食品酶學(xué)總復(fù)習(xí)2013課件

1、食品酶學(xué)總復(fù)習(xí)一、單項(xiàng)選擇題（中英文出題102=20）二、名詞解釋（英文出題,英文作答 54=20）三、判斷題（英文出題102= 20）四、問答題（中文出題 83= 24 ）五、綜合分析題（中文出題 116= 16） 食品酶學(xué)考試題型1、Characteristics of enzymeEnzymes have extraordinary catalytic power, often far greater than those non-biological catalysts.Enzymes often have a high degree of specificity for their

2、substrates.Enzymes are often regulated.Enzymes usually work under very mild conditions of temperature and pH.一、選擇題要點(diǎn) 2、Specificity In general, there are four distinct types of specificity:A- Absolute specificity - the enzyme will catalyze only one reaction.B- Group specificity - the enzyme will act

3、only on molecules that have specific functional groups, such as amino, phosphate and methyl groups.C- Linkage specificity - the enzyme will act on a particular type of chemical bond regardless of the rest of the molecular structure.D- Stereochemical specificity - the enzyme will act on a particular

4、steric or optical isomer (旋光異構(gòu)體).3、Enzymes are classified into six major groups defined by the reaction that they catalyze. (1) Oxidoreductases(2) Transferases(3) Hydrolases(4) Lyases(5) Isomerases(6) Ligases, synthetasesOTHLIL六大類酶的記憶訣竅：口訣：O2 + H2 H2O 氧轉(zhuǎn)水，裂異合。氧化還原酶 轉(zhuǎn)移酶 水解酶 裂解酶 異構(gòu)酶合成酶4、International

5、classification of enzymesClass Name Type of reaction catalyzed Example 1 Oxidoreductases Transfer of electrons A-+BA+B- alcohol dehydrogenase2 Transferases Transfer of functional groups Hexokinase A-B + C A + B-C 3 Hydrolases Hydrolysis reactions Trypsin A-B + H2O A-H + B-OH 4 Lyases Cleavage of C-C

6、, C-O, C-N Pyruvate decar- and other bonds, often forming boxylase a double bond A-B A=B + X-Y5 Isomerases Transfer of groups within a molecule Maleate A-B A-B isomerase6 Ligases Bond formation coupled Pyruvate or synthases to ATP hydrolysis carboxylase A + B A-B XYXYXY丙酮酸脫羧化酶 馬來酸異構(gòu)酶丙酮酸羧化酶 5、What is

7、 velocity of enzyme?Enzyme velocity are normally reported as values at time zero ( symbol V0; mol min-1)In fact, V0 means the rate of an enzyme-catalyzed reaction at beginning of reaction.Why V0 should be used to represent an enzyme activity?The substrate conc is highest.No feedback inhibition by pr

8、oduct.Enzyme activity is in best state.7、Enzyme Inhibition (Mechanism)CompetitiveNon-competitiveUncompetitiveEEDifferent siteCompete for active siteInhibitorSubstrateCartoon GuideEquation and DescriptionI binds to free E only,and competes with S;increasing S overcomesInhibition by I. I binds to free

9、 E or ES complex; Increasing S cannot overcome I inhibition.I binds to ES complex only, increasing S favorsthe inhibition by I.E + S ES E + P + IEI E + S ES E + P + + I I EI + S EIS E + S ES E + P + I EIS XJuang RH (2004) BCbasicsKmEnzyme Inhibition (Plots)CompetitiveNon-competitiveUncompetitive Dir

10、ect PlotsDouble ReciprocalVmaxVmaxKmKmS, mMvoS, mMvoIIKmS, mMVmaxIKmVmaxVmaxVmax unchangedKm increasedVmax decreasedKm unchangedBoth Vmax & Km decreasedI1/S1/Km1/vo1/ VmaxITwo parallellinesIIntersect at X axis1/vo1/ Vmax1/S1/Km1/S1/Km1/ Vmax1/vo Intersect at Y axis= Km練習(xí)P381:5 Making RNA from a DNA

