1. GENE REGULATION

2. Virtually every cell in your body contains a complete set of genes Virtually every cell in your body contains a complete set of genes But they are not all turned on in every tissue But they are not all turned on in every tissue Each cell in your body expresses only a small subset of genes at any time Each cell in your body expresses only a small subset of genes at any time During development different cells express different sets of genes in a precisely regulated fashion During development different cells express different sets of genes in a precisely regulated fashion

3. GENE REGULATION Gene regulation occurs at the level of transcription or production of mRNA Gene regulation occurs at the level of transcription or production of mRNA A given cell transcribes only a specific set of genes and not others A given cell transcribes only a specific set of genes and not others Insulin is made by pancreatic cells Insulin is made by pancreatic cells

4. CENTRAL DOGMA Genetic information always goes from DNA to RNA to protein Genetic information always goes from DNA to RNA to protein Gene regulation has been well studied in E. coli Gene regulation has been well studied in E. coli When a bacterial cell encounters a potential food source it will manufacture the enzymes necessary to metabolize that food When a bacterial cell encounters a potential food source it will manufacture the enzymes necessary to metabolize that food

5. Gene Regulation In addition to sugars like glucose and lactose E. coli cells also require amino acids In addition to sugars like glucose and lactose E. coli cells also require amino acids One essential aa is tryptophan. One essential aa is tryptophan. When E. coli is swimming in tryptophan (milk & poultry) it will absorb the amino acids from the media When E. coli is swimming in tryptophan (milk & poultry) it will absorb the amino acids from the media When tryptophan is not present in the media then the cell must manufacture its’ own amino acids When tryptophan is not present in the media then the cell must manufacture its’ own amino acids

6. Trp Operon E. coli uses several proteins encoded by a cluster of 5 genes to manufacture the amino acid tryptophan E. coli uses several proteins encoded by a cluster of 5 genes to manufacture the amino acid tryptophan All 5 genes are transcribed together as a unit called an operon, which produces a single long piece of mRNA for all the genes All 5 genes are transcribed together as a unit called an operon, which produces a single long piece of mRNA for all the genes R Operon Regulatory Gene POEDC 5 Proteins B A L Inactive repressor (apo-repressor)

7. RNA polymerase binds to a promoter located at the beginning of the first gene and proceeds down the DNA transcribing the genes in sequence RNA polymerase binds to a promoter located at the beginning of the first gene and proceeds down the DNA transcribing the genes in sequence The tryptophane gene is turned on when there is no tryptophan in the media The tryptophane gene is turned on when there is no tryptophan in the media the trp gene is a repressible gene (Genes whose expression is turned off by the presence of some substance (co-repressor)) the trp gene is a repressible gene (Genes whose expression is turned off by the presence of some substance (co-repressor)) That is when the cell wants to make its’ own tryptophan That is when the cell wants to make its’ own tryptophan

8. Fig. 16.6

9. Tryptophan Operon Co-repressor -- tryptophan Co-repressor -- tryptophan Absence of tryptophan Absence of tryptophan Gene expression Gene expression R POEDC 5 Proteins B A L Inactive repressor (apo-repressor) Absence of Tryptophan R POEDC No trp mRNA B A L Presence of Tryptophan Inactive repressor (apo-repressor) Trp (co-repressor) Presence of tryptophan Presence of tryptophan Activates repressor Activates repressor No gene expression No gene expression Negative control Negative control

10. GENE REGULATION In addition to amino acids, E. coli cells also metabolize sugars in their environment In addition to amino acids, E. coli cells also metabolize sugars in their environment In 1959 Jacques Monod and Fracois Jacob looked at the ability of E. coli cells to digest the sugar lactose In 1959 Jacques Monod and Fracois Jacob looked at the ability of E. coli cells to digest the sugar lactose

11. GENE REGULATION In the presence of the sugar lactose, E. coli makes an enzyme called beta galactosidase In the presence of the sugar lactose, E. coli makes an enzyme called beta galactosidase Beta galactosidase breaks down the sugar lactose so the E. coli can digest it for food Beta galactosidase breaks down the sugar lactose so the E. coli can digest it for food It is the LAC Z gene in E coli that codes for the enzyme beta galactosidase It is the LAC Z gene in E coli that codes for the enzyme beta galactosidase

