Bi1X_Week7_GeneExpression_2011_v2

Bi1X_Week7_GeneExpression_2011_v2 - Gene Expression Daniel...

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Unformatted text preview: Gene Expression Daniel Jones May 9, 2011 1 Introduction What makes a human eye cell different from a skin cell? Both have the same set of genes. But clearly, they differ substantially in both structure and function. The reason, in part, is that although both cells share the same genes , they have different profiles of gene expression . The question of how gene expression is regulated is a major area of inquiry in contemporary biology, both because of its importance to biological function, and because of the richness and diversity of gene regulation strategies that can be found in nature. Gene regulation occurs at all steps along the central dogma, from methylation of genomic DNA, to post-translational modification of proteins. Today, we will focus on how gene expression is regulated at the level of transcription initiation, or “transcriptional regulation,” for short. Transcriptional regulation in prokaryotes is largely mediated by proteins that bind to DNA, called “transcription factors” (TFs). Most TFs bind specifically to a particular DNA sequence. For instance, the lac repressor protein binds strongly to the sequence AATTGTGAGCGCTCACAATT. TFs can be broadly categorized as either activators or repressors. Activators are proteins which ex- hibit favorable energetic interactions with RNA polymerase (RNAP). When an Figure 1: Schematic of the promoter architecture to be investigated in this experiment. It consists of a lacUV RNAP binding site, immediately followed by an LacI binding site (shown here as O2). The promoter is driving expression of YFP. 1 (a) Activation. An activator called CRP and RNA polymerase (RNAP) enjoy favorable en- ergetic interaction, represented by the binding energy ad . Δ ad : activator-DNA binding en- ergy. Δ pd : RNAP-DNA binding energy....
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Bi1X_Week7_GeneExpression_2011_v2 - Gene Expression Daniel...

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