Tuesday, July 27, 2010

RNA Metabolism

The RNA (Ribonucleic acid) of the cell is partly in the nucleus, partly in particles in the cytoplasm and partly as the "soluble" RNA of the cell sap; many workers have shown that all these three fractions turn over differently. It is very important to realize in any discussion of the role of RNA in the cell that it is very in homogeneous metabolically, and probably of more than on type. –Francis H.C. Crick, article in Symposia of the society for Experimental Biology. 1958.

Expression of the information in a gene generally involves production of an RNA molecule transcribed from a DNA template. Strands of RNA and DNA may seem quite similar at first glance, differing only in that RNA has hydroxyl group at the 2' position of the aldopentose, and uracil instead of thymine. However, unlike DNA, most RNA carry out their functions as single strands, strands that fold back on themselves and have the potential for much greater structural diversity than DNA. RNA is thus suited to variety of cellular functions.All RNA molecules except the RNA genomes of certain viruses are derived from information permanently stored in DNA. During transcription, and enzyme system converts the genetic information in a segment of double-stranded DNA into and RNA strand with a base sequence complementary to one of the DNA strands. Three major kinds of RNA are produced. Messenger RNAs (mRNAs) encode the amino acid sequence of one or more polypeptides specified by a gene or set of genes. Transfer RNAs (tRNAs) read the information encoded in the mRNA and transfer the appropriate amino acid to a growing polypeptide chain during protein synthesis. Ribosomal RNAs (rRNAs) are constituents of ribosome, the intricate cellular machines that synthesize proteins. Many additional specialized RNAs have regulatory or catalytic functions or are precursors to the three main classes of RNA.

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