1. The control of gene
expression enable individual
bacteria to adjust their
metabolism to environmental
change

2. Regulation of a Metabolic Pathway

3. Operon : consists of a
closely related group of
genes that act together
and code for the enzymes
that control a particular
metabolic pathway; con-
sists of an operator, pro-
moter, and the genes they
control

4. The trp operon: regulated synthesis of repressible enzymes

5. The trp operon: regulated synthesis of repressible enzymes

6. The “switch” for turning
the genes off and on is
called an operator. It is
positioned within the pro-
moter or between the pro-
moter and enzyme-encoding
genes, controlling access to
the genes.

7. What determines if the operator is on?
By itself, it is on – RNA polymerase can bind to the promoter. It can be switched off by a protein called a repressor.

8. The trp operon: regulated synthesis of repressible enzymes

9. The repressor is a product
of a regulatory gene. These
are transcribed continuously, although at a
low rate.

10. Tryptophan (trp) is synthe-
sized from E. coli from a pre-
cursor molecule in a series
of steps. The trp operon is
said to be a repressible operon because transcription
of it is inhibited when a specific small molecule (tryptophan) binds to a regulatory protein

11. The lac operon: regulated synthesis of inducible enzymes

12. The lac operon: regulated synthesis of inducible enzymes

13. In contrast, an inducible
operon, like the lac operon,
is stimulated (i.e. induced)
when a specific small
molecule interacts with a
regulatory protein.

14. The disaccharide, lactose,
is available to E. coli if the
human host drinks milk.
The bacteria can absorb the
lactose and break it down
for energy. Lactose metabolism
begins with the hydrolysis
of lactose into its two
monosaccharides

15. The gene for beta
galactosidase is part of an operon, the lac operon, that includes two other genes coding for proteins that function in lactose metabolism

16. The enzyme that catalyzes
this reaction is called
beta galactosidase. In the
presence of lactose it can
increase 1000x in 15 min.

17. Positive control: cAMP receptor protein
CAP
CAP

18. Positive control: cAMP receptor protein
CAP
CAP