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The significance of rna molecules in microbiology, their various types, functions, and the process of protein synthesis through translation. It discusses the evolution of rna and its role in genetic information storage and enzymatic activity.
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Harriet Wilson, Lecture Notes Bio. Sci. 4 - Microbiology Sierra College
Considerable evidence suggests that RNA molecules evolved prior to DNA molecules and proteins, and that many processes now involving DNA and proteins were previously accomplished by RNA alone. Many RNA molecules have enzymatic activity, and like DNA contain genetic information stored as nucleotide sequences. In living cells encountered today, RNA molecules are formed from DNA templates through transcription, but this was not always so. It is no wonder then that RNA molecules play such important roles within living cells. Types of RNA molecules: Although cellular RNA molecules are typically made via transcription using DNA as a template, they are coded for by different genes and have a variety of different functions. RNA molecules typically found in both prokaryotic and eukaryotic cells include:
Translation can be broken into a series of stages as follows:
3) Termination Translation is terminated when the ribosome reaches a stop or terminator codon. In both prokaryotic and eukaryotic cells, the process involves the interaction of two or more proteins called chain release factors. When a stop codon is recognized, the finished polypeptide chain is released from the last t-RNA, i.e., the covalent bond attaching the last amino acid added to its corresponding t-RNA molecule is hydrolyzed. Following this reaction, the t-RNA is released from the ribosome, and the two ribosomal subunits separate, releasing the m-RNA. Since messenger-RNA molecules have a relatively short life expectancy (about 2 minutes in some eukaryotic cells), bacteria often increase translation efficiency by binding multiple ribosomes to the same m-RNA during translation. A group of ribosomes bound to and translating the same m-RNA is called a polyribosome or polysome. 0 In eukaryotic cells, m-RNA molecules typically carry the information copied from individual genes (transcription is monocistronic ), but in prokaryotic cells, m-RNA molecules often carry the information copied from multiple genes (transcription is polycistronic ). Polycistronic m-RNA molecules carry information that is translated into multiple polypeptides. In E.coli the m-RNA copied from the tryptophan biosynthesis operon contains about 7000bp and is translated into five different enzymes. Each protein is coded for by a section of m-RNA having its own start and stop signals, i.e., initiation and termination sequences. For a fun and simple review of the translation process take a look at this site. http://www.phschool.com/science/biology_place/biocoach/translation/term.html