Ch 16: Regulation of Gene Expression
- The structural and functional difference is determined by differences in patterns of gene
expression that result in cell type-specific sets of proteins
- Housekeeping genes are expressed in almost all cell types
- Regulated genes are expressed in a controlled way - may or may not be expressed at
any given time or in a given cell type
- The fundamental mechanisms that control gene expression are common to all
multicellular eukaryotes
- However, prokaryotic systems are limited almost exclusively to short-term
response to environmental changes
- Eukaryotic cells exhibit both short-term responses and long-term differentiation
- Transcriptional regulation: the fundamental level of control, determines which genes are
transcribed into mRNA
- Posttranscriptional regulation: additional controls fine-tune regulation by affecting the
processing of mRNA
- Translational regulation: translation into proteins
- Posttranslational regulation: the lifespan and activity of the proteins themselves
- These regulatory mechanisms tailor the production of all cellular molecules
● 16.1: Regulation of Gene Expression in Prokaryotes
○ Prokaryotes are relatively simple, single-celled organisms with generations that
take a matter of minutes
○ Prokaryotic cells undergo rapid and reversible alterations in biochemical
pathways that allow them to adapt quickly to changes in their environment
○ Example: Escherichia coli
■ E coli catabolize a number of sugars and other molecules to provide
carbon and energy for the cell
■ When lactose (one of those sugar) is present
● The bacterium makes three proteins for catabolizing the sugar,
lactose
● Three regulated genes for those proteins (for lactose catabolism)
are expressed
■ When lactose is not present
● It does not make those proteins
● The three regulated genes for lactose catabolism are not express
■ Result: When the environment changes, some metabolic processes are
stopped and others are started
● usually, turning off the genes for the metabolic processes not
needed and turning on the genes for the new metabolic processes
● This regulation of genes conserves energy for the bacterium
○ Some Regulated Genes Occur in Clusters Called Operons
■ Except for housekeeping genes, genes in the prokaryotic genome are
regulated
■ SOME regulated genes that occur singly
, ● The gene is transcribed by RNA polymerase to produce a mRNA
molecule that is translated to produce a single polypeptide
● Transcription unite: the segment of DNA from the initiation point of
transcription to the termination point of transcription
○ The transcription unit corresponds to the mRNA-coding
sequence of that gene
■ Other regulated genes that occur in an associated cluster
● Each cluster constitute one transcription unit
○ The set of genes in the cluster is transcribed into a single
mRNA molecule
○ Translation of the mRNA produces polypeptides
corresponding to each of the genes in the transcription unit
■ Operon model: the organization of genes in a cluster provides a means
for efficient coordinate regulation of those genes
■ Operon: a cluster of prokaryotic organized into a single transcription unit
and its associated regulatory sequences
■ Regulatory sequences: DNA sequences involved in the regulation of a
gene or genes
● Proteins bind to those sequences to control the transcription of the
gene or genes
● DNA-binding protein: a protein that binds to a specific DNA
sequence
○ Bind by interactions between particular amino acid regions
in the three-dimensional shape of the protein and specific
base pairs of the DNA
● Promotor: the site to which RNA polymerase binds to begin
transcription
● Operator: a short segment to which a specific protein binds to
affect the expression of the operon
■ Regulatory protein: a DNA-binding protein that binds to a regulatory
sequence and affects the expression of an associated gene or genes
● Repressor: when active, prevents the operon genes from being
expressed
● Activator: when active, turns on the expression of the genes
○ The lac Operon for Lactose Metabolism Is Transcribed When an Inducer
Inactivates a Repressor
, ■ Lactose is a sugar: the protein products of three genes, lacZ, lacY, and
lacA are involved in lactose catabolism
● They are adjacent to one another in the order Z-Y-A and
constitute a single transcription unit
■ Promoter
● Upstream of lacZ
● The genes are transcribed as a unit into a single mRNA starting
with the lacZ gene
■ lacZ gene
● Encodes the enzymes ß-galactosidase, which has two catalytic
activities
○ 1st activity: hydrolysis of the disaccharide sugar (lactose)
into the monosaccharide sugars (glucose and galactose)
■ Those sugars are catabolized and produce energy
for the cell
○ 2nd activity: converting lactose to allolactose, and an
isomer of lactose
■ lacY gene
● Encodes a permease (not an enzyme), a protein that actively
transports lactose into the cell
■ lacA gene
● Encodes a transacetylase enzyme
○ Unclear function
■ Lac operon: a cluster of genes and adjacent sequences that control their
expression
■ Operator
● Between the promoter and the lacZ
● Regulate transcription
■ Lac repressor
● Encoded by the regulatory gene lacI, nearby but separate from the
lac operon
● The lac operon is a negatively regulated system controlled by a
