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1、,Amino acids and structure acids and bases Protein structure myoglobin and hemoglobin,collagen Protein purification Chromatography of proteins Electrophoresis of proteins Protein sequencing,amino acids and protein,Proteins are the most versatile macromolecules in living systems and serve crucial fu

2、nctions in essentially all biological processes. They function as catalysts, they transport and store other molecules such as oxygen, they provide mechanical support and immune protection, they generate movement, they transmit nerve impulses, and they control growth and differentiation,Amino Acid,St

3、ereoisomers (stereo-isomer),The 20 standard amino acids,Ionization,,,,,amino acids,Basic Structure of an amino acid,L-Amino acid,D-Amino acid,The two enantiomers of amino acid,Enantiomers,Enantiomers are molecules that have opposite spatial configuration are said to be optically active. One enantiom

4、er will rotate polarized light a set number of degrees to the right. This is called the dextrorotatory isomer or (+) isomer. The other enantiomer will rotate the plane polarized light the same number of set degrees in the opposite left direction. This isomer is said to be a levorotatory isomer or (-

5、) isomer.,,The two enantiomers of an amino acid,,Hydrophobic aliphatic amino acids,Hydrophobic aromatic amino acids,,,Polar charged amino acids,,Polar uncharged amino acids,,The 20 standard amino acids,,Hydrophobic aliphatic amino acids,Gly :甘氨酸,glycine,Hydrophobic aliphatic amino acids,Ala:丙氨酸,,ala

6、nine,Hydrophobic aliphatic amino acids,Val:纈氨酸,valine,Hydrophobic aliphatic amino acids,Leu:亮氨酸,leucine,Hydrophobic aliphatic amino acids,isolcuci,Ile:異亮氨酸,Hydrophobic aliphatic amino acids,methionine,Met :甲硫氨酸,Hydrophobic aliphatic amino acids,proline,Pro :脯氨酸,Hydrophobic aliphatic amino acids,Cyst

7、eine,Cys :半胱氨酸,Hydrophobic aromatic amino acids,,Phe:苯丙氨酸,Phenylalanine,Hydrophobic aromatic amino acids,Tyr:酪氨酸,Tyrosine,Hydrophobic aromatic amino acids,Trp:色氨酸,Trptophan,Polar charged amino acids,Arg:精氨酸,Arginine,Polar charged amino acids,Lys:賴氨酸,Lysine,Polar charged amino acids,His:組氨酸,Histidine

8、,Polar charged amino acids,Aspartate,Asp :天冬氨酸,Polar charged amino acids,Glu:谷氨酸,Glutamate,Polar uncharged amino acids,Serine,Ser :絲氨酸,Polar uncharged amino acids,Thr:蘇氨酸,Threonine,Polar uncharged amino acids,Asn:天冬酰胺,Asparagine,Polar uncharged amino acids,Glutamine,Gln :谷氨酰胺,The 20 standard amino a

9、cids,acids 、bases and pH Buffer Ionization of amino acids,acids and bases,acids、bases and pH,An acid can be defined as a proton donor A base as a proton acceptor AcidH+ +base E.g: CH3COOH H++CH3COO- NH4+ H++NH3 The pH of a solution is a measure of its concentration of protons: pH=-lgH+,buffers,An ac

10、id-base conugate pair can act as a buffer,resisting changes in pH.,Ionization,Ionization,Nonionic form,Zwitterionic form,,Dissociation of amino acid,Titration curve of glycine,Peptide bond,Primary structure,Secondary structure,Tertiary structure,Quaternary structure,Protein Structure,peptide bond,Pe

11、ptide units within a polypeptide,Peptide Bonds Are Planar. In a pair of linked amino acids, six atoms (C a, C, O, N, H, and Ca) lie in a plane. Side chains are shown as green balls.,Primary structure,Amino Acids Are Linked by Peptide Bonds to Form Polypeptide Chains,Disulfide bond,Secondary structur

12、e,Secondary Structure: Polypeptide Chains Can Fold Into Regular Structures Such as the Alpha Helix, the Beta Sheet, and Turns and Loops. Can a polypeptide chain fold into a regularly repeating structure? In 1951, Linus Pauling and Robert Corey proposed two periodic structures called the a helix (alp

13、ha helix) and the b pleated sheet (beta pleated sheet). Subsequently, other structures such as the b turn and omega ( W ) loop were identified. Although not periodic, these common turn or loop structures are well defined and contribute with a helices and b sheets to form the final protein structure.

