2. Four of the many different types of human cells: They all share the same genome. What makes them different?

3.  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.

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

5. ◦ 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.

6.  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

8.  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

9.  Operator: area of the DNA to which the repressor binds; “on/off” switch  Structural genes: code for enzymes which leads to a product

10.  Expression Regulated By 1.Promoters  RNA Polymerase Binding Sites  Certain DNA Base Pair Sequences 2.Start&StopBase Pair Sequences 2.Start & Stop Base Pair Sequences 3.Regulatory Sites  DNA Binding Proteins  Regulate Transcription

12.  What is an ?  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  3 Genes Turned On & Off Together. This is known as the lac Operon (lac tose Operon)

13.  Operon: made of three parts 1.Operator 2.Promoter 3.Group of genes  located together which express proteins for a similar function.

14. 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

15. The lac Operon ◦ Regulates Lactose Metabolism ◦ It Turns On Only When Lactose Is Present & Glucose is Absent ◦ 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 Membrane 2.Separate The Two Sugars

16. 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 Present But Lactose Is Present Genes Coding For Proteins Expressed Only When There Is No Glucose Present But Lactose Is Present

18. = Lactose ADDLACTOSE ADD LACTOSE

20. Key Concept Key Concept : The lac Genes Are: Turned Off By Repressors And And Turned On By The Presence Of Lactose

21.  Operon Has 2 Regulatory Regions 1.Promoter (RNA Polymerase Binding) 2.Operator (O region) Bound To A lac Repressor

22.  lac Repressor ◦ When Bound To O Region : Prevents Binding of RNA Polymerase To Promoter ◦ Turns The Operon “OFF”

23.  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

25. 1. Based On Repressors 2. Based On Enhancers 3. Regulated At Protein Synthesis

26. 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

28.  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

29. Enhancer Sequences ◦ Series of Short DNA Sequences ◦ Many Types Enormous Number Of Proteins Can Bind To Enhancer Sequences ◦ Makes Eukaryote Enhancement Very Complex

30.  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.