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?
Gene Expression • Genes 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.
Gene Regulation How Does A Cell Know? Which Gene To Express & Which Gene Should Stay Silent?
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-cellularorganism.
Gene Regulation • When a Gene is Expressed: • It is active and is Transcribedinto mRNA • When a Gene is Silent: • It is in active and is Not Transcribed
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: codesfor the repressor • Promoter: area on the DNA to which the RNA polymerase attaches to begin transcription
Vocabulary • Operator: area of the DNA to which the repressor binds; “on/off” switch • Structural genes: codefor enzymes which leads to a product
Gene Regulation • Expression Regulated By • Promoters • RNA Polymerase Binding Sites • Certain DNA Base Pair Sequences • Start&StopBase Pair Sequences • Regulatory Sites • DNA Binding Proteins • Regulate Transcription
Prokaryote Gene Regulation: • What is an Operon? • Group of Genes That Operate Together • For Example: • E. coliferments (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 thelacOperon(lactoseOperon)
Operons • Operon: made of three parts • Operator • Promoter • Group of genes • located together which express proteins for a similar function.
Two type of operons • Inducible • Example: lacoperon • Lac = lactose • Normally off but can be activated • Repressible • Example: trpoperon • Trp = tryptophan • Normally on but can be inhibited
Gene Regulation: lac Operon Thelac 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: • Transport Lactose Across Cell Membrane • Separate The Two Sugars
Gene Regulation: lacOperon Each Task Requires A Specific Protein but 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: lacOperon ADDLACTOSE = Lactose
Gene Regulation: lac Operon Key Concept: Thelac GenesAre: Turned OffBy Repressors And Turned OnBy The Presence Of Lactose
lac Gene Expression • Operon Has 2 Regulatory Regions • Promoter (RNA Polymerase Binding) • Operator (O region) Bound To A lacRepressor
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 Presentlac Repressor Is Released From O Region • Allows Transcription of All Three Genes
Regulation Can Be: • Based On Repressors • Based On Enhancers • Regulated At Protein Synthesis
Eukaryotic Gene Regulation Operons Usually NOT 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 • 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 Promoters Enhancer Sequences • Series of Short DNA Sequences • Many Types Enormous Number Of Proteins Can Bind To Enhancer Sequences • Makes Eukaryote Enhancement Very Complex
Eukaryotic Promotors • 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.