Chapter1StructureandFunctionofProteins.ppt

Section I The composition and  constitution of protein Element composition: C (50~55%) H (6~7%) O (19~24%) N (13~19%) S (0~4%) P, metal elements,Ⅰ ◆ Average 16% of nitrogen in proteins 2. Classification of amino acids Classified according to polarity（极性） of R group: Hydrophobic -water fearing （疏水性） non-polar R group Hydrophilic -water loving （亲水性） polar, neutral chains negatively charged positively charged 3. Properties of amino acids (2) Peptide 肽 Peptide 肽 Peptides (made of different AAs) have different isoforms Gly-Ala, Ala-Gly Gly-Ala-Lys, Gly-Lys-Ala, Ala-Gly-Lys, Ala-Lys-Gly, Lys-Ala-Gly, Lys-Gly-Ala, (1 x 2 x 3 x 4 x 5……… x n) (3) Important Peptides Glutathione (GSH) Functions of GSH Antioxidant 2GSH + H2O2 → GSSG + 2 H2O GSSH + NADPH + H+ → 2GSH + NADP 5. Proteins Protein: a macromolecule composed of one or more polypeptides, each polypeptide chain folds up to form a specific shape. Primary structure The AA sequence from N end to C end in the polypeptide chain(s) of a protein Numbering AA sequence from N to C end Forces that stabilize the primary structures are covalent bonds— peptide bonds and disulfide bonds (if present). The AA sequence of a protein is determined by its gene. 2. The secondary structure 二级结构 The localized folding segments of the polypeptide backbone. Common secondary structures: α-helix (α螺旋) β-pleated sheet (β折叠) random coil (无规卷曲) β-turn(bend)(β转角) Forces: hydrogen bonds Peptide unit definition Peptide unit (plane) (2) α-helix (2) α-helix (2) α-helix α－螺旋结构 多肽链的主链围绕中心轴有规律的螺旋式上升,螺旋走向为顺时钟,即右手螺旋; 氨基酸残基侧链