14、,,The folding of the peptide chain into an a-helix,-helix,-helix,H-bond,-sheet,Parallel and antiparallel -sheet,A Parallel b Sheet.,An Antiparallel b Sheet.,-sheet,,The folding of the peptide chain in a -turn,Super-secondary structure,Rossman M .G. 1973 ,STRUCTURAL DOMAIN,Tertiary structure,Water-S

15、oluble Proteins Fold Into Compact Structures with Nonpolar Cores Tertiary structure,refers to the spatial arrangement of amino acids that are far apart in the linear sequence as well as those residues that are adjacent.,H-bond in tertiary structure,Quaternary structure,Quaternary structure refers to

16、 the spatial arrangement of the polypeptide subunits and the nature of the interactions between them. These interactions may be covalent links or non-covalent interactions,Quaternary structure,Simple quaternary structure,,Levels of structure in proteins,Protein stability,Non-covalent interactions (

17、electrostatic forces,hydrogen bonds,hydrophobic forces ) covalent interactions ( disulfide bonds ) Peptide bonds,Protein folding,Spontaneously fold Hydrophobic force Ordered set of pathways Accessory protein: Protein disulfide isomerase Peptidyl prolyl cis - tran isomerase Molecular chaperone,myoglo

18、bin and hemoglobin,Oxygen-binding proteins Myoglobin 肌紅蛋白 Hemoglobin 血紅蛋白 Binding of oxygen to heme Allostery 別構 Mechanism of the allosteric change The bohr effect Fetal hemoglobin 胎兒血紅蛋白 Hemoglobinopathies 血紅蛋白病,Oxygen-binding proteins,Myoglobin and Hemoglobin are the two oxygen-binding proteins pr

19、esent in large multicellular organisms. Hemoglobin transports oxygen in the blood and is located in the erythrocytes; Myoglobin stores the oxygen in the muscles.,Myoglobin,Myoglobin structure,Hemoglobin,PROTOPORPHYRIN IX原卟啉,Heme血紅素,Ferriheme高鐵血紅素,animation,hemo,Allostery變構,Allosteric protein Coopera

20、tive Non-cooperative Oxygen dissociatio curves (Sigmoidal, hyperbolic),,Oxygen dissocation curves for Hb and Mb,The bohr effect,The bohr effect,Fetal hemoglobin,Fetal hemo,,B5 collagen,Function and diversity Biosynthesis Composition and post-translational modifications Structure Secretion and aggre

21、gation Cross-links Bone formation,collagen,collagen,collagen,COLLGEN SYNTHIESIS,COLLEGEN BOND,collgen,,,,,,Protein Solubility,Protein size,Protein charge,Protein specific binding affinity,B6 Protein Purification,,Selection of a protein source,,,Homogenization and solubilization,Stabilization of prot

22、eins,Assay of proteins,Principles of protein purification,,,Gel filtration chromatography,Ion exchange chromatography,Affinity chromatography,B7 Chromatography of proteins,Gel filtration chromatography,fig,Gel filtration chromatography,Gel filtration chromatography,Ion exchange chromatography,Affini

23、ty chromatography,,,,,Native PAGE,SDS-PAGE,Isoelectric focusing,B8 Electrophoresis of Protein,Visualization of proteins in gels,electrophoresis,Native polyacrylamide gel electropphoresis,,,,Determination of the molecular mass of unknown protein by electrophoresis,Isoelectric focusing,Isoelectric foc

24、using,Isoelectric focusing,Two-dimensional gel electrophoresis,Appearance of protein after electrophoresis,,,,,,,,,Amino acid composition analysis,Edman degradation,Sequencing strategy,B9Protein sequencing and peptide synthesis,Amino acid composition analysis,Hydrolized into amino acids Ion exchange

25、 chromatography Colorimetric比色 reaction(ninhydrin茚三酮,fluorescamine熒光胺),Edman degradation,fig,Recombinant DNA technology,The sequence of a protein can be determined using recombinat DNA technology to identify and sequence the piece of DNA encoding the protein. The amino acid sequence of the protein c

26、an then be deduced from its DNA sequencing using the genetic code.,Information derived from protein sequences,The amino acid sequence of a protein not only reveals the primary structure of the protein but also information on possible protein families or groups and evolutionary relationships,potential gene duplication and possible post-translational modifications. In addition,a knowledge of the amino acid sequence can be used to generate specific antibodies and DNA probes,,