Question

18) What is the role of CAP and cAMP and what is inducer exclusion? 19) How do restriction enzymes cleave DNA? 20) What is a vector and how are plasmids used to create recombinant DNA? Make sure you understand the role of restriction enzymes, DNA ligase and plasmids. 21) What is Southern Blotting and what is its purpose? 22) What is gene therapy and what benefits does it have?

Answer 1

1. The CAP binding site is a positive regulatory site. When catabolite activator protein (CAP) is bound to this site, it promotes transcription by helping RNA polymerase in binding to the promoter.
2. CAP binds to a region of DNA just before the lac operon promoter and helps RNA polymerase attach to the promoter, driving high levels of transcription.
3. CAP is regulated by a small molecule called cyclic AMP (cAMP).
4. Cyclic adenosine monophosphate (cAMP, cyclic AMP, or 3',5'-cyclic adenosine monophosphate) is a second messenger important in many biological processes.
5. When glucose levels are low, cAMP acts as a signal. cAMP binds to CAP, changing its shape and making it able to bind DNA and promote transcription.
6. When Glucose is present and lactose is absent, no transcription of the lac operon occurs because the lac repressor remains bound to the operator and prevents transcription by RNA polymerase. The cAMP levels are low because glucose levels are high, so CAP is inactive and cannot bind DNA.
7. Inducer exclusion is a form of repression where a transcriptional inducer is excluded from the cell (or nucleus in eukaryotes) to prevent it from functioning. A good example of inducer exclusion involves the E. coli lac operon. Lactose is the inducer of the operon, and glucose is a carbon source preferred to lactose.
8. When glucose and lactose are both present in the medium, induction of the lactose operon is prevented to consume glucose first.