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Lecture 4

BCH210 2014 Lecture 4.pdf

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Stavroula Andreopoulos

Lecture 4 Protein Structureproteins are classed according to shape and solubilityshape globular or fibrous4 levels of protein structure 1 Primarysequence 2 Secondarylocal structures Hbonds beta sheet alpha helix 3 Tertiaryoverall 3D shape assembly of secondaryunstructured segmentsfunctional protein 4 Quaternarysubunit organizationassemblyone covalent chain of a protein interacts with another to form a functional unitPrimary Structure 1the amino acid sequence Go from Nterminus to Cterminus Secondary Structure 2repeating conformations in the polypeptide chainperiodic repetitive units Proteins have been seen to have periodicalrepetitive units that feature throughout all of the protein worldalphahelix betasheetusually stabilized by intramolecular HbondingTertiary Structure 3assembly of secondaryunstructured segments into functional proteinall alpha helices beta sheets and unstructured segments are all assembled together completely folded and compacted proteindomain globular unit of the chaino there are 3 domains Quaternary Structure 4assembly of multisubunit protein o DimerTwo units togethero TetramerFour units togetherEg Hemoglobin2 alpha chains 2 beta chainsheterotrimerOne covalent chain of a protein has interaction with another or other chains to form a functional unito Unit protein performs its functionsThis protein has 6 different subunits that come together to make a tetramer When the subunits are the samehomotrimerWhen the subunits are different heterotrimerSubunits are held together through noncovalent interactions Hbonding van der waals electrostatic etcProtein Structure and Function and Tightly Linkedthe 3 dimensional structures of proteins and their biological functions are linked by several overarching principles o function depends on structure primary amino acid sequence o structure depends on sequence and on weak noncovalent forces Hbonds VDW ionic hydrophobic effects o the number of protein folding patterns is large but finite only one native conformation o structures of globular proteins are marginally stable can be denatured quicklyProtein Shapes Waymany are watersoluble compact roughly spherical macromolecules whose polypeptide chains are tightly foldedo hydrophobic line the inside hydrophilic line the outsidepolypeptides can also be components of large subcellularextracellular structures such as ribosomes flagella and
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