Ribosomal RNA rRNA

Ribosomes contain several different RNA molecules, three in prokaryotic ribosomes and four in eukaryotic ribosomes. For historical reasons, each class is characterized by its sedimentation coefficient, which represents a typical size. For prokaryotes, the three Escherichia coli rRNA molecules are used as size standards they have sedimentation coefficients of 5S, 16S, and 23S. The E. coli rRNA molecules have been sequenced and contain 120, 1541, and 2904 nucleotides, respectively. The sizes of the prokaryotic rRNA molecules vary very little from one species of bacterium to another. 

Eukaryotic rRNA molecules are generally larger and there are four eukaryotic rRNA molecules. Rat liver rRNA molecules are used as standards the S values and the average number of nucleotides are 5S (120), 5.8S (150), 18S (2100), and 28S (5050), respectively. The eukaryotic 5.8S species corresponds functionally to the prokaryotic 

5S species no prokaryotic rRNA molecule corresponds to the eukaryotic 5S rRNA. 

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

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). 

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. 

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-... 

Several different types of RNA, including ribosomal RNA (rRNA), transfer RNA (tRNA), and messenger RNA (mRNA), are involved in protein synthesis. 

All four scientists whose work led to modification of the dogmas received the Nobel Prize. Thomas Cech (1987) was the first to observe enzyme-like reactions taking place at the same RNA strand, in ribosomal RNA (rRNA) from the proto-zoon Tetrahymena thermophila. The RNA produced, which is completely viable, is formed in a process in which certain sections (introns) of the primary copy (the transcription of DNA to mRNA) are cut out, the two remaining ends of the exon then being rejoined (spliced). 

Nucleic acids can contain of any one of three kinds of pyrimidine ring systems (uracil, cytosine, or thymine) or two types of purine derivatives (adenine or guanine). Adenine, guanine, thymine, and cytosine are the four main base constituents found in DNA. In RNA molecules, three of these four bases are present, but with thymine replaced by uracil to make up the fourth. Some additional minor derivatives are found in messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), particularly the N4,N4-dimethyladenine and N7-methylguanine varieties. 

The RNA molecules, ribosomal RNA (rRNA) and messenger RNA (mRNA) play key roles in the protein synthesis. The amount of RNA in individual cells or in a community may, therefore, be taken as an indicator of protein synthesis and, thus, microbial activity. The number of active cells can be detected by fluorescent in situ hybridization (FISH) (Amann et al. 1995). By this method, individual cells carrying high concentrations of rRNA, situated on ribosomes, are quantified by fluorescence microscopy. The amount of rRNA in a community can also be detected by Reverse Transcriptase Polymerase Chain Reaction (RT-PCR), where rRNA extracted from soil is detected by creating a DNA copy and separating by gel electrophoresis (Duineveld et al. 2001). 

The next process is similar in both eukaryotes and prokaryotes, and involves the translation of mRNA molecules into polypeptides. This procedure involves many enzymes and two further types of RNA transfer RNA (tRNA) and ribosomal RNA (rRNA). There is a specific tRNA for each of the amino acids. These molecules are involved in the transportation and coupling of amino acids into the resulting... 

Whereas DNA is mostly located in the nucleus of cells in higher organisms (with some also in mitochondria and in plant chloroplasts), RNA comes in three major and distinct forms, each of which plays a crucial role in protein biosynthesis in the cytoplasm. These are, respectively, ribosomal RNA (rRNA), which represents two-thirds of the mass of the ribosome, messenger RNA (mRNA), which encodes the information for the sequence of proteins, and transfer RNAs (tRNAs) which serve as adaptor molecules, allowing the 4-letter code of nucleic acids to be translated into the 20-letter code of proteins. These latter molecules contain a substantial number of modified bases, which are introduced enzymatically. 

Mitochondrial DNA contains 37 genes, all of which are essential for normal mitochondrial function. Thirteen of these genes provide instructions for making enzymes involved in oxidative phosphorylation. The remaining genes provide instructions for making molecules called transfer RNAs (tRNAs) and ribosomal RNAs (rRNAs), which are chemical cousins of... 

Ribosomal RNA (rRNA), vtrhich is the most abundant type of RNA in the cell. It is used as a structural component of the ribosome. Ribosomal RNA associates with ribosomal proteins to form the complete, functional ribosome. 

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 origin of the idea that a ribosome might be a ribozyme is derived from the experiment in which peptidyl transferase activity was observed even after digestion of protein components of the ribosome [15]. This was surprising because the most important biological function involved in the synthesis of proteins is catalyzed by RNA. Recently, a large ribosomal subunit from Haloarcula marismortui was determined at a resolution of 2.4 A [16, 155]. Importantly, because of the absence of proteins at the active site, it was concluded that the key peptidyl transferase reaction is accomplished by the ribosomal RNA (rRNA) itself, not by proteins. How does it work ... 

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