1. General concepts of gene regulation
2. The Lac and Trp operons
3. Catabolite repression

1. The concepts covered here can be reviewed in your textbook, pages 218-219 (The Regulation of Bacterial Gene Expression), and your lecture notes.

2. When a bacterial gene is used to synthesize a protein, we say that the gene is expressed. At any given time, a bacterium will not be expressing all of its genes. On a piece of paper, write some reasons why?

3. Bacteria can regulate their genes in two main ways, they can turn them on or off, or they can adjust the rate of transcription. Mostly, they regulate genes by turning them off. There are two types of genes in bacteria - constitutive and regulated. On a piece of paper, write down the definitions of those two types of genes. Make a list of what you think might be some constitutive and some regulated genes (consult your textbook and notes).

4. Bacterial genes are often organized as operons. On a piece of paper, write down the definition of operon. Using your textbook and notes, draw a schematic of bacterial operon with 4 genes. Make sure that you have the following parts in your operon:

• The regulator gene (usually noted as I)
• The promoter (usually noted as P)
• The operator (usually noted as O)
• The structural genes (in this example, let's make them D, F, R, and T)
• Draw arrows pointing to I, P and O and write out the functions of those parts of the operon
• Draw the mRNA that will result from this operon when it is transcribed
• Draw the proteins that will be made when this operon is expressed
• In what proportion will the proteins be made?

5. Most operons are regulated using a repressor. Write the definition of repressor. Draw 2 diagrams of your operon from point 4 above:

• Operon in ON mode - RNA polymerase attached, Repressor not present. Make sure your RNA polymerase is attached to the correct structure in the operon.
• Operon in OFF mode - RNA polymerase attached, Repressor present. Make sure your RNA polymerase and repressor are attached to the correct structures in the operon.
• As you are looking at that diagram answer the question - how does a bacterial repressor turn an operon OFF?

6. If you feel that you have mastered the concepts on this page, you can move to the next topic of this sub-unit, which explores the regulation of two bacterial operons.