Figure 18.19 Regulation of a metabolic pathway

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