All genes are not "on" all the time. using the metabolic needs of e. coli, explain why not. 2. what are the two main ways of controlling metabolism in bacterial cells? 3. feedback inhibition is a recurring mechanism throughout biological systems. in the case of e. coli regulating tryptophan synthesis, is it positive or negative inhibition? explain your choice. 4. what is a promoter? 5. what is the operator? what does it do? 6. what is an operon? ap biology reading guide chapter 18: regulation of gene expression fred and theresa holtzclaw copyright © 2010 pearson education, inc. - 2 - 7. list the three components of an operon, and explain the role of each one. 8. how does a repressor protein work? 9. what are regulatory genes? 10. distinguish between inducible and repressible operons, and describe one example of each type. 11. label this sketch of the lac operon with the terms at right. know the function of each structure.