Chapter 12 DNA & RNA

1. Chapter 12DNA & RNA Section 12 – 5Gene Regulation

2. Objectives • How are lac genes turned off and on? • How are most eukaryotic genes controlled?

3. Gene Regulation How Does A Cell Know? Which Gene To Express & Which Gene Should Stay Silent?

4. Gene Regulation • When a Gene is Expressed: • It Is Transcribed Into mRNA • When a Gene is Silent: • It Is Not Transcribed

5. Gene Regulation • Expression Regulated By • Promoters • RNA Polymerase Binding Sites • Certain DNA Base Pair Sequences • Start & Stop Base Pair Sequences • Regulatory Sites • DNA Binding Proteins • Regulate Transcription

6. Gene Regulation

7. Gene Regulation: lac Operon • What is an Operon? • Group of Genes That Operate Together • For Example: • E. coli ferments 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

8. Gene Regulation: lac Operon 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: • Transport Lactose Across Cell Membrane • Separate The Two Sugars

9. Gene Regulation: lac Operon 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

10. Gene Regulation: lac Operon

11. Gene Regulation: lac Operon ADD LACTOSE = Lactose

12. Gene Regulation: lac Operon

13. Gene Regulation: lac Operon Key Concept: The lac Genes Are: Turned Off By Repressors And Turned On By The Presence Of Lactose

14. lac Gene Expression • Operon Has 2 Regulatory Regions • Promoter (RNA Polymerase Binding) • Operator (O region) Bound To A lac Repressor

15. lac Gene Expression • lac Repressor • When Bound To O Region : Prevents Binding of RNA Polymerase To Promoter • Turns The Operon “OFF”

16. 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

17. Regulation Can Be: • Based On Repressors • Based On Enhancers • Regulated At Protein Synthesis

18. 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

19. Eukaryotic Gene Regulation

20. 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

21. 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

22. 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.

23. Regulation & Development • hox Genes • Control Organ & Tissue Development In The Embryo • Mutations Lead To Major Changes • Drosophila With Legs In Place of Antennae

24. Regulation & Development

25. Regulation & Development hox Genes Present In All Eukaryotes • Shows Common Ancestry • Pax 6 hox gene • Controls eye growth in Drosophila, Mice & Man • Pax 6 from Mouse Placed In Knee Development Sequence Of Drosophila Developed Into Eye Tissue. Common Ancestor >600M Years Ago

26. Regulation & Development