中南大学生物化学考研课件ch4氨基酸aminoacids.ppt

1、Biochemistry,For Specialty of Biotechnology or Bioengineering at CSU Mr. XIA Jinlan,Chapter 4 Amino acids 氨基酸,Amino acids, just like this image, have their mirror image symmetry. 正像这副图画，氨基酸分子具有镜像对称性。,Main Contents,Basic knowledge 基本知识 Definition 定义 The 20 common amino acids 常见氨基酸 Some uncommon amino

2、 acids 非常见氨基酸 Acid-base chemistry of amino acids 氨基酸酸碱化学 Ionization 离解作用 Reactions of amino acids 氨基酸反应 Optical activity and stereochemistry of amino acids 氨基酸光学活性和立体化学 Stereoisomers 立体异构体 Separation and analysis of amino acid mixture 氨基酸混合物的分离和分析,Definition of amino acids 定义,Three parts:,Basic know

3、ledge,脂肪酸侧链,a手性碳原子,Anatomy of an amino acid 结构剖析,Ball-and-stick model 球棍模型,Tetrahedral structure 四面体结构,Basic knowledge,Perspective drawing 透视画法,Normal structure,Exceptions 例外,Basic knowledge,Classification 分类 Nomenclature 命名法,The 20 common amino acids 常见氨基酸,Need to know:,Basic knowledge,Classificati

4、on 分类 Most useful way based on the polarity of the side chains 最有用的分类方式是根据氨基酸侧链的极性,Nonpolar or hydrophobic amino acids 非极性或疏水性氨基酸 Polar, uncharged amino acids 极性， 不带电氨基酸 Acidic amino acids (with a net charge at pH7.0) 酸性氨基酸 （在pH7时带净负电荷） Basic amino acids (with a net + charge at pH7.0) 碱性氨基酸（在pH7时带净正

5、电荷）,See table 4.3 and 4.4,Nomenclature 命名法,Three writing forms Complete Name 全名 Abbreviation in three letters三字母缩写名称 Abbreviation in one letter单字母缩写名称,Typical examples: 亮氨酸 Leucine (Leu, L) 谷氨酸 Glutamic acid (Glu, E) 谷氨酰胺 Glutamine (Gln, Q) 异亮氨酸 Isoleucine (Ile, I),See Figs. 4.3 and 4.4,Please note:

6、 Besides the 20 common amino acids, there are still 1. Some uncommon amino acids in proteins 存在于蛋白质中的非常见氨基酸 2. Some uncommon amino acids not found in proteins 不存在于蛋白质中的非常见氨基酸,Uncommon amino acids-self-study 非常见氨基酸-自学,请把p87页的“Amino Acids Not Found in Proteins” 翻译成汉语。,Acid-base chemistry,Amino acids a

7、re weak polyprotic acids 氨基酸是多元弱酸,Ionization 离解作用,With poly-grade ionization steps 多步离解 pK: ionize constant 离解常数 With an isoelectric point (pI) pI: a pH at which the amino acid has no charge 等电点时氨基酸不带电荷,Termination of pKs and pI （pKs和pI的表示）,pI=(pK1+pK2)/2,Take glycine as an example 以甘氨酸为例,pI=(pK1+pK

8、2)/2,k2,k1,pI=(pK1+pK2)/2,k2,k3,k1,pI=(pK2+pK3)/2,k1,k2,k3,Formation of peptide bond,Amino end N terminal 氨基端， 或 N端,Carboxyl end C terminal 羧基端 或 C端,Reactions of amino acids,N,C,“sense” 方向,Reactions of amino acids,Ninhydrin reaction茚三酮反应,Purple 紫色,Ninhydrain 茚三酮,Optical activity and stereochemistry

9、光学活性和立体化学,Amino acids are chiral molecules, which have optical rotatory behavior 氨基酸是手性分子，它们具有光学旋光现象 Dextrorotatory: + 右旋 Levorotatory: - 左旋 Chiral molecules are nomenclatured in two ways 手性分子的两种命名方式 D, L system (D=dextro 右, L=levo 左) R, S system (R=Latin rectus=right; S=Latin sinistrus=left),Enanti

10、omers: mirror image isomers 对映异构体：镜像对称异构体,Optical activity and stereochemistry,Mirror image 镜 像 对 称,L- (levo=左); D- (dextro=右),D, L system is referring to D or L-glyceraldehyde D，L系统是参照D或L-甘油醛,Exceptions without mirror image symmetry,甘氨酸 Glycine,脯氨酸 Proline,R, S system is referring to: R=Latin rectu

11、s=right; S=Latin sinistrus=left,D,L系统与R，S 系统的关系,D or L was originally derived from glyceraldehyde (+) or glyceraldehyde (-) Amino acids are normally chiral molecules with optical activity expressed by optical rotatory (+ or -) But D or L does not necessarily mean dextrorotatory (+) or levorotatory (

12、-) (D或L并不意味着该氨基酸右旋或左旋),Examples:,Brief summary小结：,Separation and analysis of amino acid mixture 氨基酸混合物的分离和分析,Mainly by Ion Exchange Chromatography (IEC) 主要通过离子交换色谱法来进行分离分析,Cation IEC/Elute with Na+ 阳离子交换色谱法/用Na+洗脱 Anion IEC/Elute with Cl- 阴离子交换色谱法/用Cl-洗脱,Detect AA by UV-VIS 用紫外-可见分光光度法进行检测,+,Gradient elution By Na+ solution 钠盐的梯度洗脱,Asp, Ser, Lys 在阳离子交换剂上的洗脱顺序：,1. Please solve problems 1-3, 9, 13-15 (p106) 2. Please calculate the pI for each amino acid in table 4.1 and write the values on a column added to that