CHAPTER 3 Protein Structure And Function (got 94% in the course)

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Louisiana State University
Biological Sciences
BIOL 3090

CHAPTER 3 Protein Structure and FunctionProteins are the most diverse of the macromolecules in terms of structure and functionA proteins threedimensional structure is called its conformationCorrect folding is absolutely critical for protein functionFunction is derived from structurePeptides short polymers formed by the ordered linking of amino acidsMEMORIZE the amino acidsFIG 33a2 molecules goes through dehydration reaction and a covalent bond peptide bond is formedA small peptide of five amino acids count the alpha Cs FIG 3bPeptide short chain of amino acids 230 residuesPolypeptide longer chain up to 4000Protein a polypeptide that has folded into a specific formationLevels of Protein StructurePrimary structurelinear sequence of amino acidsoSpecific amino acid sequence contains all the intrinsic information on how a protein folds into its 3D structureSecondary structureoAlphahelixCarbonyl O is Hbonded to an amide nitrogen four peptide bonds downstreamFIG 33bR groups side chains dont contribute directly They point outward FIG 34All the carbonyl groups are pointed down all the amide nitrogens are pointed upThese carbonyls and amides have partial chargesandrespectivelyThese partial charges are cumulativeThus the alpha helix has a dipoleHas both polar and non polar regions is amphipathicoBetastrand60 of an average proteins 3D structure alpha and beta58 amino acids per strandAgain Hbonds between backbone amide and carbonyl groups hold one strand to anotherResults in pleated sheetRgroups project above and below the sheetoBeta turn reverse turn FIG 36Usually 4 amino acids forming a UturnRedirects the polypeptide chainGlycine and Proline often found in Reverse turnTwo of the three special amino acidsGly and Pro often referred to as helix breakersThe lack of a large sidechain in glycine and the built in bend in proline allow polypeptide to fold into UshapeoRandom coil loopsConnects alpha helices and beta sheetsNo defined structureBut we like to include it as an important structural feature basically because it sounds coolTertiary StructureoOverall folding of the chain into a specific 3D structureoInteractions needed for folding are
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