Chapter31Notes 11.45.23 PM

Chapter31Notes 11.45.23 PM - Page 1 of 16 Chapter 31 Notes...

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Unformatted text preview: Page 1 of 16 Chapter 31 Notes Biochemistry 461 F all 20 10 CHAPTER 31: CONTROL OF GENE EXPRESSION LECTURE TOPICS ! Differential Gene Expression in Procaryotes and Eucaryotes ! Regulation of Gene Expession ! Transcriptional Regulation by DNA-Binding Proteins ( E.coli Lactose Operon) ! Transcriptional and Postranscriptional Regulation (trp Operon Attenuation; ferritin/transferrin receptor in eucaryotes ) ! Helix-turn-helix motif of Procaryotic DNA Binding Proteins ! Eucaryotic Gene Regulation ! Complexity of Genomes ! Elaborate Mechanisms of Regulation ! Transcription Activation/Repression mediated by Protein-Protein Interactions OVERVIEW: PROCARYOTIC GENE EXPRESSION ! Once again - Bacteria ( E . coli ) are most well studied with regard to regulation of gene expression. Differences in rates of synthesis of some proteins varies over a 1000-fold range in response to changes in quantity and quality of metabolites, nutrients, environmental challenges, etc. ! Regulation of bacterial gene expression occurs most often at the level of transcription. Genes are often clustered in operons , all of whose genes are transcribed coordinately in a single mRNA molecule. These genes can be expressed at all times in the cell ( constitutive genes ) or they can be under the control of repressor and/or activator proteins ( inducible genes ). Page 2 of 16 ! Many regulatory proteins which bind to DNA have a helix-turn-helix-motif in common. ! Examples of operons whose transcriptional regulation is well known are the lactose and tryptophan operons of E . coli . ! Gene expression is also regulated at the translational level. [Exs.: trp operon in E. coli; ferritin and transferrin receptor in eucaryotes . OVERVIEW: EUCARYOTIC CHROMOSOMES AND GENE EXPRESSION ! Eucaryotic chromosomes are larger, have higher degrees of structural order, and a more complex composition than procaryotic chromosomes. The human genome (4x10 9 bp = 1 meter) is 1,000 times the size of that of E . coli . DNA (4x10 6 bp = 1.4 mm). Replication and gene expression is more complex than the procaryotic model. ! Eu caryotic chromosomal DNA is wound around histones in complexes called nucleosomes . The entire chromosome also contains many other proteins in a complex matrix called chromatin . ! A small fraction (1- 2%) of eucaryotic DNA is genes which code for proteins. There is an abundance of repetitive, non-coding sequences which comprise a significant fraction of eucarotic genomes. ! Eucaryotic gene expression is regulated primarily at the level of transcription . Transcriptionally active regions of chromosomes are extra- sensitive to DNase digestion and have reduced levels of cytosines which have been methylated. Expression of genes in these chromosomal regions is regulated by transcriptional factors. Page 3 of 16 ! Translational regulation occurs in iron metabolism genes....
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Chapter31Notes 11.45.23 PM - Page 1 of 16 Chapter 31 Notes...

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