蛋白质化学讲义-1汇总.ppt

Classification of Proteins Shape of the molecules Composition Solubility Function Glycoprotein—Glycans is covalently bound to proteins or peptides. Glycoproteins Versatile functions—enzymes, hormones, interferons, lectins, memberane blocks, blood type recognition Structure characteristics—open or branched chains of sugar moieties composed of several type of sugars, including pentose (D-xylose), hexose (D-galactose), hexose derivatives (N-acetyl-D-glucosamine), sialic acid, etc. C-1 of sugar covalently bound to OH in amino acid side chains, or amide of asparagine. Solubility—most of them are water soluble. Physio-chemical Properties of Peptides and Proteins Zwitterionization and isoelectric point—least soluble at isoelectric point 兼性离子性质 Macromolecular properties—diffusion 扩散(centrifugation 应用：离心分离), viscosity 粘度, impermeability 不透过性 Denaturation 变性—destroy of non-covalent bonds in proteins Precipitation 沉淀—salts, heavy metals, alkaloids, organic solvents, heat Colorful reactions 呈色反应—biuret, ninhydrin, dansyl chloride UV adsorption 紫外吸收—280nm characteristic bands Chemical Interactions in Peptides The primary structure of proteins The primary structure includes: number of peptide bonds; The N and C terminal of peptide; number, type and sequence of amino acid in each peptide chain 氨基酸如何连接成肽链及在肽链中的排列顺序 The secondary structure of proteins: a-helix The secondary structure of proteins: b-pleated sheet The secondary structure of proteins Others: b-turn (rich in prolines) hairpin random coils 借助主链的氢键形成具有周期性的构象 Super-secondary structures, domains 结构域and motifs 模体: the structures between secondary and tertiary structures The tertiary structure of proteins The tertiary structure of proteins A peptide consists of different portions of a-helix, b-sheet, b-turn and random coil, which folds to a global conformation Non-polar side chains are buried in the hydrophobic core, while polar side chains exposed to the surface of the molecule Hydrophobic pockets near to the surf