Chapter 14 notes

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Sections 14.9, 14.10, 14.11, and 14.12. Chapter 14 notes. Hannah Nowell and Jenny Sulouff. Random coil Wheat. Secondary Structure of a Protein 14.9. α helix. Secondary structure. Repeating patterns created by folds Two most common α- helix β -pleated - PowerPoint PPT Presentation

Transcript of Chapter 14 notes

Chapter 14 notes

Chapter 14 notesSections 14.9, 14.10, 14.11, and 14.12Hannah Nowell and Jenny Sulouff

Secondary Structure of a Protein14.9

Random coilWheat helixSecondary structureRepeating patterns created by folds Two most common- helix-pleated1940s -proposed by Linus Pauling and Robert CoreyHydrogen bond between the backbone C=O and N-H- Distinguishes a secondary structure and a tertary structure

Secondary Structure (con.)A R group can replace the hydrogen bonding On side chainsHydrogen bond between the backbone C=O and N-H- Distinguishes a secondary structure and a tertiary structureA R group can replace the hydrogen bonding On side chainsRandom CoilDoes not show any signs of a repeating patternMain structure of a proteinMost proteins are not mainly - helix or -pleatedThe remainder is a random coilEspecially common in globular proteins Mostly soluble in waterMainly only used for nonstructural purposes

-helixResembles a right-handed springA helixThe twists are kept by intramolecular hydrogen bondsBetween the backbone C=O and H-N-Hydrogen bond between the C=O and H-N-Maintain the helical shape-C=O point downH-N-point upAll amino acid side chains point away from the helix- pleated sheetThe alignment of the protein chains are maintained by intermolecular or intramolecular hydrogen bondsWhen peptide chains run parallelN- terminal ends are on one sideOr when they are antiparallelNeighboring N-terminal ends are alternating sidesCan occur when a hairpin structure is formed when a polypeptide makes a U-turnPleated sheet is antiparallel

- pleated sheet (con.)Microcrystals are deposited in the fiber axis, during the formation of -pleated sheets Can occur when a hairpin structure is formed when a polypeptide makes a U-turnPleated sheet is antiparallel Microcrystals are deposited in the fiber axis, during the formation of -pleated sheets Microcrystals are found in Spider silk and silkworm silkAllow the silk to be super strength and toughness Unmatched by synthetics

Fibrous protein-pleated sheetsKeratin Hair FingernailsHornsWool Fibroin Silk

Extended HelixMade of collagenRepeated unitsThe third amino acid is a glycineShortest of all the amino acid chainsProtein of connective tissues; bones, skin, tendons, etc. Gives protein strength and elasticity 30% of the bodys protein

Tertiary Structure of a Protein14.10

Tertiary Structures3D arrangement of the atoms in a proteinRefers to the conformation or shape that is different for every protein moleculeInteractions between the amino acids side chainsThere are five ways to stabilize a tertiary structure; covalent bonds, hydrogen bonding, salt bridges, hydrophobic interactions, metal ion coordination

Covalent bonds and hydrogen bondingCovalent bondsMost commonly usedDisulfide bondFormation of a disulfide bond allows covalent linkage, which binds the two chains togetherHydrogen bondingBetween polar chainsOn side chains between side chains and a peptide backbone

Salt bridgesSalt bridgesAlso called electrostatic attractionsBetween a acidic amino acid (-COO-) and a basic amino acid (-NH3+)It is a simple ion-ion attractionHydrophobic InteractionsHydrophobic InteractionsAqueous solutionPolar groups turn outward, towards aqueous solvent; Non-polar turn inward, away from water moleculesSeries of Hydrophobic interactions occurThe hydrophobic bond is weaker then the hydrogen bonding and salt bridgesActs over large areasCan stabilize a loop and other tertiary structures

Metal ion coordination Same charge side chains linked by a metal ionEx:Two glutamic acid side chains are attracted to magnesium ion Forms a bridgeHuman body needs selected trace minerals for components of proteinsChaperonesBiologically active conformation is caused by a protein that helps other proteinsHelps stabilize polypeptide chains prevents folds that would cause biologically inactive molecules

Quaternary Structure of a Protein14.11

Quaternary structureSpatial relationship along with the interactions of subunits in a protein that consists of multiple polypeptide chainsDetermines how subunit are organizedOne of the four levels of protein structuresHydrogen bonds hold and pack the subunits togetherAlong with salt bridges and hydrophobic interactions hold and pack them together

HemoglobinMade of four chains, chains are called globinTwo identical -chains which consist of 141 amino acid residues Two identical -chains which consist of 146 residuesChains containing non-amino acids are called conjugated proteinsThe non-amino acid part is called a prosthetic group CollagenHigh organization of subunitsTriple helix is called tropocallagenFound in only fetal or young connective tissuesAs it ages it organizes into fibrils cross link Insoluble Cross linking consist to covalent bonds Link together in two lysine residuesEx. Of tertiary structures Integral membrane proteinsTraverse completely or partially into a membrane bilayer1/3rd of all proteins The outer surface is nonpolarInteracts with lipid bilayerTwo quaternary structures6-10 -helices that cross the membrane-barrels consisting of 8, 12, 16, or 18 -sheets that are antiparallel How Proteins are Denatured14.12

What is Denaturation?Any type of chemical or physical agent that can destroy the structure of a proteinThe structure becomes a random shape proteinThe agents do not break the peptide bonds so the sequence of amino acids remain the same.Only effects a secondary, tertiary, or quaternary structures not a primary structureDenaturing a primary structure would cause a change in the arrangement of amino acids

Protein DenaturationDenaturing AgentAffected RegionsHeatH bondsDetergentsHydrophobic regionsAcids, basesSalt bridges, H bondsSaltsSalt bridgesReducing agents and Heavy metalsDisulfide bondsAlcoholHydration layers Reversible DenaturationIf the change in the protein is only minor than denaturizing can be reversed. By chaperonesNot all denaturation can be reversed. Ex. A hard boiled egg can not be un boiled.