Gene Regulation Prokaryotes And Eukaryotes PDF

Gene Regulation Prokaryotes and Eukaryotes  Gene Regulation Control of the level of gene expression. Determines whether a gene is active or inactive Determines the level of activity, and amount of protein available in the cell. Constitutive genes: genes that are constantl...

Gene Regulation Prokaryotes and Eukaryotes  Gene Regulation Control of the level of gene expression. Determines whether a gene is active or inactive Determines the level of activity, and amount of protein available in the cell. Constitutive genes: genes that are constantly being expressed because Prokaryotic Gene Expression In prokaryotes, genes are turned on and off. If genes are always expressed, then much energy is wasted. The organism will quickly become lethargic and very tired. Occurs at three different levels: – During transcription (most common, and usually during initiation) – During translation – After the protein is made  Many genes are clustered together in a region that is under the control of a single promoter. These are called operons. Genes that are involved in the same metabolic pathways are often in the operon. They are transcribed together as one continuous mRNA strand – polycistronic mRNA. Individual proteins are made from that mRNA.  Components of operons Coding region: contains the genes to be expressed. Regulatory region: contains the promoter. Operator: DNA sequence that a protein binds to in order to inhibit transcription initiation. Repressor: Protein that binds to DNA and inhibits transcription initiation. Activator: Protein that determines how fast the genes are transcribed. Repressible Operon  Repressible Operon - trp repressible operon is ON by default. regulatory genes produce inactive repressors. Allosteric Regulation: 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 bind to the operator and switch off  Co-Repressor and Repressor A co-repressor is a molecule that can bind to the repressor and make it bind to the operator tightly, which decreases transcription A repressor that binds with a co- repressor is termed an inactive repressor One type of inactive repressor is the trp repressor  Lac operon Steps Regulatory gene produces repressor Repressor is a protein that binds to the Operator (a sequence of DNA similar to TTATTA Box) When repressor protein is bound RNA Polymerase can’t transcribe. Allosteric Regulation of Repressor: lactose binds to repressor protein changing its shape. It can no longer bind to Operator sequence. RNA polymerase can transcribe  lac operon Positive Regulation Glucose Present: Lots of ATP – lac operon should be turned off. Low glucose: Low ATP = high cAMP cAMP is as hunger signal made when glucose levels are low cAMP binds to a third protein called CRP = cAMP/CRP complex When cAMP binds onto CRP, the shape makes it bind to DNA & promote transcription CRP binds to Promoter enhancing affinity for RNA Polymerase High ATP = low cAMP so CRP is not active  Eukaryotic Gene Expression Transcriptional control – selection of genes to be transcribed and the rate of transcription – carried out by Transcription Factors (TFs): small proteins that bind to Promoter regions of DNA. They act as signals telling the RNA Polymerase to stop copying. – Funny names like Fos, Jun, myb, myc, ets 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. https://www.youtube.com/watc h?v=h_1QLdtF8d0