Topic 22 - Gene Expression.docx

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Western University
Biochemistry 2280A
Chris Brandl

BIOCHEMISTRY Topic 22 November 6, 2012 Topic 22: Transcription and Gene Expression Gene Expression • Information is stored in DNA in the form of genes • Human genome ~25000 different protein encoding genes • In any one cell, ~5000 - 10000 are expressed at various levels • Expression is essential for growth and differentiation of all cells Control of Gene Expression • genes can be switched on/off depending on need • euks gene control more elaborate than prok  in euk: fertilized egg cells differentiate  differentiation achieved by changes in gene expression  cells make and accumulate different sets of RNA and protein so express diff genes  but all cells contain same genome • some proteins are common to all cells in multicellular organism  housekeeping proteins (ex. RNA polymerase, DNA repair enzymes, etc. ) • mass spectrometry can be used to detect presence of rare proteins in tiny amounts • monitor mRNA to study gene expression • gene expression can change in response to external signals  different cells may have different rxns to the same external signal Significance of Gene Expression • Many diseases are due to altered expression of one or more genes • Incorrect gene expression gives rise to disease BIOCHEMISTRY Topic 22 November 6, 2012 • By manipulating gene expression, we have the potential to prevent or reverse disease  Ex. cancer  tumor suppressor (proteins required for cancer prevention) and oncogenes (genes that make cell cancerous) are transcription factors  Ex. cures  inhibiting gene expression of pathogen = cure Central Dogma • DNA transcribed to RNA translated to Protein Why is there RNA? • The RNA step provides an amplification which allows genes to be expressed at different levels  Many identical RNA copies can be made from the same gene  Each RNA molecule can direct synthesis of protein molecules  Amplification allows cell to synthesize large amount of protein whenever
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