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Lecture 7

BIOSC 0160 Lecture 7: Biology 2 Lecture 1.7: Bacterial Gene Regulation Part 2

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University of Pittsburgh
Biological Sciences
BIOSC 0160

Biology Week 5 13117 Lecture 1.7 How are bacterial genes regulated? Positive control of transcription and global gene regulation and intro to eukaryotic gene regulation lacZ and lacY are under negative control; lacI protein represses them by binding to the operator o Lactose = inducer allosterically binds to the repressor so that it cant inhibit expression o lacY permease o lacZ bgalactosidase In positive control, gene transcription is turned on by an activator (regulatory protein) o Arabinose: sugar found in cell walls o Ara operon: operon of E coli contains 3 genes which code for enzymes that metabolize arabinose o AraC regulatory protein is on the opposite strand of the operon Can both positively and negatively regulate Regulated by arabinose, which acts as an activator for ara operon Form a dimer and bind within the initiator with RNA polymerase Can negatively inhibit its own transcription Regulons: a set of different genes or operons that have separate promoters, but are controlled by the same regulatory proteins that bind to identical sequences SOS response regulon: is under negative control. o Repressor lexA is bound to an operator which represses 40 genesoperons involved in DNA repair o In response to DNA damage, RecA becomes activated and causes lexA to selfcleave ToxR regulon: produces cholera toxin o Inactive when bacteria live in water, but in the human gut an activator protein activates and binds to ToxR regulon resulting in gene transcription and toxin production o Toxin binds to epithelial cells, enters through endocytosis and signals activate ion efflux channels (anions leave the cell and we lose water, results in the symptoms) Differential gene expression: results in different cell types in functions in multicellular eukaryotes regulate gene expression in response to both external and internal environments Eukaryotes have three types of gene regulation that can occur in the nucleus: o Chromatin remodeling DNA is complexes with protein it must be opened for transcription to occur Chromatin is tightly packed but has an ordered structure DNA Is wrapped around histone proteins forming nucleosomes (beads) linked together by DNA (string) Nucleosome: composed of 4 kinds of core histone proteins 2 H2AH2B dimers and an H3H4 tetramer, DNA wraps around (147 base pairs twice) Linker histone H1: seals DNA to core histones DNA linker: connects nucleosomes (80 base pairs) 30nm fiber: tightly packed unit of nucleosomes o Transcriptional control
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