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Unformatted text preview: 17-1Cell and Molecular Biology (Biol. Chem. 410A)Lecture #17Harry R. Matthews, Ph.D.October 18, 1996RNA Structure and SynthesisClinical correlations:antibioticstuberculosisLearning objectives:flow of genetic informationgene expression1o, 2o, 3o structurecatalytic RNAclasses of RNARNA polymeraseOptional reading:Stryer IV Chapter 4, 5.Information Flow Pathway.The fundamental intracellular pathway for genetic information is shown in Figure 17-1. Gene expression involves the transcription of a gene encoded on the DNA into RNA and the translation of the RNA into protein. Replication involves the synthesis of two DNA molecules from one original.There are several subsidiary pathways that are important in specific situations.In DNA repair, the information on one strand of a DNA molecule is used to recreate the complementary strand. In some cases, the information on one chromosome is used to re-pair its matching chromosome. Transposition and gene rearrangements also provide mech-anisms for information flow within a set of chromosomes.Some viruses with DNA genomes can in-tegrate their DNA into the host chromosome. Other viruses, with RNA genomes, can copy the RNA sequence into DNA using the en-zyme, reverse transcriptase. Viruses can be formed using genetic material synthesized from the host DNA. A small group of viruses can replicate their RNA directly.Including these options gives the more com-plex pathway shown in Figure 17-2.In the more complete pathway, information can flow in both directions between DNA and RNA but only from RNA to protein, not from protein to RNA. The central role of RNA in this scheme is consistent with the idea that RNA was the basis of the first self-replicating systems, followed by the evolution of proteins and DNA.Gene Expression.The process of RNA synthesis by RNA poly-merase (transcription) will be outlined below. Gene activity is determined by several mech-Fundamental Fl owof Geneti c Inf ormat i onDNADNARNAprot ei nFigure 17-1. Fundamental Pathway.RNADNA DNARNA RNAproteinactive gene productreverse transcriptaseFigure 17-2. Complete Information Flow Pathway.17-2anisms which will be discussed in more detail in forthcoming lectures.RNA is made initially as a continuous com-plementary copy of one strand of the DNA. It is then modified, or processed, including spli-cing and capping, in the nucleus to produce a messenger RNA (mRNA) molecule. mRNA is transported to the cytoplasm. There, it com-bines with an RNA-protein complex called the ribosome which is the site of protein synthes-is. There is another layer of regulation that controls the initiation of protein synthesis on...
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- Spring '03