Introduction to Biochemistry What is Biochemitry?Why importance? How to study Biochemistry? Demands in this lesson:

Biochemistry is to study the molecular basis of life. Why is it important and excited ?

1. the chemical or molecular basis of some central processes in biology are understood. 2. common molecular patterns and principles in diverse expressions of life. 3. biochemistry impact on medicine. 4. the development of biochemistry has enabled investigators to resolve the most challenging and fundamental problems in biology and medicine.

1. Active in class 2. Memory on the basic knowledge 3. Answer to the teacher’s question bravely and freely. 4. Not left too much after class 5. No need to preview, but review in time.

Introduction to protein structure and function Chapter I . Structure and function of proteins Introduction to protein structure and function 1. Enzymatic catalysis. 2. Transport and storage 3. Coordinated motion 4. Mechanical support. 5. Immune protection. 6.Generation and transmission of nerve impulses. 7.Control of growth and differentiation.

Chapter I . Structure and function of proteins (Part I) Main contents: Amino acids Peptides and polypeptides Determination of amino acid composition of proteins Determination of amino acid sequence of proteins

Chapter I . Structure and function of proteins 1. Amino Acids----The basic unit of proteins, and Polypeptide

(a)Amino acids have both acid and base properties (zwitterion). The structure of amino acids and their properties (a)Amino acids have both acid and base properties (zwitterion).

(b)Aromatic amino acids absorb light in the near-ultraviolet (c)All amino acids except glycine show asymmetry (d)Coloured by ninhydrin

Common structure formula of L-amino acids COOH R C H NH2 Common formula

Classification of amino acids 1. Apolar, hydrophobic R chain; 2. polar neutral (uncharged) ; 3. Acidic amino acid; 4. Basic amino acid.

Amino acids have both acid and base properties 1. Introduction to Henderson-Hasselbach equation (Conception of pH scale and water dissocation, acids dissociation)

2. A simple amino acids with a nonionizable R group gives a complex titration curve with two inflection points. 3. More complex amino acids with an ionizable R group show even more complex titration curves.

Aromatic amino acids absorb light in the near-ultraviolet phenylalanine, tyrosine, and typtophan Quiz: What importiance for this property of amino acids? What can you do applying this property?

All amino acids except glycine show asymmetry Chirality or handedness (take your hand as example) Stereoisomeric pair D: dextrorotatory; L: levorotatory All amino acids constructing proteins are L form. Some D-amino acids: in bacterial cell walls and certain antibiotics.

2. Peptides an polypeptides peptide bond: partial double-bond character not rotated freely Amide plane and amide unit polypeptides chain Conception of polypeptides or oligopeptides: other bond in proteins or polypeptides

Peptides: Short polypeptides chains, up to length of about 20 amino acids, are called peptides; However if they are fragments of whole polypeptide chains, we call it oligopeptides.

3. Determination of amino acid composition of proteins(step?) A. Break down the polypeptide chain into AAs. B. Separate the free AAs. C. Measure the quantities of each amino acids.

Free amino acids are coloured by ninhydrin (Reaction) R-C-COOH + 2 O NH2 OH C H C OH O

Free amino acids are coloured by ninhydrin (Production) Ninhydrin coloured by red

Structure and function of proteins Part II .The Three-Dimensional Structure of Proteins Contain: (1)Primary structure (2)secondary structure -helix; -pleated sheet -blend(turn); random coil one special structure: motif (eg.Zinc finger)

(3) Tertiary structure special structure: domain (4) Quaternary structure subunit

(5) Bonds in the protein structure (6) Relationship of structure

Domain

Globular proteins

Section 4 the physic and chemical character of protein and isolation and purification of protein

4. Determination of amino acids sequence of proteins (steps?) (1) purification of protein; (2)cleavage of all disulfide bonds (3)determination of the terminal amino acid residues (4)specific cleavage of polypeptide chain into small fragments in at least two different cleavage methods.

(5) Independent separation and sequence determination of peptides produced by the different cleavage methods. (6) Reassembly of the individual peptides with appropriate overlaps to determine the overall sequence.

选择题练习 蛋白质化学

1. 下列含有两个羧基的氨基酸是( ) A 精氨酸 B 赖氨酸 C 甘氨酸 D 色氨酸 E 谷氨酸

2. 多肽链中主连骨架的组成是( ) A -NCCNNCCNNCCN- B -CHNOCHNOCHNO- C -CONHCHCONHC- D -CNOHCNOHCNOH- E -CNHOCNHOCNHO-

3. 关于肽键的特点哪项叙述是不正确的? A 肽键中的C-N键比相邻的N-C键短 B 肽键的C-N键具有部分双键性质 C 与碳原子相连的N和C所形成的化 学键可以自由旋转 D 肽键的C-N键可以自由旋转 E 肽键中的C-N键所连的四个原子在同 一平面上

4. 蛋白质中的螺旋与折叠都属于( ) A 一级结构 B 二级结构 C 三级结构 D 四级结构 E 侧链结构

5. 关于螺旋的论述哪一项是不正确的? A 螺旋是二级结构的常见形式 B 多肽链的盘绕方式是右手螺旋 C 每3.6个氨基酸残基盘绕一圈 D 其稳定性靠相邻的肽键平面间形成的氢键 E 影响螺旋地因素是氨基酸残基侧链的结构与性质

6. 关于蛋白质结构的论述哪项是正确的? A 一级结构决定二、三级结构 B 二、三级结构决定四结构 C 三级结构都具有生物学活性 D 四级结构才具有生物学活性 E 无规则卷曲是在二级结构的基础上盘曲而成

7. 蛋白质分子引起280nm 光吸收的主要成分是( ) A 丝氨酸的-OH B 半胱氨酸的-SH C 苯丙氨酸的苯环 D 色氨酸的吲哚环 E 组氨酸的咪唑环

8. 下列哪种氨基酸溶于水时不引起偏振光旋转? A 谷氨酸 B 亮氨酸 C 丙氨酸 D 甘氨酸 E 苯丙氨酸

9. 蛋白质变性是由于( ) A 一级结构改变 B 辅基地脱落 C 亚基解聚 D 蛋白质水解 E 空间构象改变

10. 蛋白质水解产物在pH6.0时,用阳离子交换剂层析时,第一个被洗脱下来的氨基酸是( ) A Val(pI5.96) B Asp(pI2.77) C Lys(pI9.74) D Arg(pI10.76) E Tyr(pI5.66)

11. Glycine, pK-COOH = 2.34, pK-NH2 = 9.60, its pI is ( ) A 11.94 B 7.26 C 5.97 D 3.63 E 2.34

12. The unit composition of protein is ( ) A L--amino acids B D--amino acids C L--amino acids D D--amino acids E L,D--amino acids

13. The main chemical bond which maintain quaternary structure of protein is ( ) A hydrogen bond B salt bond C hydrophobic bond D disulfide bond E van der waals force

14. In which solution, does serum albumin,pI 4.7, positively charge? A pH4.0 B pH5.0 C pH6.0 D pH7.0 E pH8.0

15. 蛋白质特异的生物学功能主要有( ) A 是各种组织的基本组成成分 B 催化功能 C 收缩及运动功能 D 免疫功能 E 调节功能

16. 下列关于折叠结构的论述那些是正确的? A 是一种伸展的肽链结构 B 肽键平面折叠成锯齿状 C 两条以上的多肽链可顺向或反向平行 D 两条链间聚合力维持其稳定 E R基团交替分布在片层的上下方