Gene Regulation Lac Operon

Eukaryotes use four primary ways to control the expression of genes. Transcriptional control – selection of genes to be transcribed and the rate of transcription Posttranscriptional control – processing of mRNA and the rate at which mRNA leaves the nucleus. Translational control – how long mRNA remains in the cytoplasm Posttranslational control – additional processing that proteins require to be functional or through feedback inhibition.

Oncogenes Genes that are responsible for signaling cells to divide - called proto-oncogenes When damaged cause uncontrolled cell division Carcinogen – Agents that cause cancer (mutations) – include radiation, cigarette smoke, and viruses

Normal Cells: Controlled growth Contact inhibition One organized layer Differentiated cells Cancer Cells: Uncontrolled growth No contact inhibition Disorganized, multilayered Nondifferentiated cells Abnormal nuclei

Mutagens Spontaneous – Alkylation – Oxidation – Etc Radiation – UV – Gamma, Beta, Alpha – Etc Chemical – Base analogue – Intercalating agents – Etc

Mutations

Gene Regulation in Prokaryotes In prokaryotes, genes must also be turned on and off. If genes are always expressed, then much energy is wasted. The organism will quickly become lethargic and very tired. An Operon consists of: – structural genes – promoter – Operator – Regulatory genes – Repressor and activator proteins

Repressible Operon - trp repressible operon is ON by default. regulatory genes produce inactive repressors. end product of the pathway, tryptophan, interacts with the inactive repressor (acting as a co-repressor), and causes a conformational change in the repressor. The active repressor is now able to bond to the operator and switch off transcription. Typical of anabolic pathways 02.html 02.html

Inducible Operon - lac Negative Regulation Regulatory gene produces repressor Repressor is bound to the Operator Allolactose will bond to repressor protein Repressor will be removed Operator RNA polymerase can transcribe 3/ html 3/ html mov mov

Lactose metabolism in E. coli 1.Transport lactose into the cell 2.Break down lactose into glucose and galactose galactoseglucose lactose Galactoside permease E. Coli cell

Lactose metabolism in E. coli The enzyme Beta-galactosidase breaks down lactose into glucose and galactose + Beta-galactosidase

Lac Operon Genes Operon: a group of genes that are commonly regulated and transcribed into mRNA Name of the GeneProtein Product of the Gene Lac I GeneProduces a Repressor Protein Lac Z GeneProduces Beta-Galactosidase Lac Y GeneProduces Galactoside Permease Lac A GeneProduces Transacetylase

Role of lactose Lactose is called an inducer molecule because it signals the production of: (a)Beta-galactosidase: the enzyme that cleaves lactose into glucose and galactose (b)Galactoside permease: the transport protein that allows lactose to enter a cell (c)Transacetylase: don’t worry about this one