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regulating protein function.docx

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Richard B Day

thJanuary 15 2013 Biology 2B03 Cell Biology Regulating Protein Function Protein Foldingpolypeptides can begin to fold into secondary and tertiary structures while being synthesizedany polypeptide chain has the potential to adopt a vast number of conformations but there is usually a single correct formnative statenative state lowest energy state most thermodynamically stable form of the polypeptide chain Unique native state for unique peptide sequencespend the majority of their time in their native stateprotein folding iseasyspontaneousreversible can unfold and refold into native stateunique for a single polypeptide sequence it will have a unique configurationall of the information required to specify the fold is contained within the sequence of aminoacids that make up the proteinREAD Baker D 2000 A surprising simplicity to protein folding Nature 405 3942Spontaneous SelfAssembly of Proteinsreversible denaturation experimentdenatured the protein forcing it to unfold8M Urea breaks H and hydrophobic bondsmercaptoethanol breaks disulphide bridges disrupted noncovalent and covalent bondsdialysis removes denaturantsrenaturation of protein in vitro occurs spontaneouslythe information for folding a protein lies in its sequenceprotein folded back into its native conformationother denaturants of proteinstemperaturepH Animation of Protein Foldingproteins mostlikely fold by a process of trial and error they try various conformations until they find the most stable single conformationfolding of vilin protein small and fastIs Folding Important What are the Consequences of Misfoldingfailure of proteins to fold correctly or to remain folded can give rise to a wide range of pathological conditionseg in each case a single amino acid changehereditary disorders cystic fibrosis emphysema Alzheimers diseaseprionbased diseases CreutzfeldJacob disease Mad Cow diseaseCorrectly Folded Proteins have a Specific Functionhereditary misfolding disordersif the protein is not folded correctly it may be in the wrong cellular location have no function or sometimes it may even be detrimental to the systemexamplessickle cell anemia misfolded haemoglobinchanges red blood cell shapehaemoglobin tetramer four subunitsconfirmation differs with oxygen2 stable conformationsglutamic acid replaced by valine at position 6 each tetramer are aggregating together changing the same of the blood cells which cannot bind to oxygen 1 emphysema antitrypsin variants are unstable or exhibit very slow foldingrequired in the cells of lungs to maintain its elasticityD256V or aspartate to valine at position 256Variants interact with each other and aggregate to form a very long polymerGives it a quaternary structure which it did not have before Prionsbased diseasesfatal familial insomnia kuru and CreutzfeldtJakob disease human scrapie sheep chronic wasting disease deer and elk and bovine spongiform encephalopathy BSE or mad cow diseaseneurodegenerative disordersprion infectious agent that is protein based can be passed from one organism to the next
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