Chapter 16 lac operon
Gene Control in Prokaryotes
1. The structure and function of the lac operon
2. The regulation of the lac operon
3. Inducible and repressible enzymes
The structure and function of the lac operon
An operon is a cluster of genes controlled by a single promoter, allowing for coordinated expression.
This system is particularly efficient in prokaryotes for regulating the expression of multiple genes
simultaneously.
Operons consist of several key components:
Regulatory gene(s) - These encode proteins that regulate the expression of the structural
genes.
A promoter region - This is the site where RNA polymerase binds to initiate transcription.
An operator region - This is a sequence where regulatory proteins (like repressor proteins)
can bind.
Structural gene(s) - These genes code for proteins, typically enzymes.
The lac operon is a group of genes in the bacterium Escherichia coli that control the metabolism of
lactose, allowing them to use lactose as an energy source when glucose is scarce. The genes are
controlled by the same promoter region and are transcribed together.
The lacI regulatory gene of the lac operon codes for a repressor protein that can inhibit and control
the lac operon's activity.
, The lac operon includes three structural genes essential for lactose metabolism:
Gene Enzyme Function
lacZ β-galactosidase Breaks down lactose into glucose and galactose
Lactose
lacY Transports lactose into the cell
permease
lacA Transacetylase Modifies lactose or its by-products
The regulation of the lac operon by lactose
The lac operon is designed to conserve energy by producing lactose-metabolising enzymes only
when lactose is present.
How the lac operon functions when lactose is absent
When lactose is absent:
1. The repressor protein binds to the operator region.
2. RNA polymerase is blocked from the promoter region.
3. RNA polymerase can't transcribe the structural genes.
4. The enzymes for lactose metabolism aren't produced.
How the lac operon functions when lactose is present
Gene Control in Prokaryotes
1. The structure and function of the lac operon
2. The regulation of the lac operon
3. Inducible and repressible enzymes
The structure and function of the lac operon
An operon is a cluster of genes controlled by a single promoter, allowing for coordinated expression.
This system is particularly efficient in prokaryotes for regulating the expression of multiple genes
simultaneously.
Operons consist of several key components:
Regulatory gene(s) - These encode proteins that regulate the expression of the structural
genes.
A promoter region - This is the site where RNA polymerase binds to initiate transcription.
An operator region - This is a sequence where regulatory proteins (like repressor proteins)
can bind.
Structural gene(s) - These genes code for proteins, typically enzymes.
The lac operon is a group of genes in the bacterium Escherichia coli that control the metabolism of
lactose, allowing them to use lactose as an energy source when glucose is scarce. The genes are
controlled by the same promoter region and are transcribed together.
The lacI regulatory gene of the lac operon codes for a repressor protein that can inhibit and control
the lac operon's activity.
, The lac operon includes three structural genes essential for lactose metabolism:
Gene Enzyme Function
lacZ β-galactosidase Breaks down lactose into glucose and galactose
Lactose
lacY Transports lactose into the cell
permease
lacA Transacetylase Modifies lactose or its by-products
The regulation of the lac operon by lactose
The lac operon is designed to conserve energy by producing lactose-metabolising enzymes only
when lactose is present.
How the lac operon functions when lactose is absent
When lactose is absent:
1. The repressor protein binds to the operator region.
2. RNA polymerase is blocked from the promoter region.
3. RNA polymerase can't transcribe the structural genes.
4. The enzymes for lactose metabolism aren't produced.
How the lac operon functions when lactose is present
