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Chapter 14 – Gene Regulation

Chapter 14 – Gene Regulation - Chapter 14...

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Chapter 14 – Gene Regulation I) Gene Regulation In Bacteria And Eukaryotes: An Overview a. Transcriptional Level Control i. Requirement of bacterial gene regulation is production of enzymes and other proteins ii. This mechanism rapidly turns genes on and off as units allowing synthesis of only the gene products needed at any particular time 1. Requires rapid turn over of mRNA molecules to prevent accumulation of continuing and translating of messages b. Bacteria regulate enzyme levels by diluting protein molecules in subsequent cell divisions breaking down unnecessary i. Protein digesting enzymes recycle amino acids by breaking down proteins no longer needed only when cells are starved c. Proteins are usually rapidly converted from an inactive to an active state d. IGF2 – insulin-like growth factor 2 i. Base substitution mutation in the IGF2 gene makes genes 3 times as more active II) Gene Regulation in Bacteria a. Constitutive Genes i. Genes which are constantly transcribed ii. Described as constitutively expressed b. Metabolic Activity controlled in two ways i. Regulating the activity of certain enzymes ii. Regulating the number of enzyme molecules present c. Operons in Bacteria Facilitate The Coordinated Control of Functionally related genes i. Jacob and Monod Experiment 1. E. Coli cells growing on lactose has several thousand B- galactosidase molecules, lactose permease (aids in transport of lactose across plasma membrane), and galactoside transacetylase .
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2. Operon a. Gene complex consisting of a group of structural genes with related functions and closely linked DNA sequences ii. Transcription of Operon 1. Begins as RNA polymerase binds to a single promoter region 2. Each enzyme coding sequence on mRNA contains its own start and stop codons a. Translated into 3 separate polypeptides 3. Operator and repressor protein are closely bound together (repressed state of operator) a. Operator i. Switch that controls mRNA synthesis b. Repressor protein i. Encoded by a repressor gene and stops mRNA synthesis of Operon 4. Certain substance (lactose) induces transcription of Operon a. Repressor protein contains an allosteric site that allows allolactose to bind to it b. Binding of allolactose to repressor alters the shape of the protein c. Repressor molecules have allolactose bound to them are
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Chapter 14 – Gene Regulation - Chapter 14...

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