Protein Structure

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PROTEIN STRUCTURE Brianne Morgan, Adrienne Trotto, Alexis Angstadt

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Protein Structure. Brianne Morgan, Adrienne Trotto , Alexis Angstadt. Secondary Structure 14.9. A repetitive structure of the protein backbone. The two most common secondary structures encountered in proteins are the α-helix and the β-pleated sheet. - PowerPoint PPT Presentation

Transcript of Protein Structure

Protein Structure

Protein Structure Brianne Morgan, Adrienne Trotto, Alexis AngstadtSecondary Structure 14.9A repetitive structure of the protein backbone.The two most common secondary structures encountered in proteins are the -helix and the -pleated sheet.The protein conformations that do not exhibit a repeated pattern are called random coils.

HelixIn the -helix form, a single protein chain twists in such a manner that its shape resembles a right-handed coiled spring-that is, a helix. The shape of the helix is maintained by numerous intramolecular hydrogen bonds that exist between the backbone C=O and H-N- groups. All the amino acid side chains point outward from the helix.

B-pleated sheetIn this case, the orderly alignment of protein chains is maintained by intermolecular or intramolecular hydrogen bonds. The -pleated sheet structure can occur between molecules when polypeptide chains run parallel (all N-terminal ends on one side) or antiparallel (neighboring N-terminal ends on opposite sides.)

Few proteins have predominately -helix or -sheet structures.Most proteins, especially spherical ones, have only certain portions of their molecules in these conformations. The rest of the molecules consist of random coil.

Keratin is a fibrous protein of hair, fingernails, horns, and wool and it doesnt have a predominately -helix structure.

Extended HelixAnother repeating pattern classified as a secondary structure is the extended helix of collagen.

Tertiary Structure 14.103-D arrangement of every atom in the moleculeIncludes interactions of side chains, not just the peptide backboneStabilized in 5 ways: Covalent Bonds, hydrogen bonding, salt bridges, hydrophobic interactions, metal ion coordinationCovalent BondsDisulfide bond is most often involved in the stabilizationWhen a cysteine residue is in 2 different chains, formation of a disulfide bond provides a covalent linkage that binds together the 2 chains EX: structure of insulin

Hydrogen BondingStabilized by hydrogen bonding between polar groups on side chains or between side chains and the peptide backboneSalt BridgesAlso called electrostatic attractionsOccur between 2 amino acids with ionized side chainsHeld together by simple ion-ion attraction

Hydrophobic InteractionsResult of polar groups turned outward toward the aqueous solvent and the nonpolar groups turned inward away from the water moleculesWeaker than hydrogen bonding or salt bridgesActs over large surfacesMetal Ion Coordination2 side chains can be linked with a metal ionHuman body requires certain trace mineralsNecessary components of proteinsPrimary structure of a protein determines the secondary and tertiary structureWhen particular R- groups are in proper position, all of the stabilization can formThe side chains allow some proteins to fold

Quaternary Structure of a Protein 14.11The highest level of protein organizationApplies to proteins with more than 1 polypeptide chainHemoglobinEach chain surrounds an iron- containing heme unitProteins that contain non-amino portions are called conjugated proteinsThe non-amino acid portion of a conjugated protein is called a prosthetic groupEarly development stage of the fetus, hemoglobin contains 2 alpha and 2 gamma chainsCollagenThe triple helix units called tropocollagen constitute the soluble form of collagenStructural protein of connective tissue Provides strength and elasticityStabilized by hydrogen bonding between the backbones of the 3 chainsMost abundant protein in humans

Integral Membrane ProteinsTraverse partly 1/3 of proteins

How are Proteins Denatured? 14.12Secondary and tertiary structures stabilize the native conformations of proteinsPhysical and chemical agents destroy these structures and denature proteinsProtein functions depend on native conformation; when a protein is denatures, it can no longer carry out its functionSome is reversible, some chaperone molecules may reverse denaturation