11、template to transfer information from the genome IngredientsrNTPs（ribonucleotides, substrate）DNA templateRNA polymerase 8、Transcription 轉(zhuǎn)錄核苷酸 以DNA為模板，以核苷三磷酸為底物，在RNA聚合酶（轉(zhuǎn)錄酶）的作用下，生成RNA分子的過程。 10、沉淀分離方法沉淀分離法分離原理鹽析沉淀法利用不同蛋白質(zhì)在不同的鹽濃度條件下溶解度不同的特性，通過在酶液中添加一定濃度的中性鹽，使酶或雜質(zhì)從溶液中析出沉淀，從而使酶與雜質(zhì)分離等電點(diǎn)沉淀法利用兩性電解質(zhì)在等電點(diǎn)時(shí)溶解度最

12、低，以及不同的兩性電解質(zhì)有不同的等電點(diǎn)這一特性，通過調(diào)節(jié)溶液的pH值，使酶或雜質(zhì)沉淀析出，從而使酶與雜質(zhì)分離有機(jī)溶劑沉淀法利用酶與其他雜質(zhì)在有機(jī)溶劑中的溶解度不同，通過添加一定量的某種有機(jī)溶劑，使酶或雜質(zhì)沉淀析出，從而使酶與雜質(zhì)分離復(fù)合沉淀法在酶液中加入某些物質(zhì)，使它與酶形成復(fù)合物而沉淀下來，從而使酶與雜質(zhì)分離選擇性變性沉淀法選擇一定的條件使酶液中存在的某些雜質(zhì)變性沉淀，而不斷影響所需的酶，從而使酶與雜質(zhì)分離 層析方法分離依據(jù)吸附層析利用吸附劑對(duì)不同物質(zhì)的吸附力不同而使混合物中各組分分離分配層析利用各組分在兩相中的分配系數(shù)不同，而使各組分分離離子交換層析利用離子交換劑上的可解離基團(tuán)（活性基團(tuán)）

13、對(duì)各種離子的親和力不同而達(dá)到分離目的凝膠層析以各種多孔凝膠為固定相，利用流動(dòng)相中所含各種組分的相對(duì)分子質(zhì)量不同而達(dá)到物質(zhì)分離親和層析利用生物分子與配基之間所具有的專一而又可逆的親和力，使生物分子分離純化層析聚焦將酶等兩性物質(zhì)的等電點(diǎn)特性與離子交換層析的特性結(jié)合在一起，實(shí)現(xiàn)組分分離CharacteristicCarrier Binding MethodsCross-linking MethodEntrapping MethodPhysical adsorptionIonic Binding Covalent BindingPreparationEasyEasyDifficultDifficult

14、DifficultEnzyme ActivityLowHighHighModerateHighSubstrate SpecificityUnchangeableUnchangeableChangeableChangeableUnchangeableBinding ForceWeakModerateStrongStrongStrongRegenerationPossiblePossibleImpossibleImpossibleImpossibleGeneral ApplicationLowModerateModerateLowHighCost of ImmobilizationLowLowHi

15、ghModerateLow12、Comparison of the characteristics of different methods of enzyme immobilization13、有機(jī)溶劑的選擇有機(jī)劑的極性要選擇恰當(dāng)：極性過強(qiáng),奪取較多酶表面水分子,使疏水性底物溶解度降低;極性過弱,底物難以進(jìn)入必需水層;故取中間: 2lgP514、酶促反應(yīng)的有機(jī)介質(zhì)體系1、含微量水的有機(jī)溶劑單相體系；2、與水混溶的有機(jī)溶劑和水形成的單相體系；3、水與有機(jī)溶劑形成的兩相或多相體系：4、反相膠束體系； 不管采用何種有機(jī)介質(zhì)反應(yīng)體系，酶催化反應(yīng)的介質(zhì)中都含有機(jī)溶劑和一定量的水。它們都對(duì)催化反應(yīng)有顯著