12. Lac Z Gene Lac Z is an inducible gene ( Genes whose expression is turned on by the presence of some substance) Lac Z is an inducible gene ( Genes whose expression is turned on by the presence of some substance) E. coli cells can not make the sugar lactose E. coli cells can not make the sugar lactose They can only have lactose when it is present in their environment They can only have lactose when it is present in their environment Then they turn on genes to break down lactose Then they turn on genes to break down lactose

13. GENE REGULATION The E. coli bacteria only needs beta galactosidase if there is lactose in the environment to digest The E. coli bacteria only needs beta galactosidase if there is lactose in the environment to digest There is no point in making the enzyme if there is no lactose sugar to break down There is no point in making the enzyme if there is no lactose sugar to break down It is the combination of the promoter and the DNA that regulate when a gene will be transcribed It is the combination of the promoter and the DNA that regulate when a gene will be transcribed

14. GENE REGULATION This combination of a promoter and a gene is called an OPERON This combination of a promoter and a gene is called an OPERON Operon is a cluster of genes encoding related enzymes that are regulated together Operon is a cluster of genes encoding related enzymes that are regulated together i Operon Regulatory Gene p oz y a DNA m-RNA  -Galactosidase Permease Transacetylase Protein

16. LAC Z GENE E. coli regulate the production of Beta Galactocidase by using a regulatory protein called a repressor E. coli regulate the production of Beta Galactocidase by using a regulatory protein called a repressor The repressor binds to the lac Z gene at a site between the promotor and the start of the coding sequence The repressor binds to the lac Z gene at a site between the promotor and the start of the coding sequence The site the repressor binds to is called the operator The site the repressor binds to is called the operator

18. LAC Z GENE Normally the repressor sits on the operator repressing transcription of the lac Z gene Normally the repressor sits on the operator repressing transcription of the lac Z gene In the presence of lactose the repressor binds to the sugar and this allows the polymerase to move down the lac Z gene In the presence of lactose the repressor binds to the sugar and this allows the polymerase to move down the lac Z gene i p o z y a No lac mRNA Absence of lactose Active i p o z y a  -Galactosidase PermeaseTransacetylase Presence of lactose Inactive

19. LAC Z GENE When there is no sugar left the repressor will return to its spot on the chromosome and stop the transcription of the lac Z gene When there is no sugar left the repressor will return to its spot on the chromosome and stop the transcription of the lac Z gene i p o z y a No lac mRNA Absence of lactose Active

21. Negative control (bound repressor inhibits transcription)

22. Catabolite Repression (Glucose Effect) Definition: Control of an operon by glucose Definition: Control of an operon by glucose + glucose - glucose Time (hr) Units of galactosidase + lactose Glucose added Catabolic operons Catabolic operons

23. Mechanism of Catabolite Repression c-AMP c-AMP CAP (CRP) protein CAP (CRP) protein CAP-cAMP complex CAP-cAMP complex Promoter activation Promoter activation Absence of glucose i po z y a Active  -Galactosidase PermeaseTransacetylase CAP Inactive ATP Adenyl cyclase c-AMP Maximum expression Positive control (bound activator facilitates trancription)

24. Mechanism of Catabolite Repression Glucose  :cAMP  Glucose  :cAMP  CAP (CRP) protein CAP (CRP) protein No CAP-cAMP complex No CAP-cAMP complex No Promoter activation No Promoter activation Presence of glucose i p o z y a Inactive ATP Adenyl cyclase CAP X  -Galactosidase PermeaseTransacetylase Low level expression

25. GENE REGULATION In eukaryotic organisms like ourselves there are several methods of regulating protein production In eukaryotic organisms like ourselves there are several methods of regulating protein production Most regulatory sequences are found upstream from the promoter Most regulatory sequences are found upstream from the promoter Genes are controlled by regulatory elements in the promoter region that act like on/off switches or dimmer switches Genes are controlled by regulatory elements in the promoter region that act like on/off switches or dimmer switches

26. GENE REGULATION Specific transcription factors bind to these regulatory elements and regulate transcription Specific transcription factors bind to these regulatory elements and regulate transcription Regulatory elements may be tissue specific and will activate their gene only in one kind of tissue Regulatory elements may be tissue specific and will activate their gene only in one kind of tissue Sometimes the expression of a gene requires the function of two or more different regulatory elements Sometimes the expression of a gene requires the function of two or more different regulatory elements