Lac operon Tryptophan operon 1) Inducible gene complex. 2) Catabolic system (converts lactose into glucose). 3) Contains 3 structural Genes. 4) Produces 3 inducible enzymes. 5) Repressor protein is active. 6) High lactose turn transcription ON, in low glucose level. 7) Lactose act as inducer. 8) Has 2 types of gene regulation: - Negative & positive control. - Negative & positive control. 9) Usually OFF, active under certain condition. 10) cAMP is necessary for CAP to switch transcription ON. 1) Repressible gene complex. 2) Anabolic system (synthesizes tryptophan). 3) Contains 5 structural Genes. 4) Produces 5 repressible enzymes. 5) Repressor protein is inactive. 6) High tryptophan turn transcription OFF. 7) Tryptophan act as co-repressor. 8) Has one type of gene regulation: - Negative control. - Negative control. 9) Usually ON, inactive at high level of tryptophan 10) cAMP is not necessary Enumerate the differences between Lactose & tryptophan operons?Enumerate the differences between Lactose & tryptophan operons?

General features: In Eukaryotic Cells, it is more complicated and multifaceted. 1) The changes in environment; turn a set of genes ON or OFF (viral infection & heat shock). 2) Tissue specific regulation; specialization and organization of the cells in organs require activation of some genes & inactivation of others. 3) Operons are not present in eukaryotic cells. 4) Specific regulatory sequence; for each gene. 5) House-keeping enzymes; are encoded by constitutive genes. 6) Temporal regulation mechanism, some genes are active only during certain period of life (inducible). Gene Regulation In Eukaryotic Cells Gene Regulation In Eukaryotic Cells

1) DNA or Chromosomal organization. 2) Gene transcription level. 3) Post-transcription level. 4) Translation control. 5) Post-translation control. Levels of Gene Expression Control In Eukaryotic Cells

1) Formation multiple copies of genes. e.g.: rRNA & tRNA e.g.: rRNA & tRNA (the cell contains 150 – 450 transcription units). (the cell contains 150 – 450 transcription units). 2) Gene amplification (self –replication of some genes to increase their product). to increase their product). 2) Gene inactivation by: a) Change chromatin structure. a) Change chromatin structure. formation a compact mass of inactive heterochromatin. formation a compact mass of inactive heterochromatin. e.g. x- chromosome form Barr body. e.g. x- chromosome form Barr body. b) DNA –methylation. b) DNA –methylation. - addition of methyl group to DNA-cytosine - addition of methyl group to DNA-cytosine methyl cytosine. methyl cytosine. - Methy cytosine + specific protein - Methy cytosine + specific protein methyl cytosine protein complex methyl cytosine protein complex. a) Gene expression control at level of DNA organization Blockstranscription Methyl cytosine Specific protein

Control of the rate of transcription depends on: Control of the rate of transcription depends on: 1) Efficiency of promoter 1) Efficiency of promoter 2) Enhancer 2) Enhancer 3) Regulatory protein 3) Regulatory protein (transcription requires multiple regulatory proteins called general transcription machinery or regulatory protein complex). (transcription requires multiple regulatory proteins called general transcription machinery or regulatory protein complex). b) Gene expression control at Transcription level Promoter Transcription initiation site TATA -boxUPEsEnhancer About 100 base pairs 30 base pairs About several thousands of base pairs DNA

Composition: Composition: 1) TATA –box : Binding site of RNA –polymerase. Binding site of RNA –polymerase. Formed of T & A. Formed of T & A. About 30 base pairs in upstream from About 30 base pairs in upstream from transcription initiation site. transcription initiation site. 2) UPEs (upstream promoter elements): Each one about 8 – 12 base pairs Each one about 8 – 12 base pairs About 100 base pairs in upstream from initiation site. About 100 base pairs in upstream from initiation site. Activity of promoter depends on the number & type of UPEs. Activity of promoter depends on the number & type of UPEs. Weak promoter contains few UPEs. Weak promoter contains few UPEs. Strong promoter contains several UPEs. Strong promoter contains several UPEs. UPEs are required for accurate & efficient initiation of mRNA – synthesis. UPEs are required for accurate & efficient initiation of mRNA – synthesis. 1) Promoter

DNA –sequence Increase rate of Gene transcription, when it interacts with transcription machinery complex in presence of the activator protein May be activator or repressor protein. Transcription requires multiple regulatory proteins, R. Protein complex. Regulatory protein complex binds to TATA –box to facilitate the binding of RNA polymerase, that results in formation of transcription machinery complex. Have 2 functional domains; one binds to Enhancer & the other connects the transcription machinery complex. Increase rate of transcription & mRNA synthesis. 2) Enhancer 3) Regulatory protein 4) Activator protein

2)No transcription, although RNA-polymerase & Transcription M.C. are bound to TATA-box. ( Transcription is very low or not at all ) Initiation site TATA –box Regulatory protein complex (multiple proteins) 1) R.P. complex is required for binding of RNA polymerase enhancer RNA-polymerase Transcription machinery complex 3) Activator protein facilitates interaction between Enhancer & T.M.C. to accelerate rate of transcription. DNA –loop allows interaction between: - Activator protein, - Enhancer - Transcription.M.C. DNA activator Transcription ON enhancer

1) Proteolytic process: Pepsinogen (inactive) Pepsin (active) Pepsinogen (inactive) Pepsin (active) 2) Selective degradation: To maintain a suitable concentration of protein within the cell and removal the unuseful parts. To maintain a suitable concentration of protein within the cell and removal the unuseful parts. 3) Chemical modification: removal or addition functional group to activate or inactivate some enzymes, such as phosphate group. removal or addition functional group to activate or inactivate some enzymes, such as phosphate group. Proteolytic enzymes Gene Expression at Post-translation level