURE 11.25 The organization and composition of prokaryotic and eukaryotic ribosomes. 

Both prokaryotes and eukaryotes are capable of introducing a single cis double bond in a newly synthesized fatty acid. Bacteria such as E. coli carry out this process in an Og-independent pathway, whereas eukaryotes have adopted an Og-dependent pathway. There is a fundamental chemical difference between the two. The Og-dependent reaction can occur anywhere in the fatty acid chain. 

Still more confusion plagued early researches, when it was not realized that the biosynthetic routes to thiamine in prokaryotes and eukaryotes are quite different, a fact not expected at the outset. Thus, evidence collected from the study of yeast could not be transposed to bacteria, and vice-versa. For instance, formate is a most efficient precursor of one of the carbon atoms of the pyrimidine part of thiamine (pyramine), both in yeasts and enterobacteria, but incorporates at C-2 in bacteria and at C-4 in yeast. However, as is briefly covered in Section VIII, this dichotomy of pathways might have a deep significance in the perspective of biochemical evolution during primitive life on Earth. 

The D-fructose 1,6-bisphosphate aldolase (FruA EC 4.1.2.13) catalyzes in vivo the equilibrium addition of (25) to D-glyceraldehyde 3-phosphate (GA3P, (18)) to give D-fructose 1,6-bisphosphate (26) (Figure 10.14). The equilibrium constant for this reaction of 10 strongly favors synthesis [34]. The enzyme occurs ubiquitously and has been isolated from various prokaryotic and eukaryotic sources, both as class I and class II forms [30]. Typically, class I FruA enzymes are tetrameric, while the class II FruA are dimers. As a rule, the microbial class II aldolases are much more stable in solution (half-lives of several weeks to months) than their mammalian counterparts of class I (few days) [84-86]. 

Methyl parathion has been tested in numerous genotoxicity assays using prokaryotic and eukaryotic systems with both positive and negative results. Results of these studies are summarized in Tables 3-5 and 3-6. 

Formate dehydrogenases are a diverse group of enzymes found in both prokaryotes and eukaryotes, capable of converting formate to CO2. Formate dehydrogenases from anaerobic microorganisms are, in most cases, Mo- or W- containing iron-sulfur proteins and additionally flavin or hemes. Selenium cysteine is a Mo- ligand. 

In all prokaryotic and eukaryotic organisms, three main classes of RNA molecules exist messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA... 

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. 

Table 1.1 The main features distinguishing prokaryotic and eukaryotic cells... 

Despite the differences in nuclear structures between prokaryotes and eukaryotes, the genetic code, i.e. the combination of bases which does for a particular amino acid in the process of protein synthesis, is the same as it is in all living organisms. 

Mechanisms of active and passive transport in a family of homologous sugar transporters found in both prokaryotes and eukaryotes... 

In summary, studies on the human erythrocyte glucose transporter and other members of a large family of prokaryotic and eukaryotic sugar transporters have yielded... 

Despite the limited information available, rather clear predictions can be made about the probable structure, location, and energy coupling of the amino acid transporters of Saccharomyces cerevisiae, by comparing them with better known systems in both prokaryotes and eukaryotes. 

FIGURE 3.17 Cytochrome P450 systems in prokaryotes and eukaryotes. (From Neilson, A.H. and Allard, A.-S. Microbial metabolism of PAHs and heteroarenes, The Handbook of Environmental Chemistry, Vol. 3J, pp. 1-80, Springer, 1998. With permission.)... 

P450 systems (Sariaslani 1991), their widespread role in the transformation of xenobiotics (Smith and Davis 1968), and their occurrence and activities in yeasts (Kappeli 1986). The essential features of prokaryotic and eukaryotic cytochrome P450 systems are compared in Figure 3.17. 

These are produced by both prokaryotes and eukaryotes, and catalyze a number of important reactions. They are flavoproteins that produce potentially destructive H2O2 that is removed by the activity of catalase or peroxidase. The reactions are formally outlined in Figures 3.31a through c. 

The occurrence in some plants of secondary metabolites characterized by an 0-heterocyclic structure and exhibiting antimicrobial properties is a well-known phenomenon [2,8-10]. Among them, catechins and proanthocyanidins are two classes of compounds exhibiting antimicrobial properties towards both prokaryotic and eukaryotic microorganisms. Yet, despite the large number of studies published so far, the real potentialities and limitations given by the use of this class of molecules as antiviral or antimicrobial (antibacterial, antimycotic, antiprotozoal) agents have not been critically evaluated. The present chapter represents an overview of the re-... 

In spite of this redundancy of results, discrepancies among different data sets obtained from different laboratories on antimicrobial activity of these 0-heterocycles against both prokaryotic and eukaryotic microorganisms have been sometimes observed. This fact is probably due to various causes. 

Jackson, F. R. (1990). Prokaryotic and eukaryotic pyridoxal-dependent decarboxylases are homologous. J. Mol. Evol. 31 325-329. 

The dihydrofolate reductase enzyme (DHFR) is involved in one-carbon metabolism and is required for the survival of prokaryotic and eukaryotic cells. The enzyme catalyzes the reduction of dihydrofolate to tetrahydrofolate, which is required for the biosynthesis of serine, methionine, purines, and thymidylate. The mouse dihydrofolate reductase (mDHFR) is a small (21 kD), monomeric enzyme that is highly homologous to the E. coli enzyme (29% identify) (Pelletier et al., 1998). The three-dimensional structure of DHFR indicates that it is comprised of three structural fragments F[l], F[2] andF[3] (Gegg etal., 1997). 

Jebanathirajah, J. A. Andersen, S. Blagoev, B. Roepstorff, P. A rapid screening method to monitor expression of recombinant proteins from various prokaryotic and eukaryotic expression systems using matrix-assisted laser desorption ioniza-tion-time-of-flight mass spectrometry. Anal. Biochem. 2002, 305, 242-250. 

Eukaryotic chromosomes, unlike their bacterial counterparts, are linear rather than- circular. Since RNA oligonucleotides prime both prokaryotic and eukaryotic DNA synthesis, the 5 termini of the daughter... 

Kealey, J.T., Liu, L., Santi, D.V. et al. (1998) Production of a polyketide natural product in nonpolyketide-producing prokaryotic and eukaryotic hosts. Proceedings ofthe National Academy of Sciences ofthe United States of America, 95, 505—509. 

---