Chapter 12 - Gene Regulation

Mrna these mrnas are called riboswitches because they

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Unformatted text preview: As are called riboswitches because they undergo conformational change and can suppress gene expression Riboswitches allow bacteria to regulate gene expression in response to some metabolites Control of Gene Expression in Eukaryotes o o o o o o o o o o Cells of a complex eukaryote exist in many differentiated states But differentiated cells retain a full set of genes not the presence of absence of genes is important, but how those genes are used is what matters Sheep experiment: nucleus of Sheep B was extracted and put in cell of Sheep A created clone of Sheep B therefore cells contain all the genetic information required for the differentiation of other types of cells Genes are turned on and off as a result of interaction with regulatory proteins Some proteins (example: Glycolysis enzymes) are produced in virtually all types of cells Some proteins are unique to a certain cell type Regulation of gene expression occurs on 3 levels: transcriptional level control, processing level control and translational level control Transcriptional level control determines whether a gene can be transcribed and how often Processing level control determines the path by which pre-mRNA is processed Translational level control determines whether a particular mRNA is translated, how often and for how long Transcriptional Level Control o o o o o o o Differential transcription is the most important mechanism by which eukaryotic cells determine which proteins are synthesized Transcription factors are proteins that either act as transcription activators or transcription inhibitors a single gene can be controlled by different regulatory proteins A single DNA-binding protein may control the expression of many different genes Control of gene expression is complex and influenced by a wide variety of factors affinity of transcription factors for particular DNA sequences ability of transcritption factors to interact with eachother cells exposed to different stimuli respond by synthesizing different transcription factors 2 Transcription Factors and Phenotype o o o Embryonic stem (ES) cells are pluripotent capable of differentiating into all of the different types of cells Transcription factors normally produced by ES cells were introduced and shown to reprogram fibroblast cells into cells that acted like pluripotent ES cells just 4 needed Oct4, Sox2, Myc and Klf4 Reprogramming occurs gradually as cells divide original transcription factors shut off as cells endogenous pluripotency genes are turned on, which is accompanied by reorganization of chromatin Transcription Factors o o o Transcription factors contain DNA binding domain binds specific base pair sequences And an activation domain regulates transcription by interacting with different proteins DNA binding domains can be grouped into broad classes by motifs (transcription factor motifs) most motifs contain a segment that binds to the major groove of the DNA Transcription Factor Motifs o Motifs: helix-turn-helix (HTH), zinc-finger, helix-loop-helix (HLH), leucine zipper Helix-turn-Helix Motif o o o Simplest motif first found in prokaryotes Two alpha helices connected by a short extended chain of amino acids turn Amino acid side chains of recognition helix (the more Cterminal helix) play an important part in recognizing the specific DNA sequence to which the protein binds Zinc-Finger Motif o o The largest in ma...
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