acids(氨基酸).ppt

1、Chapter 19 Biomolecules: Amino Acids, Peptides, and Proteins,19.1 Structures of Amino Acids 19.2 Isoelectric Points 19.3 Peptides and Proteins 19.4 Peptide Synthesis 19.5 Classification of Proteins 19.6 Protein Structure,Amino acids(氨基酸):,Alanine (丙氨酸),Peptides(肽):,Chains with fewer than 50 amino ac

2、ids,Protein: (蛋白质),For larger chains,19.1 Structures of Amino Acids,Dipolar ion,Zwitterion,(偶极分子),Amino acids are amphoteric(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) is a secondary amine.,P476,Table 15.1,Diff

3、er only in the nature of side chain.,Glycine(甘氨酸),L-Glycer- aldehyde,The others are neutral amino acids.,19.2 Isoelectric Points(等电点),Isoelectric Points (pI):,At some intermediate pH, the concentration of the dipolar ion is maximal, the concen- trations of the anions and cations are equal.,pI pH=5.0

4、5.6,Neutral amino acid:,Separation of a mixture of amino acids by Electrophoresis(电泳).,Paper strip at pH=5.97,C-terminal,Amino acids polymers linked together by amide bonds.,Peptide bond,19.3 Peptides and Proteins,Dipeptide(二肽),Tripeptide(三肽),Proteins: MW: 10000,19.4 Peptide Synthesis,Protection of

5、the amino group by BOC group:,Ex.: Synthesis of Alanine-Leucine:,2. Protection of the carboxyl group by treatment with methanol or benzyl alcohol:,BOC group can be removed by CF3COOH,The groups can easily be removed by NaOH(aq).,3. The two protected amino acids are coupled using DCC.,Dicyclohexylcar

6、bodiimide (DCC)(二环己基碳二亚胺),4. Removal of the BOC group.,5. Removal of ester group.,19.5 Classification of Proteins,19.5.1. Classification according to the composition,1. Simple proteins:,Blood serum albumin(血清蛋白), Globin(球蛋白).,2. Conjugated proteins(结合蛋白):,Glycoprotein (糖蛋白), Hemoglobin(血红蛋白).,19.5.2

7、. Classification according to the three-dimensional shape,1. Fibrous proteins:,Collagen(胶原蛋白), keratin(角蛋白).,Tough and insoluble in water.,2. Globular proteins:,Hemoglobin, Insulin(胰岛素), Enzymes(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).,The tertiary structure of a protein: The three-dimensional shape of the entire protein molecule coiled.,Two kinds of The secondary structure of a protei