Gene Expression Key points of 3 ways in which gene expression is controlled 4.0 / 5 based on 2 ratings ? BiologyDNA, genetics and evolutionA2/A-levelAQA Created by: clarenceofcydoniaCreated on: 17-03-13 15:10 Transcription Factors Switch genes on/off Interact with promoter sequence of DNA- either initiate or inhibit transcription They move from the cytoplasm to the nucleus Bind to specific promoter DNA sites (near start of target genes) Control expression by controlling rate of transcription Activators: increase rate of transcription, help RNA polymerase bind to promoter sequence and activate transcription Repressors: decrease rate of transcription, bind to start of target gene, prevents RNA polymerase from binding, stopping transcription 1 of 3 Oestrogen Mechanism: gene repressed by inhibitor (method for transcription factors) Lipid soluble hormone has small hydrophobic molecules Diffuses through plasma membrane of cells In cytoplasm- diffuses to nuclueus Binds to hormone receptor molecule on transcriptional factor Releases inhibitor molecule Switches on gene for transcription Occurs with plant hormones (auxins, gibberellin) in same way Oestrogen- lipid soluble mammalian hormone Small hydrophobic molecules- diffuse through plasma membranes of cells Once in cytoplasm, moves to nucleus Binds to type of oestrogen receptor molecule on the transcriptional factor Releases inhibitor molecule Switches on gene for transcription 2 of 3 siRNA Molecules are short, double stranded RNA molecules- interfere with the expression of specific genes Bases complementary to specific sections of target gene (and mRNA formed from it) Affects translation through RNA interference: mRNA molecules degraded by enzymes after translation Small sections of double stranded siRNA formed One strand combines with enzyme/ protein (RISC-RNA induced silencing complex) siRNA guides protein to mRNA molecule- pairs up bases with complementary ones on sections of mRNA molecule Enzyme now cuts mRNA into smaller sections mRNA can no longer be translated into a polypeptide The gene is blocked so is no longer expressed 3 of 3
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