Download Essential knowledge 3.B.1

Gene regulation results in differential gene
expression, leading to cell specialization.
Regulatory sequences are stretches of DNA that
interact with regulatory proteins to control
transcription.
• Promoters
• Terminators
• Enhancers
 A regulatory gene is a sequence of DNA
encoding a regulatory protein or RNA.
 Find the regulator gene on the next slide.
What does it do?
Fig. 18-3
trp operon
Promoter
Promoter
DNA
trpR
Regulatory
gene
mRNA
5
Protein
Genes of operon
trpE
3
Operator
Start codon
mRNA 5
RNA
polymerase
Inactive
repressor
E
trpD
trpB
trpA
B
A
Stop codon
D
C
Polypeptide subunits that make up
enzymes for tryptophan synthesis
(a) Tryptophan absent, repressor inactive, operon on
DNA
No RNA made
mRNA
Active
repressor
Protein
trpC
Tryptophan
(corepressor)
(b) Tryptophan present, repressor active, operon off
The expression of specific genes can be turned on by
the presence of an inducer.
 The expression of specific genes can be inhibited by
the presence of a repressor.
 Inducers and repressors are small molecules that
interact with regulatory proteins and/or regulatory
sequences
 Regulatory proteins inhibit gene expression by binding
to DNA and blocking transcription (negative control).
 Regulatory proteins stimulate gene expression by
binding to DNA and stimulating transcription (positive
control) or binding to repressors to inactivate
repressor function.
 Certain genes are continuously expressed; that is, they
are always turned “on,” e.g., the ribosomal genes.

Fig. 18-3
trp operon
Promoter
Promoter
DNA
trpR
Regulatory
gene
mRNA
5
Protein
Genes of operon
trpE
3
Operator
Start codon
mRNA 5
RNA
polymerase
Inactive
repressor
E
trpD
trpC
trpB
trpA
B
A
Stop codon
D
C
Polypeptide subunits that make up
enzymes for tryptophan synthesis
(a) Tryptophan absent, repressor inactive, operon on
DNA
No RNA made
mRNA
Active
repressor
Protein
Tryptophan
(corepressor)
(b) Tryptophan present, repressor active, operon off
Is this negative
or positive
control?
Fig. 18-4a
Regulatory
gene
Promoter
Operator
lacI
DNA
lacZ
No
RNA
made
3
mRNA
Protein
5
RNA
polymerase
Active
repressor
Is this
positive or
negative
control?
(a) Lactose absent, repressor active, operon off
 http://highered.mcgraw-
hill.com/sites/9834092339/student_view0/c
hapter16/regulatory_proteins__regulation_by
_repression.html
1. Transcription factors bind to specific DNA
sequences and/or other regulatory proteins.
2. Some of these transcription factors are
activators (increase expression), while others
are repressors (decrease expression).
3. The combination of transcription factors
binding to the regulatory regions at any one
time determines how much, if any, of the
gene product will be produced.
Fig. 18-9-3
Promoter
Activators
DNA
Enhancer
Distal control
element
Gene
TATA
box
General
transcription
factors
DNA-bending
protein
Group of
mediator proteins
RNA
polymerase II
RNA
polymerase II
Transcription
initiation complex
RNA synthesis
 http://highered.mcgraw-
hill.com/sites/9834092339/student_view0/c
hapter16/transcription_complex_and_enhanc
ers.html
 Gene
regulation accounts for some of the
phenotypic differences between organisms
with similar genes.
A variety of intercellular
and intracellular signal
transmissions mediate gene
expression
 Cytokines
regulate
gene expression to
allow for cell
replication and
division.
 Mating
pheromones in
yeast trigger mating gene
expression.
 Two
haploid yeast of
opposite mating types
secrete pheromones,
grow projections and
mate.
 Ethylene
levels cause changes in the
production of different enzymes, allowing
fruits to ripen.
 Seed
germination and gibberellin
 Gibberellins (GAs) are plant hormones that
regulate growth and influence various
developmental processes, including stem
elongation, and germination
Ex 1: HOX genes and their role in development.
 Hox genes are a group of related genes that
control the body plan of the embryo along
the anterior-posterior (head-tail) axis.
 Ex
2: P53 is a tumor suppressor
protein
 p53 is crucial in multicellular
organisms, where it regulates the
cell cycle and, thus, functions as
a tumor suppressor that is
involved in preventing cancer.
 As such, p53 has been described
as "the guardian of the genome
because of its role in conserving
stability by preventing genome
mutation
 Morphogenesis
“shape” and beginnign--is the
biological process that causes an organism to
develop its shape
 Example 3: morphogen is a substance
governing the pattern of tissue development
in the process of morphogenesis, and the
positions of the various specialized cell types
within a tissue.
 More precisely, a morphogen is a signaling
molecule that acts directly on cells to
produce specific cellular responses depending
on its local concentration.