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Transcript
Regulation of Gene Expression Questions? How can cells with different functions have the exact same DNA in their nucleus? How does the body use the exact same set of instructions to make different structures? Core Concepts • DNA triplets code for how many amino acids? (Codons) • Amino acids link together and form polypeptides • Genes code for polypeptides that control things like? • Gene expression can happen in 2 ways, positive and negative • Very small percentage of human genome codes for protein Prokaryotic VS Eukaryotic Gene Expression Differences in the Regulation of Gene Expression of Prokaryotic and Eukaryotic Organisms Prokaryotic organisms Eukaryotic organisms Lack nucleus Contain nucleus DNA is found in the cytoplasm DNA is confined to the nuclear compartment RNA transcription and protein formation occur almost simultaneously RNA transcription occurs prior to protein formation, and it takes place in the nucleus. Translation of RNA to protein occurs in the cytoplasm. Gene expression is regulated primarily at the transcriptional level Gene expression is regulated at many levels (epigenetic, transcriptional, nuclear shuttling, post-transcriptional, translational, and posttranslational) Gene Expression in Prokaryotes • Transcriptional Control: the cell can speed up or slow down the transcription of mRNA from the gene that codes for the polypeptide • Post-transcriptional Control: the cell may transcribe the mRNA but break it down before translation. It can also modify the poly-A tail. WHY? • Post-translational Control: after synthesizing the polypeptide the cell can modify it chemically or vary the rate at whish the polypeptide becomes a functional protein OPERONS • Stretch of DNA that contains one or more genes involved in a metabolic pathway along with a regulatory sequence called an operator OPERATOR • DNA sequence located between promoter sequences and gene sequences that govern whether RNA polymerase can bind to the promoter sequence to begin transcription REPRESSOR • Protein that binds to the operator to make it impossible for the RNA polymerase to bind to the promoter, thus preventing genes from being transcribed INDUCER • Substance such as lactose molecule that stops the action of the repressor, allowing RNA polymerase to bind to the promoter sequence and begin transcription lac Operon- E-coli Bacteria • https:/ /www. youtub e.com/ watch? v=oBw txdI1zv k Negative Gene Regulation in the lac Operon • Uses a REPRESSOR (protein) which binds to the operator region and doesn’t allow for RNA polymerase to bind to the promoter, resulting in the lac operon not being transcribed. Positive Gene Regulation in the lac Operon • Uses ACTIVATORS (molecule that promotes action of enzymes), specifically Catabolic Activator Protein (CAP), that stimulates gene expression by binding to a cAMP molecule and then to s site near the Plac promoter. • This action allows RNA polymerase to bind to the promoter easily and speeds up the rate at which lac genes are transcribed. Negative Gene Expression: -Like a key for a car, your turning it on or off (turning off transcription/translation). Positive Gene Expression: -Like the gas pedal and brake, accelerating and slowing it down (accelerating and slowing down transcription/translation). Gene Expression in Eukaryotes https://www.youtube.com/watch?v=KKR28Y_L4CA • Pre-transcriptional control: the cell controls the extent to which DNA is exposed to transcription enzymes, regulating DNA’s availability for transcription. • Transcriptional control: the cell controls whether or not exposed DNA is transcribed into Pre-mRNA. • Post-transcriptional control: the cell controls the rate of processing of premRNA, but then controls. • Translational control: the cell manufactures the mRNA, but then controls its transport to ribosomes in the cytoplasm • Post-translational control: the cell manufactures the polypeptide but then modifies it chemically or varies the rate at which it becomes a functional protein. It may also break down the polypeptide before it becomes functional Activity: • Choose a positive or negative example of gene expression in Eukaryotes, then draw and label it.
