How and Why Genes Are Regulated
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Transcript of How and Why Genes Are Regulated
Four of the many different types of human cells:
They all share the same genome.What makes them different?
How and Why Genes Are Regulated
Gene ExpressionGenes are expressed as traits
Traits are proteins or result from reactions which are regulated by proteins, such as enzymes.
Genes are expressed through protein synthesis.
How Does A Cell Know? Which Gene To Express
& Which Gene Should Stay
Silent?
Gene Regulation
Patterns of Gene Expression in Differentiated Cells◦In cellular differentiation:
Certain genes are turned on and off. Cells become specialized in structure and function.
◦In gene expression: A gene is turned on and transcribed into RNA. Information flows from genes to proteins, genotype to
phenotype.◦ The regulation of gene expression plays a central role in
development from a zygote to a multi-cellular organism.
When a Gene is Expressed:◦It is active and is Transcribed into mRNA
When a Gene is Silent:◦It is in active and is Not Transcribed
Gene Regulation
Patterns of Gene Expression in Specialized Human Cells
Vocabulary RNA polymerase: RNA polymerase (RNAP or RNApol) is an enzyme that produces RNA.
Repressor: inhibits transcription of structural genes by binding to the operator
Regulatory gene: codes for the repressor
Promoter: area on the DNA to which the RNA polymerase attaches to begin transcription
VocabularyOperator: area of the DNA to which the repressor binds; “on/off” switch
Structural genes: code for enzymes which leads to a product
Expression Regulated By1. Promoters RNA Polymerase Binding Sites Certain DNA Base Pair Sequences
2. Start & Stop Base Pair Sequences
3. Regulatory Sites DNA Binding Proteins Regulate Transcription
Gene Regulation
Gene Regulation
What is an Operon? Group of Genes That Operate Together
For Example:◦E. coli ferments (digests) lactose To 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)
Prokaryote Gene Regulation:
OperonsOperon: made of three parts1. Operator2. Promoter3. Group of genes
located together which express proteins for a similar function.
1. Inducible◦ Example: lac operon Lac = lactose
◦ Normally off but can be activated
2. Repressible◦ Example: trp operon Trp = tryptophan
◦ Normally on but can be inhibited
Two type of operons
The lac Operon◦ Regulates Lactose Metabolism◦ It Turns On Only When Lactose Is
Present & Glucose is Absent.Lactose is a Disaccharide
◦ A Combination of Galactose & Glucose To Ferment Lactose E. coli Must:
1. Transport Lactose Across Cell Membrane2. Separate The Two Sugars
Gene Regulation: lac Operon
Each Task Requires A Specific Proteinbut
Proteins Not Needed If Glucose Present (why waste energy if you already have
food?)so
Genes Coding For Proteins Expressed Only When There Is No Glucose Present
But Lactose Is Present
Gene Regulation: lac Operon
Gene Regulation: lac Operon
Gene Regulation: lac Operon
= Lactose
ADD LACTOSE
Gene Regulation: lac Operon
Key Concept:The lac Genes Are:
Turned Off By Repressors And
Turned On By The Presence Of Lactose
Gene Regulation: lac Operon
Operon Has 2 Regulatory Regions1. Promoter
(RNA Polymerase Binding)
2. Operator (O region) Bound To A lac Repressor
lac Gene Expression
lac Repressor◦ When Bound To O
Region : Prevents Binding of RNA Polymerase To Promoter
◦ Turns The Operon “OFF”
lac Gene Expression
lac Repressor Also Binds To Lactose◦ Higher Affinity For
Lactose When Lactose
Present lac Repressor Is Released From O Region◦ Allows Transcription of
All Three Genes
lac Gene Expression
Compare and Contrast
1. Based On Repressors2. Based On Enhancers3. Regulated At Protein
Synthesis
Regulation Can Be:
Operons UsuallyNOT Found In Eukaryotes
Key Concept:Most Eukaryotic Genes Are Controlled Individually And Have Regulatory Sequences That Are Much More Complex Than Prokaryotic Gene Regulation
Eukaryotic Gene Regulation
Eukaryotic Gene Regulation
TATA Box◦About 30 Base Pairs Long◦Found Before Most Genes◦Positions RNA Polymerase◦Usually TATATA or TATAAA◦Promoters Usually Occur Just Before The TATA Box
Eukaryotic Gene Regulation
Enhancer Sequences◦ Series of Short DNA Sequences◦ Many Types
Enormous Number Of Proteins Can Bind To Enhancer Sequences
◦ Makes Eukaryote Enhancement Very Complex
Eukaryotic Promoters
Some Enhance Transcription By Opening Up Packed Chromatin
Others Attract RNA Polymerase Some Block Access To Genes Key To Cell Specialization
◦ All Cells Have Same Chromosomes◦ Some Liver, Skin, Muscle, etc.
Eukaryotic Promotors
The End