Bio study guide IIIReading: 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 expressiona. The differences in phenotype are due to differences in gene expression partly because of evolution and the environments that we`re exposed tob. 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 expressiona. 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 occursa. Operator – a segment of DNA acting as a single “on-off” switch that can control a whole cluster of functionally related genes all at once; controls the access of RNA polymerase to the genes.b. Operon – the operator, promoter, and genes they control; the entire stretch of DNA required for enzyme production for the tryptophan pathwayc. Repressors –[protein product of a regulatory gene] switches off the operon by binding to the operator and blocking attachment of RNA polymerase to the promoter, preventing transcription of the genes; allosteric with two shapes: active and inactivei. 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 proteinto switch an operon offd. Induced – stimulates operons in order to get them from inactive to active state; turns 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 geneii. Regulatory gene codes for repressor that binds to operator region at start of coding regioniii. ‘signal molecule’ interacts with repressor to switch on or off1. Signal molecule is co-repressor in an anabolic system-final product turnsoff gene2. Signal is inducer in a catabolic gene-substrate turns on gene6) Know that gene expression in eukaryotes can be controlled at multiple stages during transcription and translationa. It can be controlled at many different stages:i. Chromatin modification (DNA packaging)ii. Transcription, RNA modification, RNA transport, translationiii. Post translation – protein modification, degradation, transport7) Be able to explain two ways in which modification of histone structure can affect transcription (acetylation and methylation)a. Histone acetylationi. Histones can have acetyl groups attached that repel one another, therefore causing loose chromatin structure and further allowing transcription to take placeb. Histone methylationi. Methyl groups attached prevent transcription by shutting down DNA at certain points8) Know that enhancers and transcription factors can affect transcriptiona. 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 cellsi. 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 domainsb. Activation domainsi. 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 – to initiate transcription, eukaryotic RNA polymerase requires the assistance of transcription factors.i. Protein to protein interactions are crucial to the initiation of transcriptionii. 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 transcriptiona. The interaction of general transcription factors and RNA polymerase II with a promoter leads to a low rate of initiationi. 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 transcriptiona. 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 mRNAa. MicroRNA (aka MiRNA) can bind to complementary sequences in mRNA molecules and affects it by either degrading it or blocking its translation.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
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