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Solomon IM Ch 14

Solomon IM Ch 14 - ,Berg,andMartinsBiology,9thEdition 14...

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Instructor’s Manual for Solomon, Berg, and Martin’s Biology, 9 th Edition 138 14 Gene Regulation Lecture Outline I. Gene regulation in prokaryotes and eukaryotes: An overview A. Bacteria grow quickly, have short lifespans, and have an independent existence. 1. Economy characterizes regulatory mechanisms. 2. Transcriptional level control is most efficient. B. Eukaryotes have gene regulation based on the specificity of the needs of the cell. II. Gene regulation in prokaryotes is economical. A. E. coli has 4,288 genes that code for proteins, and over half have known functions. 1. Constitutive genes are those that are constantly needed and therefore constantly transcribed. 2. Regulation of metabolic activity may be accomplished by regulating the activity of enzymes or the quantity of enzymes produced. B. Operons in prokaryotes permit coordinated control of functionally related genes. C. Jacob and Monod isolated genetic mutants to study the lac operon experimentally in 1961. 1. Mutant strains were separated into groups of those with either a mutation that affects the entire mechanism or just one of the three mechanisms. a) E. coli growing on glucose have a low amount of three enzymes necessary for lactose metabolism. b) A mutant strain lacked all three enzymes for lactose metabolism. c) The genes for these enzymes were linked in the lactose operon. (1) An operon is a cluster of functionally related genes under the same regulatory control. d) RNA polymerase binds to a single promoter upstream from the coding sequences. e) A single mRNA molecule is transcribed, carrying the genetic information for all three enzymes. (1) Termination sequences between the three coding sequences results in the synthesis of three separate enzymes, but with 1 shared molecular switch. f) The operator overlaps the promoter and is upstream from the first structural gene. g) A repressor protein binds to the operator in the absence of lactose. h) The regulatory gene coding for the repressor protein is upstream of the operator and promoter. (1) This gene is constitutive (always “on”). (2) In the absence of lactose, the operator is always occupied by the repressor. i) If lactose is present, some molecules are converted to allolactose.
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Chapter 14: Gene Regulation 139 j) Allolactose binds to the allosteric binding site on the repressor protein and blocks its binding to the operator. k) The operator is now “open,” and transcription can proceed. 2. Constitutive genes produce even if lactose is absent, which is a waste of energy. a) Lactose absence led to no formation of repressor protein. b) Map position for this protein was found to be outside of the lac operon. 3. Some had constitutive regulatory genes with map positions within the lac operon. a) These didn’t directly involve any of the three structural genes.
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