16、的影響。 15、 雜合酶的制備方法 雜合酶的構(gòu)建方法是DNA水平的基礎(chǔ)操作和酶學(xué)檢測方法的結(jié)合，其實(shí)質(zhì)是突變（組裝）和篩選。 在進(jìn)化過程中，把來自不同酶分子的（亞）結(jié)構(gòu)域進(jìn)行組裝成為一個(gè)新的單一結(jié)構(gòu)域，或者把來自不同酶的本身沒有活性的模塊重組起來，同時(shí)在一個(gè)進(jìn)化體系中篩選，就可能獲得比親本功能具有更高效率的、或者衍生出新功能的子代重組體。所謂模擬酶就是利用有機(jī)化學(xué)的方法合成一些比酶簡單的非蛋白質(zhì)分子，可以模擬酶對(duì)底物的絡(luò)合和催化過程，既可達(dá)到酶催化的高效性，又可以克服酶的不穩(wěn)定性。16、模擬酶的概念自從2002年4月瑞典斯德哥爾摩大學(xué)Margareta Tornqvist教授首次發(fā)現(xiàn)，在油炸或

17、焙烤的馬鈴薯和谷物類食品中存在具有神經(jīng)毒性的潛在致癌物丙烯酰胺，有關(guān)丙烯酰胺的問題立即引起了全世界的廣泛關(guān)注。隨后英國、美國、加拿大等發(fā)達(dá)國家也開展了相關(guān)研究。許多國家和國際性機(jī)構(gòu)對(duì)丙烯酰胺在食品中形成機(jī)理、危害評(píng)估和消除方法等方面進(jìn)行廣泛而深入研究。17、降低淀粉類食品高溫產(chǎn)生丙烯酰胺含量1.保持混濁果汁穩(wěn)定性（番茄汁、番茄醬）2.生產(chǎn)澄清果汁 3.提高果汁榨汁率4.加工水果罐頭5.防止果汁混濁 1.破壞果膠酶2.應(yīng)用果膠酶3.應(yīng)用果膠酶4.破壞果膠酶5.應(yīng)用果膠酶18、果膠酶的應(yīng)用 1. enzyme: Biological catalysts that promote and speed

18、 up chemical reactions without themselves being altered (consumed) in the process. 2. induced-fit hypothesis: When an enzyme approaches to its substrate mutually, the structure of enzyme could be changed and adapted each other, then combines with the substrate.3. active site: The region of the enzym

19、e that can binds the substrate, to form an enzyme-substrate complex, and transforms it into product.4. Vmax: The velocity of enzyme-catalytic reaction when enzyme is completely saturated, directly proportional to the concentration of enzyme.5. zymogen: Some enzymes are synthesized and secreted as la

20、rge inactive precursors before exert their catalytic activity. 二、名詞解釋要點(diǎn)1、The specificity of a reaction decided by apoenzyme. The sort and character of a reaction decided by cofactor.2、Combine with apoenzyme loosely, the coenzyme could be removed by ultrafiltration or dialysis. However, combine with

21、apoenzyme tightly through covalent bonds , the prosthetic group couldnt be removed by ultrafiltration or dialysis.3、The active site is a three-dimensional entity, often a cleft or crevice on the surface of the protein, in which the substrate is bound by multiple weak interactions.4、Isozymes are a gr

22、oup of enzymes, which catalyze the same reaction, but have different protein structure, physicochemical and immunological properties.三、判斷題要點(diǎn)5、Small allosteric effectors binding to allosteric site of the enzyme by non-covalent bonds triggers changes in enzyme conformation, then alters the catalytic a

23、ctivity of the enzyme.6、The allosteric regulation is that the allosteric effectors non-covalently bind to the enzyme and change its conformation and activity, whereas the covalent modification is that other enzymes covalently modify the enzyme and alter its structure and activity.7、Zymogens are acti

