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1、 Chapter 19 Biomolecules:Amino Acids,Peptides,and Proteins19.1 Structures of Amino Acids19.2 Isoelectric Points19.3 Peptides and Proteins19.4 Peptide Synthesis19.5 Classification of Proteins19.6 Protein StructureAmino acids(氨基酸氨基酸):Alanine(丙氨酸丙氨酸)Peptides(肽肽):Many Chains with fewer than 50 amino aci
2、dsAmide bondsProtein:(蛋白质蛋白质)For larger chains19.1 Structures of Amino AcidsDipolar ionZwitterion(偶极分子偶极分子)Amino acids are amphoteric(两性离子两性离子):In base solution:In acid solution:20-amino cids found in protein.19 of the 20amino acids are primary amines;Proline(脯氨酸脯氨酸)is a secondary amine.P476,Table 1
3、5.1Differ only in the nature of side chain.Glycine(甘氨酸甘氨酸)(S)-AlanineL-Alanine(S)-PhenylalanineL-Phenylalanine(s)-SerineL-SerineL-Glycer-aldehydeAspatic acid(天冬氨酸天冬氨酸)Glutamic acid(谷氨酸谷氨酸)AcidicLysine(赖氨酸赖氨酸)arginine(精氨酸精氨酸)Histidine(组氨酸组氨酸)basicThe others are neutral amino acids.19.2 Isoelectric Po
4、ints(等电点等电点)pHLow pH(protonated)High pH(deprotonated)Isoelectric Points(pI):At some intermediate pH,the concentrationof the dipolar ion is maximal,the concen-trations of the anions and cations are equal.pI pH=5.05.6Neutral amino acid:acidic amino acid:pI at lower pHbasic amino acid:pI at higher pHSe
5、paration of a mixture of amino acids by Electrophoresis(电泳电泳).-+LysinepI=9.74GlycinepI=5.97Aspartic acidpI=2.77Paper strip at pH=5.97C-terminal Amino acids polymers linked together by amide bonds.Peptide bond19.3 Peptides and ProteinsAlainine(Ala)Serine(Ser)Alanylserine(Ala-Ser)(丙氨酰丙氨酰-丝氨酸丝氨酸)(丙丙-丝二
6、肽丝二肽)Dipeptide(二肽二肽)Tripeptide(三肽三肽)Proteins:MW:10000N-terminal19.4 Peptide Synthesis1.Protection of the amino group by BOC 2.group:Ex.:Synthesis of Alanine-Leucine:AlanineDi-tert-butyldicarbonateBoc-Ala2.Protection of the carboxyl group by treatment with methanol or benzyl alcohol:BOC group can be
7、removed by CF3COOHThe groupscan easily beremovedby NaOH(aq).3.The two protected amino acids are coupled using DCC.Dicyclohexylcarbodiimide(DCC)(二环己基碳二亚胺二环己基碳二亚胺)4.Removal of the BOC group.5.Removal of ester group.19.5 Classification of Proteins19.5.1.Classification according to the composition1.Simp
8、le proteins:Blood serum albumin(血清蛋白血清蛋白),Globin(球蛋白球蛋白).2.Conjugated proteins(结合蛋白结合蛋白):Glycoprotein(糖蛋白糖蛋白),Hemoglobin(血红蛋白血红蛋白).19.5.2.Classification according to the three-dimensional shape1.Fibrous proteins:Collagen(胶原蛋白胶原蛋白),keratin(角蛋白角蛋白).Tough and insoluble in water.2.Globular proteins:Hemo
9、globin,Insulin(胰岛素胰岛素),Enzymes(酶酶).Soluble in water.19.6 Protein Structure The primary structure of a protein:The amino acid sequence.The secondary structure of a protein:The segments of the peptide backbone (肽链肽链).The tertiary structure of a protein:The three-dimensional shape of the entire protein molecule coiled.Two kinds of The secondary structure of aprotein:1.-Helix(-螺旋螺旋)-Keratin(-角蛋白角蛋白)2.-Pleated sheet（-折叠型折叠型)The-Pleated sheet structure presentin silk fibroin(蚕丝蛋白蚕丝蛋白)