1. 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?

1. All genes are not 'on' all the time. Using the metabolic needs of E. coli, E. coli regulate their gene expression to reserve resources when the environment is giving them what they need. E. coli feed on tryptophan, they produce it when tryptophan is low in the environment and they stop the production when it is abundant in their environment.

2. The two main ways of controlling metabolism in bacterial cells include;

to adjust the activity of present enzymes to adjust production level of an enzyme

3. E. coli is negative inhibition because it involves an operon being switched off by active form of repression protein.

4. A promoter is a site where RNA polymerase can bind to DNA and begin transcription

5. The operator is the 'on switch' for gene replication. it is positioned within the promoter or between the promoter and enzyme coding genes. it controls the access of RNA polymerase to the genes.

6. An operon is the functioning unit of DNA containing a cluster of genes under the control of a single promoter.