Ribosome and rRNA

The effect of unsaturated fatty acid depletion on mitochondrial ribosome and rRNA formation has been investigated. The guanine plus cytosine content of the RNA isolated from the mitochondrial preparations was about 32-37%, compared with 47% for cytoplasmic rRNA and 27% for pure mt rRNA. These data suggest that transcription products of mitochondrial DNA were present. However, no ribosomal subunits could... 

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. 

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

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). 

Griffiths RI, Whiteley AS, O Donnell AG, Bailey MJ. Rapid method for coextraction of DNA and RNA from natural environments for analysis of ribosomal DNA-and rRNA-based microbial community composition. Appl. Environ. Microbiol. 2000 66 5488-5491. 

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... 

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