Lecture 3: Regulation of bacterial gene expression part 1
Learning outcomes:
1. Principle of prokaryotic gene regulation
2. Strategies of gene regulation
3. The operon
4. Lac operon
5. Control of the lac operon
Background
The lac operon is the first example to show how genes are regulated
At some level, all biology comes down to is regulating gene expression
Gene expression is all about producing transcripts, many of which code for MRNA molecule, which are
translated to proteins
Many MRNA do not encode proteins but encode non-coding RNA molecules, which have numerous
cellular functions
Expression of genes s what biology is about- fundamentally important to understand
Introduction- control of gene expression
Trans-acting factors Cis-acting DNA sequences
Definition Genes (code for protein, Trna, rRNA) the product of - Site that affect the activity only of sequences
which can function on any copy of its target DNA. on its own molecule of DNA or RNA
- In prokaryotes, cis-acting DNA sequence
refers to genes immediately adjacent to
trans-acting factors
Protein, RNA molecule that diffuses away from the operators, promotors, terminators
location of synthesis to act elsewhere DNA sequences that function solely as a
DNA sequence
Only local effects
Further, define genes into:
1. Structural gene
- Gene
- Gene that codes for RNA or protein product other than a regulator
- i.e. metabolic enzyme
2. regulatory gene
- gene that codes for a product (typically a protein) that controls the expression of other genes
(usually at the level of transcription) by binding to particular sites on DNA (cis-acting sequences)
promotors have additional cis-acting DNA sequences in E.coli called operator
- Operators= sites on DNA located upstream the target gene
, Lecture 3: Regulation of bacterial gene expression part 1
- Operators control the promotor- the promotor regulates transcription- essentially the operator
controls gene expression.
This interaction can regulate a target gene either was
- Positive manner= gene on =require activator
- Negative manner= gene off= require repressor
Cell biology is about switching genes on and off at the right time in the prescence of the right stimulus
- i.e. EC or IC signal, nutrients, hormone
Positive control gene expression Negative control gene expression
trans-acting transcription factor activator is required trans-acting repressor protein binds to a cis-acting
to bind at the cis-acting promotor to enable RNA operator to prevent a gene from being expressed
polymerase to initiate transcription absent repressor- gene expressed-gene on by default
absent positive regulator (transcription factor)- gene most common type of regulation in bacteria
inactive- gene off by default
most common type of regulation in eukaryotes
Induction and repression- control of gene expression
gene encode enzyme may be regulated by the concentration of its substrate or product
Bacteria will not synthesise the enzyme of a pathways in the absence of the substrate
- Avoiding waste of energy
- Bacteria will produce the enzyme in the presence of the substrate
Inducible regulation Repressible regulation
gene regulated by presence of substrate (inducer)- vital Gene regulated in the presence of the product of its enzyme
pathway (corepressor).
If bacteria needs an AA, which is in high concentration in
the environment, the bacteria will not switch on the gene
that produces that AA.
- Product inhibits the expression of the gene
required to generate that AA
Importance of gene regulation
Learning outcomes:
1. Principle of prokaryotic gene regulation
2. Strategies of gene regulation
3. The operon
4. Lac operon
5. Control of the lac operon
Background
The lac operon is the first example to show how genes are regulated
At some level, all biology comes down to is regulating gene expression
Gene expression is all about producing transcripts, many of which code for MRNA molecule, which are
translated to proteins
Many MRNA do not encode proteins but encode non-coding RNA molecules, which have numerous
cellular functions
Expression of genes s what biology is about- fundamentally important to understand
Introduction- control of gene expression
Trans-acting factors Cis-acting DNA sequences
Definition Genes (code for protein, Trna, rRNA) the product of - Site that affect the activity only of sequences
which can function on any copy of its target DNA. on its own molecule of DNA or RNA
- In prokaryotes, cis-acting DNA sequence
refers to genes immediately adjacent to
trans-acting factors
Protein, RNA molecule that diffuses away from the operators, promotors, terminators
location of synthesis to act elsewhere DNA sequences that function solely as a
DNA sequence
Only local effects
Further, define genes into:
1. Structural gene
- Gene
- Gene that codes for RNA or protein product other than a regulator
- i.e. metabolic enzyme
2. regulatory gene
- gene that codes for a product (typically a protein) that controls the expression of other genes
(usually at the level of transcription) by binding to particular sites on DNA (cis-acting sequences)
promotors have additional cis-acting DNA sequences in E.coli called operator
- Operators= sites on DNA located upstream the target gene
, Lecture 3: Regulation of bacterial gene expression part 1
- Operators control the promotor- the promotor regulates transcription- essentially the operator
controls gene expression.
This interaction can regulate a target gene either was
- Positive manner= gene on =require activator
- Negative manner= gene off= require repressor
Cell biology is about switching genes on and off at the right time in the prescence of the right stimulus
- i.e. EC or IC signal, nutrients, hormone
Positive control gene expression Negative control gene expression
trans-acting transcription factor activator is required trans-acting repressor protein binds to a cis-acting
to bind at the cis-acting promotor to enable RNA operator to prevent a gene from being expressed
polymerase to initiate transcription absent repressor- gene expressed-gene on by default
absent positive regulator (transcription factor)- gene most common type of regulation in bacteria
inactive- gene off by default
most common type of regulation in eukaryotes
Induction and repression- control of gene expression
gene encode enzyme may be regulated by the concentration of its substrate or product
Bacteria will not synthesise the enzyme of a pathways in the absence of the substrate
- Avoiding waste of energy
- Bacteria will produce the enzyme in the presence of the substrate
Inducible regulation Repressible regulation
gene regulated by presence of substrate (inducer)- vital Gene regulated in the presence of the product of its enzyme
pathway (corepressor).
If bacteria needs an AA, which is in high concentration in
the environment, the bacteria will not switch on the gene
that produces that AA.
- Product inhibits the expression of the gene
required to generate that AA
Importance of gene regulation
