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Notes Chapter 29 Supplement (Lectures 13) - Biochem 2B03.docx
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Department
Biochemistry
Course
BIOCHEM 2B03
Professor
Margaret Fahnestock
Semester
Fall

Description
Biochem 2B03 Jasmyn Lee  The modern idea of the gene was developed from studies of bacterial metabolism Central Dogma of Molecular Biology  Jacob and Monod – originators of the modern idea of gene transcription o 1961 – postulate the existence of mRNA  base composition would reflect that of DNA  heterogenous in mass (reflecting myriad proteins found in cells)  able to associate with ribosomes – site of protein synthesis  High turnover rate – permitting regulated gene function Evidence for Regulation and the Existence of mRNA  Investigation of inducible systems in bacteria E. coli  Enzyme Induction: Bacteria make certain enzymes in variable rates responding to changes in environment  Synthesis of an enzyme that acts on compound A is induced by compound A o Compound A is called an inducer Constitutive and Inducible Systems  Constitutive Proteins o Synthesized at a constant rate (not regulated)  Eg/ “housekeeping proteins”: ribosomal proteins (10,000 copies/cell)  Inducible Proteins o Synthesized at variable rates dependent on cells circumstances (regulated)  Eg/ regulatory proteins (often rate <10 copies per cell) o β-galactosidase o Galactoside permease o Thiogalactoside transacetylase  β-galactosidase (β-gal) o A sugar found in milk o Bacteria use forms of glucose (eg/ starch) as their primary carbon source o If there’s no glucose, they can use alternative carbon sources o E. coli can use lactose because it has the enzyme β-galactosidase 1 Biochem 2B03 Jasmyn Lee o β-gal is an inducible enzyme o No lactose  very little β-galactosidase o Add lactose  abundant β-galactosidzse  Jacob and Monod used genetics to study this process: o Isolation of mutant cells that can’t use lactose as carbon source o
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