Gene Regulation

2. Gene Regulation Complied by Siti Sarah Jumali Room 14, level 3 ext2123

3. Overall process of transcription and translation

4. Gene Expression An individual’s trillions of body cells all come from one cell (zygote). In differentiation the cells become different tissues (skin, muscle, organ) Certain cells will “turn on” or activate only the genes they need. This is called gene expression.

5. Factors that Affect Gene Expression The internal and external environment of a cell can influence which genes are “turned on”. Ex: - Hormones can “tell” a cell to activate a specific gene. - Outside temperature changes fur color in rabbits.

6. Regulation of bacterial expression Most microbial metabolic reactions require enzymes • Some enzymes are needed in large amount throughout the bacterial life as a living demand i.epyruvatedehydrogenasein glycolysis • In other cases, the enzyme were only needed in certain amount. This is when the operon system comes into play

7. Gene Expression Mechanism

8. Gene Regulation • How can genes be turned off and on? • Examples from E. coli • Inducer – example is lactose (lacoperon), pg 187 of (Black, J., 2005) • Repressor – argenine (argoperon), pg 187-188 of (Black, J., 2005)

9. Terminologies • Promoter – region of DNA where RNA polymerase initiate transcription • Operator – acts as the traffic light that instructs the structural genes which are going to be transcribed • Operon – consists of operator, promoter and three structural genes

10. The operon model of expression • Describes the regulation of protein expression • Genes that determine the surface of protein is known as structural genes • In lacoperon, there are 2 short DNA segment known as promoter and operator

11. Lac Operon of E. coli

12. Lac Operon

13. Induction on Gene Expression • Turns on the transcription of a gene • The substance involve is known as inducer • The enzymes which are synthesized in the presence of inducers are termed inducible enzymes • Eg. The enzyme β-galactosidase that splits lactose into glucose and galactose for E. coli.

14. Induction - Lac operon

15. Repression of Gene Expression • Inhibits gene expression and decreases enzyme synthesis • Prevent overabundance of and end product of a metabolic pathway • The protein used to decrease the rate of production is known as repressor • It has the ability to block transcription of an operon/RNA polymerase

16. Repression - Trpoperon

17. Regulatory proteins have two binding sites • One for a small effector molecule • The other for DNA

19. RNA pol cannot access the promoter Constitutive expression Therefore no allolactose The lacoperon is now repressed

20. Translation The lacoperon is now induced The conformation of the repressor is now altered Repressor can no longer bind to operator Some gets converted to allolactose

21. Repressor does not completely inhibit transcription So very small amounts of the enzymes are made The cycle of lac operon induction and repression

22. Example of positive control When cAMP binds to CAP, complex binds to CAP site near lac promoter Resulting bend in DNA enhances RNA polymerase binding which increases transcription

23. When both lactose and glucose are high, the lacoperon is shut off Glucose uptake causes cAMP levels to drop CAP does not activate transcription Bacterium uses one sugar at a time, glucose When lactose is high and glucose is low, the lacoperon is turned on Allolactose levels rise and prevent lac repressor from binding to operator CAP is bound to the CAP site Bacterium uses lactose When lactose is low and glucose is high or low, the lacoperon is shut off Under low lactose conditions, lac repressor prevents transcription of lacoperon

26. TazkirahRamadhan… “Dari Ma’qil bin YasardariNabi saw., beliaubersabda: Sesungguhnyaditusuknyakepalasalahseorangdiantarakamudenganjarumbesiitulebihbaikdaripadaiamenyentuhwanita yang tidakhalalbaginya.”(HR. ThabranidanBaihaqi)