THINK ABOUT IT How Does A Cell Know Which Gene To Express amp Which Gene Should Stay Silent Prokaryotic Gene Regulation To conserve resources prokaryotes regulate their activities producing only those genes necessary for the cell to function ID: 729660
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Slide1
13.4 Gene Regulation and ExpressionSlide2
THINK ABOUT IT
How Does A Cell Know?
Which Gene To
Express
&
Which Gene Should Stay
Silent
?Slide3
Prokaryotic Gene Regulation
@
To conserve resources, prokaryotes regulate their activities, producing only those genes necessary for the cell to function.@
It would be wasteful for a bacterium to produce enzymes that are needed to make a molecule that is readily available from its environment.
(why waste energy if you already have food?)Slide4
Prokaryotic Gene Regulation
What is an
Operon
?
Group of Genes That Operate Together
For Example:E. coli ferments lactoseTo Do That It Needs Three Enzymes (Proteins), It Makes Them All At Once!3 Genes Turned On & Off Together. This is known as the lac Operon (lactose Operon)Slide5
The
Lac
Operon
@The
lac OperonRegulates Lactose Metabolism@It Turns On Only When Lactose Is Present & Glucose is Absent.Lactose is a DisaccharideA Combination of Galactose & Glucose To Ferment Lactose E. coli Must:Transport Lactose Across Cell MembraneSeparate The Two SugarsSlide6
Promoters and Operators
The first is a promoter (P), which is a site where RNA-polymerase can bind to begin transcription.
The other region is called the
operator (O), which is where the
lac
repressor can bind to DNA.Slide7
The
Lac
Repressor Turns Transcription OffSlide8
Lactose Turns the Operon “On”Slide9
Gene Regulation:
lac Operon
Key Concept
:
The lac Genes Are:Turned Off By Repressors AndTurned On By The Presence Of LactoseSlide10
Eukaryotic Cell Specialization
Most Eukaryotic Genes Are
Controlled Individually
And Have Regulatory Sequences That Are
Much More Complex Than Prokaryotic Gene RegulationSlide11
RNA Interference
For years, biologists wondered why cells that contain lots of small RNA molecules, only a few dozen bases long, and don’t belong to any of the major groups of RNA (mRNA,
tRNA
, or
rRNA
)Slide12
RNA Interference
@
Blocking gene expression by means of an
miRNA
silencing complex is known as RNA interference (
RNAi).@ Slide13
Genetic Control of Development
As an embryo develops, different sets of genes are regulated by transcription factors, enhancers, and repressors.
Gene regulation helps cells undergo differentiation, becoming
specialized in structure
and function. Slide14Slide15
Homeotic Genes
Edward B. Lewis was the first to show that a specific group of genes controls the identities of body parts in the embryo of the common fruit fly.
Lewis found that a mutation in one of these genes actually resulted in a fly with a leg growing out of its head in place of an antenna!
These master control genes,
homeobox
genes, activate genes important in cell developmentSlide16
Regulation & Development
Hox
Genes
@Control
Organ & Tissue Development In The Embryo@Mutations Lead To Major ChangesDrosophila With Legs In Place of AntennaeSlide17
Regulation & Development
Hox
Genes
Present In All EukaryotesShows Common AncestryPax 6 hox geneControls eye growth in Drosophila, Mice & ManPax 6 from Mouse Placed In Knee Development Sequence Of Drosophila Developed Into Eye Tissue.Common Ancestor >600M Years AgoSlide18
Regulation & DevelopmentSlide19
Homeobox
and
Hox Genes
Nearly all animals, share the same basic tools for building the different parts of the body.
Common patterns of genetic control exist because all these genes have descended from the genes of common ancestors.Slide20
Environmental Influences
@
In prokaryotes and eukaryotes, environmental factors can influence gene expression.@ Ex: temperature, salinity, nutrient availability
Ex: The
lac
operon in E. coli is switched on only when lactose is the only food source in the bacteria’s environment.Slide21
This type of RNA is used to block gene expression
rRNA
tRNA
mRNA
miRNASlide22
In the Lac operon, if lactose is not present what happens to the operon?
The Lac operon turns offSlide23
In the Lac operon, if lactose is present what happens to the operon?
The Lac operon turns onSlide24
These determine factors like presence of wings or legs
miRNA
Homeobox
Genes
Operator
Promoter