Ribosomal RNAs

Ribosomal RNA (rRNA) is the major component of the ribosome, encompassing approximately two-thirds of the gross weight and forming the functional portion involved in protein synthesis. The other component of the ribosome consists of several proteins that are believed to assist in the maintenance of the required 3D structure of the active rRNA and which presumably have other functions as well. 

16S rRNA 23S rRNA,5S rRNA 18S rRNA 28S rRNA,5.8S rRNA,5S rRNA i i i i 

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Transfer or soluble RNAs are specific carrier molecules for amino-acids during protein synthesis on ribosomes with ribosomal RNA as the template. There is at least one t-RNA molecule for each amino-acid. 

The discovery of nbozymes (Section 28 11) in the late 1970s and early 1980s by Sidney Altman of Yale University and Thomas Cech of the University of Colorado placed the RNA World idea on a more solid footing Altman and Cech independently discovered that RNA can catalyze the formation and cleavage of phosphodiester bonds—exactly the kinds of bonds that unite individual ribonucleotides in RNA That plus the recent discovery that ribosomal RNA cat alyzes the addition of ammo acids to the growing peptide chain in protein biosynthesis takes care of the most serious deficiencies in the RNA World model by providing precedents for the catalysis of biologi cal processes by RNA... 

Resistance to Lincomycin. Resistance to lincomycin is developed slowly, and is usually caused by modification of 23S ribosomal RNA, which leads to co-resistance to macroHde, lincosaminide, and streptogramin B antibiotics (25). Inactivation of lincomycin by clinical isolates of strains of Staphjlococcus aureus and Staphjlococcus haemoljticus, though retention of sensitivity to macroHdes (see Antibiotics, macrolides) and streptogramins (see Antibiotics, peptides), has been found to be the consequence of the conversion of the antibiotic into its 3-(5 -adenylate) (26). 

Ribosomal RNA (rRNA) Ribosomes, which aie about two thirds nucleic acid and... 

In contrast, RNA occurs in multiple copies and various forms (Table 11.2). Cells contain up to eight times as much RNA as DNA. RNA has a number of important biological functions, and on this basis, RNA molecules are categorized into several major types messenger RNA, ribosomal RNA, and transfer RNA. Eukaryotic cells contain an additional type, small nuclear RNA (snRNA). With these basic definitions in mind, let s now briefly consider the chemical and structural nature of DNA and the various RNAs. Chapter 12 elaborates on methods to determine the primary structure of nucleic acids by sequencing methods and discusses the secondary and tertiary structures of DNA and RNA. Part rV, Information Transfer, includes a detailed treatment of the dynamic role of nucleic acids in the molecular biology of the cell. 

Ribosomes, the supramolecular assemblies where protein synthesis occurs, are about 65% RNA of the ribosomal RNA type. Ribosomal RNA (rRNA) molecules fold into characteristic secondary structures as a consequence of intramolecular hydrogen bond interactions (marginal figure). The different species of rRNA are generally referred to according to their sedimentation coefficients (see the Appendix to Chapter 5), which are a rough measure of their relative size (Table 11.2 and Figure 11.25). 

Ribosomal RNA has a complex secondary structure due to many intrastrand hydrogen bonds. 

Ribosomal RNAs characteristically contain a number of specially modified nucleotides, including pseudouridine residues, ribothymidylic acid, and methylated bases (Figure 11.26). The central role of ribosomes in the biosynthesis of proteins is treated in detail in Chapter 33. Here we briefly note the significant point that genetic information in the nucleotide sequence of an mRNA is translated into the amino acid sequence of a polypeptide chain by ribosomes. 

Ribosomes, the protein-synthesizing machinery of cells, are composed of two subunits, called small and large, and ribosomal RNAs are integral components of these subunits (see Table 11.2). A large degree of intrastrand sequence com-... 

The primary cellular function of mRNA is to direct biosynthesis of the thousands of diverse peptides and proteins required by an organism—perhaps 100,000 in a human. The mechanics of protein biosynthesis take place on ribosomes, small granular particles in the cytoplasm of a cell that consist of about 60% ribosomal RNA and 40% protein. 

Ribosomal RNA (Section 28.4) A kind of RNA used in the physical makeup of ribosomes. 

Linezolid (Zyvox) is the first of a new classification, an oxazolidinone, that acts by bindingto a site on a specific ribosomal RNA and preventing the formation of a component necessary for the bacteria to replicate It is... 

Mitochondria are unique organelles in man and higher animals in that they contain their own genome. Mitochondrial DNA (mtDNA) in humans is a small (16.5 kb), circular genome that encodes only 13 proteins, 22 transfer RNA (tRNA), and 2 ribosomal RNA (rRNA) molecules. mtDNA is inherited only from the mother and is present in multiple copies within one mitochondrion. 

Double-stranded DNA (calf thymus) Single-stranded DNA Heat-denatured DNA Closed circular DNA Ribosomal RNA (rat liver)... 

Not only eukaryotic cells but also bacteria have successfully been targeted by PNA anhsense strategies. Thus it has been shown that PNA complementary to ribosomal RNA or mRNA encoding an essential fatty acid biosynthesis protein, effectively kills E. coli. Furthermore, it has been shown that PNA directed to the start codon of the y -lactamase gene re-sensitized otherwise resistant E. coli to the antibiohc ampiciUin [64—66]. Conjugating a simple transporter peptide to the PNA increased the potency significantly, and an even more potent antibacterial PNA... 

Good L., Nielsen P.E. Inhibition of translation and bacterial growth by peptide nucleic acid targeted to ribosomal RNA. Proc. Natl Acad. Sci. USA 1998 95 2073-2076. 

Those cytoplasmic RNA molecules that serve as templates for protein synthesis (ie, that transfer genetic information from DNA to the protein-synthesizing machinery) are designated messenger RNAs, or mRNAs. Many other cytoplasmic RNA molecules (ribosomal RNAs rRNAs) have strucmral roles wherein they con-... 

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

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