【正文】 Molecular Biology 大連理工大學 Noncovalent interactions that determine the threedimensional structure of macromolecules ? The biological properties of macromolecule are mainly determined by activating interactions that results in each molecule acquiring a unique threedimensional structure. ? These noncovalent interactions are much weaker than typical covalent bonds, and for any given type of macromolecule, several of these weaker interactions may play a role in determining threedimensional structure. Molecular Biology 大連理工大學 Noncovalent interactions ? The Random coil 纏 繞 – Linear polypeptide and polynucleotide chains contain bonds about which there is free rotation. – In the absence of any intrastrand（分子內） interactions, each monomer would be free to rotate with respect to its adjacent monomers – Few, if any, nucleic acid or protein molecules exist in nature as random coils because of many interactions between elements of the chains – Noncovalent interactions ? Hydrogen bonds 氫鍵 ? The hydrophobic interaction 疏水作用 ? Ionic bonds 離子鍵 ? Van der waals attraction 范德華力 Molecular Biology 大連理工大學 effects of noncovalent interactions ? Determine the three dimensional structures of macromolecules. – Constrain(約束 ) a linear chain to fold in such a way that different regions of the chain, are brought together. ? Disulfide bonds(二硫鍵 。 covalent) also affects the molecular properties of proteins. Molecular Biology 大連理工大學 Macromolecule isolation and characterization ? Proteins – Molecular sieves 分子篩 : molecular weight – Chromatography 層析 : charge (positively or negatively charged) or affinity properties – Electrophoresis 電泳： SDSPAGE, charge and size。 most convenient method – Ultracentrifugation 超離心 – Amino acid sequencing – Xray crystallography x射線晶體學 – Electron microscopy 電子顯微鏡 Molecular Biology 大連理工大學 Macromolecule isolation and characterization ? Nucleic acid – Gene cloning – PCR: polymerase chain reaction – Molecular sieves: molecular weight – Electrophoresis: Agarose gel, most convenient method – Ultracentrifugation – Nucleotide sequencing – Electron microscopy Molecular Biology 大連理工大學 Summary ? Structural characteristics of macromolecules ? Components of macromolecules ? Noncovalent interactions ? Covalent bonds ? Bonds for determining threedimensional structure ? Methods for isolation and characterization of protein and nucleic acids Molecular Biology 大連理工大學 Important concepts and aspects you are required to understand ? Small Molecules vs Macromolecules ? Monomers, Polymers and Macromolecules ? Common Monomers in Cells ? What AA have in mon? Exception ? What make AA unique? ? Different categories of AA and their special features: form H bonds, salt bridges, disulfide bond, responsible for UV absorbance, etc ? D and L forms of AA ? 4 different levels of protein structures and their features: basis of structures, bonds involved ? Chemical ponents of DNA and their positions in double helix structure ? Important forces in maintaining DNA stibilization ? Difference between DNA and RNA ? D and L sugars ? Monosaccharides ? Disaccharides ? Polysaccharides ? Polysaccharides’ major roles ? Peptide bond ? Disulfide bond ? glycosidic bond ? Structural characteristics of lipids ? Noncovalent interactions ? Methods for protein isolation and characterization ? Methods for nucleic acid isolation and characterization The end of chapter 2 Molecular Biology 大連理工大學 Chapter 6 The Geic Materi