Đề tài Protein

PROTEIN1PROTEINSComprise over 50% of dry mass of most cellsVery diverse in structure and functionConsist of one or more polypeptidesPolypeptides are chains of amino acids2PROTEINSProteins are polymers of amino acids20 different amino acidsDifferent “R” groupsSome hydrophilicSome hydrophobic3PROTEINSAmino acids are linked via condensation reactionsAmino acid of one reacts with the acid group of anotherForm covalent “peptide bonds”All proteins are made by assembling the same 20 amino acids in different orders to different lengths4PROTEINSHumans can make tens of thousands of distinctly different proteinsAll use the same 20 amino acidsDifferent ordersDifferent lengthsHow many distinctly different tripeptides can be assembled from these 20 amino acids?tetrapeptides?5ESSENTIAL & NONESSENTIALAll organisms require all 20 amino acidsHumans can manufacture only ten of these amino acids from precursor molecules*“Non-essential amino acids”Humans cannot manufacture the other ten amino acids“Essential amino acids”Must be acquired from dietThe bacterium Escherichia coli can manufacture all twenty amino acidsAll amino acids are nonessential for E. coli* Humans can produce 12 amino acids from precursor molecules, but the precursor molecules for the production of two of these 12 amino acids are themselves essential amino acids (met  cys, phe  tyr)6ROLES OF PROTEINSKey roles of proteinsStructuralMovementTransportChemical messengersReceptorsStorageDefensiveEnzymes7ROLES OF PROTEINSHormones are one group of proteinsChemical messengers involved in numerous processese.g., Insulin, glucagon, growth hormone, etc.Remember, not all hormones are proteinsSteroid hormones are lipidsOther hormones are proteins8ROLES OF PROTEINSEnzymes are biological catalystsOne important class of proteinsSpeed up the rate of chemical reactionsPerhaps 10,000 times fasterNot consumed in this reactionsHighly specific9PROTEIN CONFORMATIONEach protein folds up into a particular three-dimensional shapeProtein function is related to its structure10PROTEIN CONFORMATIONEach protein folds up into a particular three-dimensional shapeFour levels of protein organization are recognizedPrimary (1o) structureSecondary (2o) structureTertiary (3o) structureQuaternary (4o) structure11PROTEIN CONFORMATIONPrimary structureLinear sequence of amino acidsGenetically determinedUltimately determines higher structural levelsThe primary structure of the enzyme lysozyme is depicted129 amino acids long12PROTEIN CONFORMATIONSome regions of the polypeptide exhibit secondary structureFormed by H-bonding at regular intervals along the polypeptide backboneTwo common types of secondary structureAlpha-helicesBeta-pleated sheets13PROTEIN CONFORMATIONTertiary structure involve interactions among R-groupsFour main factorsHydrogen bondsIonic attractionsHydrophobic interactionsCovalent bonds“Disulfide bridges”14PROTEIN CONFORMATIONQuaternary structure results from interactions between multiple polypeptide chainsNot all proteins possess multiple polypeptide chainsNot all proteins possess quaternary structure15PROTEIN CONFORMATION16PROTEIN CONFORMATIONThe three-dimensional conformation of a protein is critical to its functionForm determines functionAltered conformation can compromise functionAltered structure at any level can alter the final conformationAltered chemical bonds can alter conformation17MUTATION & CONFORMATIONThe primary structure of a polypeptide is genetically determinedPrimary structure ultimately determines the final shape of a proteinMutations can alter the DNA sequence of a geneCan alter the primary structure of the polypeptideCan result in an altered three-dimensional shapeBasis of many genetic disorders18PROTEIN DENATURATIONProteins can be denatured by a variety of factorsTemperaturepHetc.Denaturation alters the conformation of the proteinOften irreversibleIt is difficult to “un-hard-boil” an egg19 ROLES OF PROTEINS	Structural proteinse.g., Collagen, elastin, keratin, etc.20ROLES OF PROTEINSProteins facilitating movemente.g., Actin, myosin, tubulin, etc.21ROLES OF PROTEINSTransport proteinse.g., Hemoglobin, lac permease, etc.22ROLES OF PROTEINSChemical messengerse.g., Hormones and neurotransmittersReceptorsRespond to chemical messengers23ROLES OF PROTEINSStoragee.g., Casein, ovalbumin, etc.24ROLES OF PROTEINSDefensivee.g., Antibodies, fibrin, etc.25ROLES OF PROTEINSEnzymesHighly specific catalysts of chemical reactions26REFERENCESCampbell, Neil A. and Reese, Jane B. Biology, 7th edition. Pearson Education, Inc. 2005.Campbell, Neil A., Reese, Jane B., Taylor, Martha R., and Simon, Eric J. Biology, Concepts and Connections, 5th edition. Pearson Education, Inc. 2006.Nester, Eugene W., Anderson, Denise G., Roberts, C. Evans Jr., and Nester, Martha T. Microbiology, A Human Perspective, 5th edition. McGraw-Hill Companies, Inc. 2007.Limson, Janice. 2002.