山东农业大学分子生物Chapter1

Th Part ⅠThe structure ofproteins, Nucleic acids, andmacromolecular complexes pChapter1Macromoleculeschapter you will learnIn this• 1. The nature of the components of nucleic acids and proteins, and the chemical linkages by which they are joined to form larger molecules.• 2. The role that noncovalent interactions play in determining the three‐dimensional structure ofmacromolecules.A Typical Cell Contains Different kinds ofMolecules.•Small molecules inorganic ions and organic compounds whose molecular weights usually do not exceed several hundred.d d l h d d•macromolecules molecular weights from 104to 1012.protein, nucleic acid, and polysaccharide. They are polymers of amino acids, nucleotides, and sugars, respectively.Protein ispolymer of amino acidsof A Dipeptide from Two Amino AcidsPeptide bondFormation 肽键B li i i f f id By elimination of water to form a peptide grouptetrapeptideAPolypeptide chainP l tid h iAmino terminusCarboxyl terminusChemical of Nucleic AcidsStructuresuc e c ac d s a po y uc eot de;•A nucleic acid is polynucleotide;•that is, a polymer consisting of nucleotides.Each nucleotide has the three followingE h l tid h th th f ll icomponents.1sugar1. A cyclic five‐carbon sugar.N‐糖苷键酯2. A purine or pyrimidine base attached to the 1'‐carbonatom of the sugar by an N‐glycosylic bond.f h b l li b d3. A phosphate attached to the 5' carbon of thesugar by a phosphoester linkage.10Chemical Structures of Polysaccharides●Polysaccharides are polymers of sugars (glucose) orsugar derivatives.●Covalent bonds occur between many pairs of carbon atoms. This atoms has the effect of allowing one sugar unit tobe joined to more than two other sugars, which resultsin the formation of macromolecules.highly branched macromolecules●For example, the cell walls of many bacteria and plant cells are single gigantic polysaccharide molecules.ll i l i ti l h id l l11Noncovalent Interactions that Determine theThree‐Dimensional structuresThe coil•无规则卷曲random•氢键Hydrogen‐bonding•疏水相互作用The hydrophobic interaction •离子键Ionic bonds•范德华力Van der waals attraction12The Random Coil•The three‐dimensional configuration of a random coil chain is called a random coil; it is a somewhat compact and globular structure that changes p y gshape continually, owing to constant bombardment by solvent molecules.•Few nucleic acid or protein molecules exist in nature as random coils because there are manyd il b hinteractions between elements of the chains.13‐Hydrogen Bonding,(链内)y g•In RNA, int ra strand hydrogen bonds cause the polynucleotide strand to be folded.•In DNA, int er strand (链间) hydrogen bonds are responsible for the double‐stranded helical structure.•In proteins, int ra strand (链内) hydrogen bonds gives rise to several particular polypeptide chain configurations14hydrophobic interaction A is an interaction between two molecules that are somewhat insoluble in water.Stacked 堆积的Unstacked 未堆积的15•Base‐ring portions of stacking 碱基堆积Poorly soluble organic the bases tend to cluster, minimizing the contact with water molecules. The most efficient kind of clustering is one in which base‐stacking the faces of the rings are in contact,•苯丙氨酸的苯环倾向堆积；•alanine, leucine, isoleucine, and valine 倾向于非堆积聚集. •Hydrophobic interactions tend to bring distant hydrophobic parts of a polypeptide chain together.16A i i b d i th lt f tt ti•An ionic bond is the result of attraction between unlike charges.•At physiological pH several amino acid chains are ionized: negativelycharged carboxyl groups (aspartic and glutamic acids) and positively charged (lysine, histidine, andamino groups(lysine histidine arginine). These five amino acids thus can form ionic bonds.17• bonds tend to parts Ionic bring together distant of the chain. Ionic interactions can also be repulsive •They are destroyed by extremes of pH, which can Th d t d b t f H hi h change the charge of the groups, and by high concentrations of salt, shieldsalt the ions of which the charged groups from one another.•Ionic bonds are the strongest of the noncovalent interactions.18Van der Waals Attraction•Van der Waals forces exist among all molecules and are a result of both permanent dipoles(偶极子)and(子环)the circulation of electrons(电子环流).•The dependence of the attractive force between two atoms , in which r is theis proportional to1/r6distance between their nuclei.y g•The attraction is a very weak force and is significant only if two atoms are very near one another.19SummaryoftheEffects ofNoncovalent Interaction•The effect of noncovalent interactions is to constrain a linear h i f ld i h h diff i f h h i chain to fold in such a way that different regions of the chain, which may be quite distant from each other in a chain, are together20brought together.Macromolecule Isolation andCharaterization • convenient method The most and widely employedfor monitoring the protein purification scheme, and also for initial studies,characterization studies is electrophoresis.•This method consists of setting the protein sample on a solid support and establishing an electric field. •Positively charged proteins will migrate toward the cathode (negative pole), negativelypole)and charged proteins toward the anode (positive pole).21Macromolecule Isolation andCharaterizationAcrylamide 丙稀酰胺22Two ‐dimensional gel electrophoresis of proteins核酸的凝胶电泳Agarose gel 琼脂糖凝胶23Electrophoresis equipment24核酸电泳结果检测25。