regulatory protein (lac repressor)
- The structural and functional difference is determined by differences in patterns of gene
expression that result in cell type-specific sets of proteins
- Housekeeping genes are expressed in almost all cell types
- Regulated genes are expressed in a controlled way - may or may not be expressed at
any given time or in a given cell type
- The fundamental mechanisms that control gene expression are common to all
multicellular eukaryotes
- However, prokaryotic systems are limited almost exclusively to short-term
response to environmental changes
- Eukaryotic cells exhibit both short-term responses and long-term differentiation
- Transcriptional regulation: the fundamental level of control, determines which genes are
transcribed into mRNA
- Posttranscriptional regulation: additional controls fine-tune regulation by affecting the
processing of mRNA
- Translational regulation: translation into proteins
- Posttranslational regulation: the lifespan and activity of the proteins themselves
- These regulatory mechanisms tailor the production of all cellular molecules
● 16.1: Regulation of Gene Expression in Prokaryotes
○ Prokaryotes are relatively simple, single-celled organisms with generations that
take a matter of minutes
○ Prokaryotic cells undergo rapid and reversible alterations in biochemical
pathways that allow them to adapt quickly to changes in their environment
○ Example: Escherichia coli
■ E coli catabolize a number of sugars and other molecules to provide
carbon and energy for the cell
■ When lactose (one of those sugar) is present
● The bacterium makes three proteins for catabolizing the sugar,
lactose
● Three regulated genes for those proteins (for lactose catabolism)
are expressed
■ When lactose is not present
● It does not make those proteins
● The three regulated genes for lactose catabolism are not express
■ Result: When the environment changes, some metabolic processes are
stopped and others are started
● usually, turning off the genes for the metabolic processes not
needed and turning on the genes for the new metabolic processes
● This regulation of genes conserves energy for the bacterium
○ Some Regulated Genes Occur in Clusters Called Operons
■ Except for housekeeping genes, genes in the prokaryotic genome are
regulated
■ SOME regulated genes that occur singly
, ● The gene is transcribed by RNA polymerase to produce a mRNA
molecule that is translated to produce a single polypeptide
● Transcription unite: the segment of DNA from the initiation point of
transcription to the termination point of transcription
○ The transcription unit corresponds to the mRNA-coding
sequence of that gene
■ Other regulated genes that occur in an associated cluster
● Each cluster constitute one transcription unit
○ The set of genes in the cluster is transcribed into a single
mRNA molecule
○ Translation of the mRNA produces polypeptides
corresponding to each of the genes in the transcription unit
■ Operon model: the organization of genes in a cluster provides a means
for efficient coordinate regulation of those genes
■ Operon: a cluster of prokaryotic organized into a single transcription unit
and its associated regulatory sequences
■ Regulatory sequences: DNA sequences involved in the regulation of a
gene or genes
● Proteins bind to those sequences to control the transcription of the
gene or genes
● DNA-binding protein: a protein that binds to a specific DNA
sequence
○ Bind by interactions between particular amino acid regions
in the three-dimensional shape of the protein and specific
base pairs of the DNA
● Promotor: the site to which RNA polymerase binds to begin
transcription
● Operator: a short segment to which a specific protein binds to
affect the expression of the operon
■ Regulatory protein: a DNA-binding protein that binds to a regulatory
sequence and affects the expression of an associated gene or genes
● Repressor: when active, prevents the operon genes from being
expressed
● Activator: when active, turns on the expression of the genes
○ The lac Operon for Lactose Metabolism Is Transcribed When an Inducer
Inactivates a Repressor
, ■ Lactose is a sugar: the protein products of three genes, lacZ, lacY, and
lacA are involved in lactose catabolism
● They are adjacent to one another in the order Z-Y-A and
constitute a single transcription unit
■ Promoter
● Upstream of lacZ
● The genes are transcribed as a unit into a single mRNA starting
with the lacZ gene
■ lacZ gene
● Encodes the enzymes ß-galactosidase, which has two catalytic
activities
○ 1st activity: hydrolysis of the disaccharide sugar (lactose)
into the monosaccharide sugars (glucose and galactose)
■ Those sugars are catabolized and produce energy
for the cell
○ 2nd activity: converting lactose to allolactose, and an
isomer of lactose
■ lacY gene
● Encodes a permease (not an enzyme), a protein that actively
transports lactose into the cell
■ lacA gene
● Encodes a transacetylase enzyme
○ Unclear function
■ Lac operon: a cluster of genes and adjacent sequences that control their
expression
■ Operator
● Between the promoter and the lacZ
● Regulate transcription
■ Lac repressor
● Encoded by the regulatory gene lacI, nearby but separate from the
lac operon
● The lac operon is a negatively regulated system controlled by a
regulatory protein (lac repressor)
