Gene Regulation - Operon Examples - PDF
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This document provides an overview of bacterial gene regulation, particularly concerning operon examples such as the lactose and tryptophan operons. The presentation details the structure of genes and mRNA, providing insight to the control mechanisms. The information is organized for learning and understanding.
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Gene Regulation Operon examples Regulation of Bacterial Gene Expression Constitutive enzymes are expressed at a fixed rate. Other enzymes are expressed only as needed. – Repressible enzymes – Inducible enzymes Structure of a Gene and mRNA Operon Ex...
Gene Regulation Operon examples Regulation of Bacterial Gene Expression Constitutive enzymes are expressed at a fixed rate. Other enzymes are expressed only as needed. – Repressible enzymes – Inducible enzymes Structure of a Gene and mRNA Operon Examples Lactose Operon Tryptophan Operon Regulator protein DNA Binding Protein binds operator site blocks RNA polymerase Figure 8.12, step 1 Example: Inducible Lac Operon No lactose present, Cell does not need enzymes to catabolize Figure 8.12, step 2a Induction refered carbon source absent (glucose). actose present, Cell needs enzymes to catabolize Figure 8.12, step 3a Lac operon control Repressor binding prevents RNAP binding promoter An activating transcription factor found to be required for full lac operon expression: CAP (or Crp) lac operon – activator and repressor CAP = catabolite activator protein CRP = cAMP receptor protein Cofactor binding alters conformation CAP binds cAMP, induces allosteric changes glucose glucose cAMP cAMP CAP CAP lac operon no mRNA mRNA Carbohydrate Metabolism global control Figure 8.14a Present Figure 8.14b Regulation of Gene Expression Figure 8.13 Summarize How can the Lac operon be both Positively and Negatively regulated? What is the difference? What is the Positive Regulator and its effector? What is the Negative Regulator and its effector? Example: Repressible Tryptophan Operon ell needs tryptophan, so enzymes are transcribed Figure 8.12, step 2b Repression l does not need more tryptophan, so enzymes are not transcribed dback! Figure 8.12, step 3b Explain it Explain to your Neighbor – How lac operon is inducible? – How Tryptophan operon is repressible? – What is the difference? – Is the Trp operon an example of positive or negative regulation? Why? Figure 12.5 Next Time Start Viruses
