Draw 8 boxes on your paper Gene regulation accounts for some of the phenotypic differences between organisms with similar genes 20052006 Gene regulation in bacteria Control of gene expression enables individual bacteria to adjust their metabolism to environmental change ID: 780405
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Slide1
3.B.1 Gene Regulation
Gene regulation results in differential gene expression, leading to cell specialization.
Draw 8 boxes on your paper
Slide2Gene regulation accounts for some of the phenotypic differences between organisms with similar genes.
Slide32005-2006
Gene regulation in bacteria
Control of gene expression enables individual bacteria to adjust their metabolism to environmental change
Cells vary amount of specific enzymes by
regulating gene transcription
turn
genes on
or turn genes offex. if you have enough tryptophan in your cell then you don’t need to make enzymes used to build tryptophanwaste of energyturn off genes which codes for enzymes
Slide4Box #1
What is gene regulation?
Slide5Slide6Gene expression can involve:
Slide72005-2006
So how can genes be turned off?
First step in protein production?
transcription
stop RNA polymerase!
Repressor protein
binds to DNA near promoter region blocking RNA polymerase
binds to
operator
site on DNA
blocks transcription
Slide8Box # 2
How do you regulate genes?
Slide9Regulatory sequences are stretches of DNA that interact with regulatory proteins to control transcription.
Slide10Operons are a type of regulatory sequence consisting of clusters of genes under the control of a single regulatory region.
Slide112005-2006
Genes grouped together
Operon
genes grouped together with related functions
ex.
enzymes in a synthesis pathway
promoter
= RNA polymerase binding site
single promoter controls transcription of all genes in operontranscribed as 1 unit & a single mRNA is madeoperator = DNA binding site of regulator protein
Slide12Operators are segments of DNA that a regulator molecule can bind to.
Slide13Promoters are nucleotide sequences that allow the genes of an operon to be transcribed.
RNA polymerase binds to the promoter region to begin transcription.
Slide14Slide15Repressors
are small regulatory proteins that halt transcription. They bind to the operator region of an operon and prevent RNA polymerase from binding.
Slide16Box # 3
Describe an operon (include the following terms in description, promoter, repressor and operator.)
Slide17Both positive and negative control mechanisms regulate gene expression in bacteria
and viruses.
Slide18Slide19The expression of specific genes can be inhibited by the presence of a repressor
. A repressor binds to the operator site of an operon, preventing RNA polymerase from binding and therefore preventing transcription of the operon (negative control).
Slide20Inducers
are small proteins that stimulate transcription. They bind to
repressors
, inactivating them so that RNA polymerase can bind to the operator and begin transcription.
Slide21Inducer
Repressor
Slide22Box # 4
Compare and contrast inducers and repressors
Slide23Terminators are nucleotide sequences that mark the end of a gene or operon.
Slide24Enhancers are short regions of DNA that can be bound with proteins to enhance transcription.
Slide25Slide26Box # 5
How do enhancers aid transcription?
Slide27A
regulatory gene
is a sequence of DNA encoding a regulatory protein
(such as a repressor) or
RNA.
Slide28Certain genes are continuously expressed; that is, they are always turned “on,” regardless of environmental conditions.
Slide29Example of Prokaryotic Gene Regulation:
The Trp Operon
Slide30The trp operon consists of a group of genes that code for the enzymes necessary to synthesize tryptophan, an amino acid.
Slide31The trp operon is an example of
negative feedback. When there is too much tryptophan, tryptophan itself acts as a corepressor, which activates the repressor that shuts down this operon.
Slide32The trp operon is an example of a
repressible operon; it is usually “on” but can be turned “off” when there is too much tryptophan.
Slide332005-2006
operator
promoter
Repressor protein
model
DNA
TATA
RNA
polymerase
repressor
repressor
repressor protein
Operon
:
operator, promoter & genes they control
serve as a model for gene regulation
gene
1
gene
2
gene
3
gene
4
RNA
polymerase
Repressor protein
turns off gene by blocking RNA polymerase binding site.
Slide342005-2006
operator
promoter
Repressible operon: tryptophan
DNA
TATA
RNA
polymerase
repressor
tryptophan
repressor
repressor protein
repressor
tryptophan – repressor protein
complex
Synthesis pathway model
When excess tryptophan is present, binds to
tryp
repressor protein
& triggers repressor to
bind
to DNA
blocks (represses) transcription
gene
1
gene
2
gene
3
gene
4
RNA
polymerase
conformational change in repressor protein!
Slide352005-2006
Tryptophan operon
What happens when tryptophan is present?
Don’t need to make tryptophan-building enzymes
Tryptophan binds allosterically to regulatory protein
Slide36Box # 6
Draw the trp operon and how its regulated by a repressor
Slide37Example of Prokaryotic Gene Regulation:
The Lac Operon
Slide38The lac operon consists of a group of genes in
e. coli that allow the bacteria to metabolize lactose when lactose is present in the gut of its host.
Slide39When there is no lactose present, e. coli
does not need to produce the enzymes to break down lactose, instead using glucose as its primary nutrient.
Slide40In the absence of lactose, the lac repressor protein is made, which binds to the operator and halts the binding of RNA polymerase.
Slide41In the presence of lactose, an
inducer binds to the repressor, altering its shape so that it is no longer able to bind to the operator. RNA polymerase can now bind and begin transcribing the operon.
Slide42The lac operon is an example of an
inducible operon; it is usually “off” but can be turned “on” in the presence of lactose.
Slide432005-2006
operator
promoter
Inducible operon: lactose
DNA
TATA
RNA
polymerase
repressor
repressor protein
repressor
lactose – repressor protein
complex
lactose
repressor
gene
1
gene
2
gene
3
gene
4
Digestive pathway model
When lactose is present, binds to
lac
repressor protein
& triggers repressor to
release
DNA
induces transcription
RNA
polymerase
conformational change in repressor protein!
Slide442005-2006
Lactose operon
What happens when lactose is present?
Need to make lactose-digesting enzymes
Lactose binds allosterically to regulatory protein
Slide45Box # 7
Describe the lac operon and the inducer
Slide462005-2006
Operon summary
Repressible operon
usually functions in
anabolic
pathways
synthesizing
end productswhen end product is present in excess,cell allocates resources to other uses Inducible operon usually functions in catabolic pathways,
digesting nutrients to simpler moleculesproduce enzymes only when nutrient is availablecell avoids making proteins that have nothing to do, cell allocates resources to other uses
Slide47In eukaryotes, gene expression is complex and control involves regulatory genes, regulatory elements and transcription factors that act in concert.
Slide48Slide49Transcription factors are proteins that bind
to specific DNA sequences and/or other regulatory proteins. They work alone or in complex.
Slide50Some of these transcription factors are activators
(increase expression), while others are repressors (decrease expression).
Slide51The 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.
Slide52Box # 8
What are transcription factors?How do they involved in eukaryotic gene expression?
Slide53Learning Objectives:LO 3.18
The student is able to describe the connection between the regulation of gene expression and observed differences between different kinds of organisms. [See SP 7.1] LO 3.19 The student is able to describe the connection between the regulation of gene expression and observed differences between individuals in a population.
[See
SP 7.1
]
LO 3.20 The student is able to explain how the regulation of gene expression is essential for the processes and structures that support efficient cell function. [See SP 6.2] LO 3.21 The student can use representations to describe how gene regulation influences cell products and function. [See SP 1.4]