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

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

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

4. Gene Regulation When a Gene is Expressed: When a Gene is Silent:
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 Present lac 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