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CHAPTER 18 REGULATION OF GENE EXPRESSION I. II. III. Student misconceptions 1. Many students have difficulty mastering the distinction between repressible and inducible operons and enzymes. They may fail to recognize the significance of this distinction in the control of prokaryotic metabolism. 2. Students may find it hard to grasp the idea of epigenetic inheritance. They may not understand how modifications to the chromosome that do not alter the sequence of bases can still be passed on to subsequent generations of offspring. 3. Students may find the large number of control points regulating eukaryotic gene expression bewildering. It is important to remind them of the significance of these mechanisms in allowing exquisite control of gene expression during development and in changing environments. Pre-test to identify student misconceptions prior to addressing the material covered in Chapter 18 1. Identify each statement as TRUE or FALSE. a. In an inducible operon, the regulatory protein is synthesized in inhibitory form. True b. In a repressible operon, a specific small molecule binds to the regulatory protein to change it to the inactive form. False c. Repressible enzymes generally function in anabolic pathways. True d. Inducible enzymes generally function in synthetic pathways that produce end products from raw materials. False 2. Identify each statement as TRUE or FALSE. a. Methylation may turn off the expression of a paternal gene for the lifetime of an individual. True b. In prokaryotes, coordinately controlled genes are united by control elements; in eukaryotes, they are united by location. False c. During embryonic development, a cytoplasmic enzyme may cleave poly-A tails from mRNAs to initiate their translation. False d. Ubiquitin tags a protein for degradation. True How can instructors address and correct the misconceptions that students have about the regulation of gene expression? 1. When teaching about repressible and inducible operons, remind students of the role of each type of operon in cell metabolism. This will help students understand the significance of these forms of negative gene regulation, rather than focusing on the memorization of detail. Student Misconceptions for Campbell/Reece Biology, 8th Edition, © Pearson Education, Inc. 18-1 IV. V. 2. Explaining some of the fascinating examples of epigenetic inheritance, including the effects of imprinting in human development, may motivate students to gain a clearer understanding of this concept. Haig (1993) discusses how genetic conflict and imprinting contribute to many of the problems with human pregnancy, including pre-eclampsia and gestational diabetes. 3. Illustrate the coordinate control of gene expression in eukaryotes by describing the activation of related genes that are stimulated by a particular hormone. The text describes the monthly cycle of activation by estrogen of a group of genes, stimulating cell division in uterine cells to prepare the uterus for pregnancy. Post-test to identify whether students have corrected their misconceptions 1. Illustrating your explanation with suitable examples, explain why repressible enzymes generally function in anabolic pathways, whereas inducible enzymes usually function in catabolic pathways. 2. Using an example of activation by a steroid hormone, explain how gene expression in a eukaryotic cell can be coordinately controlled. 3. Explain how the translation of mRNAs stored in the cytoplasm during oogenesis may be initiated following fertilization. Reference Haig, D. (1993). Genetic conflicts in human pregnancy. Quarterly Review of Biology, 68, 495–532. Student Misconceptions for Campbell/Reece Biology, 8th Edition, © Pearson Education, Inc. 18-2