Chapter 13 Study Guide

Chapter 13 Study Guide - Study Guide 13 UNIT III: - Meiosis...

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Study Guide 13 UNIT III: - Meiosis (and Genetic Variation) - Mendel & the Gene (linkage and crossing over) - How Do Genes Work ( DNA = genes; the genetic code) - DNA Synthesis ... (Replication) - Transcription and Translation - Control of Gene Expression in Bacteria - Control of Gene Expression in Eukaryotes A. Controlling Gene Expression in Bacteria 20400. Overview Gene expression is defined here as the synthesis of the final product of the information coded by a gene. It does not include controls on the activities of finished gene products (e.g., allosteric regulation of enzymes). Thus, the control of rRNA gene expression would be assayed by measuring the amount and rate of synthesis of rRNA in the cell. Likewise, the control of expression of the gene for glucose hexokinase (the first glycolytic enzyme) would be assayed by measuring the amount and rate of synthesis of the enzyme. If you detected that the levels of an enzyme rose during development of an organism, or in response to some chemical treatment, you would want to know at what point in the pathway to making the enzyme is regulation actually taking place. An increase in the amount of enzyme present (or the amount synthesized per unit time) occur by: - increasing the rate of transcription of the gene for the enzyme, making more mRNA available, - decreasing the rate of mRNA degradation, also making more mRNA available, - increasing the rate of translation by increasing the rate of loading of ribosomes on the mRNA, - increasing the rate of translation by increasing the rate of elongation of the polypeptide, - decreasing the rate of degradation of the protein, Theoretically one or more of the steps above might be controlled. In bacteria, gene expression is regulated at post-translational , translational and transcriptional levels ( Fig, 17.1 ), the most common being transcriptional control, usually with a molecular on/off switch. Since prokaryotes do not undergo development in the familiar way of higher organisms, gene expression is usually regulated in response to environmental chemicals (e.g., nutrients) or the buildup of excess internal metabolites . 2. The Control of Gene Expression by regulating transcription in Bacteria Gene regulation was first seen in bacteria by investigators like Jacob & Monod who studied the effects of mutations. As with bread mold, many mutations were found to affect individual enzymes in known biochemical pathways. These were called constitutive mutations . But some mutations were discovered that caused a drop in the levels of multiple enzymes in the same biochemical pathway. Because these mutations affected more than one enzyme, it was hypothesized that a regulatory mutation that had affected a gene that controlling the production of groups of related enzymes. In fact, genes performing related functions are often coordinately regulated. In bacteria, this is facilitated by the organization of multiple genes into
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This note was uploaded on 11/22/2009 for the course BIO SCI 150 taught by Professor Geraldbergstrom during the Spring '08 term at Wisconsin Milwaukee.

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Chapter 13 Study Guide - Study Guide 13 UNIT III: - Meiosis...

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