Bio study guide III Reading 18 1 18 3 review chapter 11 1 1 Be able to explain what gene expression means transcription and translation of genes a Gene expression based on what your body and environment needs a gene may be expressed or not expressed ie say you cut open your toe well your body won t turn on the gene for a new toe it will turn on the gene for making a new skin cell to replace the old and damaged ones in the hurt toe b Transcription i The first part of making a new protein mRNA is created this way in order to get the genetic sequence needed to make a new necessary protein ii Contains a transcription unit and a promoter promoter site where RNA polymerase can bind to DNA and begin transcription c Translation i Once the mRNA is made in transcription the cell can then translate it and make a polypeptide chain that will make up the necessary protein start and stop codons are necessary so that the cell knows where to start and stop during translation 2 Be able to explain that the differences in phenotype structure and function of cells with identical genomes is due to differences in gene expression a The differences in phenotype are due to differences in gene expression partly because of evolution and the environments that we re exposed to b Humans may be of the same species and family but because we re in different environments and have a whole range of various genes that we contain we are therefore different in phenotypes 3 Be able to explain that cell differentiation is largely a result of expression a This has to do with gene expression and determination b If a gene needs to be expressed then a cell will go through determination in order to differentiate into a cell type that has that gene expressed 4 Be able to explain that gene expression can either be induced or repressed and the situations in which that occurs a segment of DNA acting as a single on off switch that can control a whole a Operator cluster of functionally related genes all at once controls the access of RNA polymerase to the genes required for enzyme production for the tryptophan pathway to the operator and blocking attachment of RNA polymerase to the promoter preventing transcription of the genes allosteric with two shapes active and inactive the operator promoter and genes they control the entire stretch of DNA protein product of a regulatory gene switches off the operon by binding c Repressors b Operon i Gene expression is repressed when there s too much of something being made ie tryptophan present repressor active operon off therefore tryptophan acts as a Corepressor 1 Corepressor a small molecule that cooperates with a repressor protein to switch an operon off d stimulates operons in order to get them from inactive to active state turns Induced them on ie allolactose is an inducer that induces the lac operon i Gene expression is induced when not enough of something is being made lactose present repressor inactive operon on 5 Be able to explain the control of transcription in prokaryotes the binding of activators or repressors to special sites on the DNA a Three main common features i Separate coding region for regulatory gene ii Regulatory gene codes for repressor that binds to operator region at start of coding region signal molecule interacts with repressor to switch on or off iii 1 Signal molecule is co repressor in an anabolic system final product turns off gene 2 Signal is inducer in a catabolic gene substrate turns on gene 6 Know that gene expression in eukaryotes can be controlled at multiple stages during transcription and translation a It can be controlled at many different stages i Chromatin modification DNA packaging ii Transcription RNA modification RNA transport translation iii Post translation protein modification degradation transport 7 Be able to explain two ways in which modification of histone structure can affect transcription acetylation and methylation a Histone acetylation b Histone methylation points i Histones can have acetyl groups attached that repel one another therefore causing loose chromatin structure and further allowing transcription to take place i Methyl groups attached prevent transcription by shutting down DNA at certain 8 Know that enhancers and transcription factors can affect transcription a Enhancers distal control elements that are located at different locations upstream or downstream of a gene and each are active at different times in different types of cells i The rate of gene expression can be strongly increased or decreased by the binding of specific transcription factors either activators or repressors to the control elements of enhancers 1 Transcription activators have two main parts a DNA binding domains b Activation domains i Activation domains bind to other regulatory proteins of transcription resulting in a series of protein to protein interactions and therefore starting transcription of a given gene b Transcription factors assistance of transcription factors to initiate transcription eukaryotic RNA polymerase requires the i Protein to protein interactions are crucial to the initiation of transcription ii Only when the complete initiation complex has assembled can the polymerase begin to move along the DNA template strand 9 Know that enhancers and transcription factors can result in cell specific transcription a The interaction of general transcription factors and RNA polymerase II with a promoter leads to a low rate of initiation i So enhancers and transcription factors can result in cell specific transcription because faster rates of transcription depend on interactions btwn control elements called specific transcription factors 10 Know that RNA modification can affect the product of transcription a RNA modification can affect the product of transcription because of operons and whether or not it s being repressed or induced 11 Be able to explain how non coding RNA such as microRNA can affect mRNA a MicroRNA aka MiRNA affects it by either degrading it or blocking its translation can bind to complementary sequences in mRNA molecules and b Researchers discovered that injecting double stranded RNA molecules into a cell somehow turned off expression of a gene with the same sequence as the RNA a phenomenon called RNA interference RNAi
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