24、vated by the irreversible hydrolysis of one or more peptide bonds and forming or exposing the active site in the enzyme molecule. 8、Heterotrophic microbe is an organism that must obtain its carbon in an organic form. Autotrophic microbe is an organism that uses CO2, an inorganic gas, as its carbon s

25、ource. 9、The more concentrated the protein the more it interacts with itself in the crystallization solution and can form crystals. 10、Specific activity should increases throughout the purification, reaching a maximum value when the protein is pure. While the activity should decreases through the pu

26、rification, and in a long purification the final yield may be only a few percent.11、Non-aqueous medium refers to all of the media whose main component is not water. 12、One of the advantages of biocatalysts in non-aqueous system is increasing the solubility of compounds with high hydrophobicity. 13、A

27、n artificial enzyme is a synthetic, organic molecule prepared to recreate the active site of an enzyme. 14、A protease is any enzyme that performs proteolysis, that is, begins protein catabolism by hydrolysis of the peptide bonds that link amino acids together in the polypeptide chain forming the pro

28、tein. 15、Many ribozymes are catalytic, and some such as self-cleaving ribozymes are consumed by their reactions. 16、The bromelain, ficin, or papain can be used as meat tenderizer. 17、Amylase is an enzyme that catalyses the hydrolysis of starch into sugars.18、The ability to digest milk was limited to

29、 children as adults did not produce lactase, an enzyme necessary for digesting the lactose in milk.19、Carbon sources can not only provide the carbon element, but also provide the energy for microbes.20、The substance couldnt be utilized by generic species, but could be utilized by microbes. 四、問答題1、酶

30、分 子 修 飾Types of enzyme modificationMetal ion substitute modification *Macromolecules combine modification *Side residues modification *Affinity modificationPeptide chain limit hydrolysis modification *Nucleotide chain cleavage modificationAmino-acid substitute modificationNucleotide substitute modif

31、icationPhysical modificationEnzyme directed evolution金屬離子置換修飾、大分子結(jié)合修飾、側(cè)鏈殘基修飾、親和修飾、肽鏈有限水解修飾、核苷酸鏈剪切修飾、氨基酸置換修飾、核苷酸置換修飾、物理修飾、酶定向進(jìn)化等。 2、酶分子的物理修飾物理修飾的概念通過各種物理方法，使酶分子的空間構(gòu)象發(fā)生某些改變，從而改變酶的某些特性和功能的方法物理修飾的特點(diǎn)不改變酶的組成單位及其基團(tuán)酶分子中的共價(jià)鍵不發(fā)生改變 酶的一級(jí)結(jié)構(gòu)不變副鍵發(fā)生某些改變和重排 酶的高級(jí)結(jié)構(gòu)發(fā)生變化（1）酶在水溶液中以自由的游離狀態(tài)存在，但固定后酶分子便從游離的狀態(tài)變?yōu)槔喂痰亟Y(jié)合于載體的狀態(tài)；（

32、2）固定化酶的活力在多數(shù)情況下比天然酶的活力低；（3）固定化酶的穩(wěn)定性（熱穩(wěn)定性、操作穩(wěn)定性、酸堿穩(wěn)定性等）一般都比游離酶提高得多；（4）產(chǎn)物為酸性時(shí)固定化酶的最適pH比游離酶的最適pH高一些；反之，產(chǎn)物為堿性時(shí)，固定化酶的最適pH比游離酶的pH為低。（5）固定化酶的底物特異性與底物分子量的大小有一定關(guān)系，大分子底物由于載體引起的空間位阻作用，難以與酶分子接近而無法進(jìn)行催化反應(yīng)；（6）固定化酶的最適反應(yīng)溫度多數(shù)較游離酶高；（7）固定化酶蛋白分子的高級(jí)結(jié)構(gòu)的變化以及載體電荷的影響可導(dǎo)致底物和酶的親合力的變化。3、酶被固定化后理化性質(zhì)的變化4、水在非水相反應(yīng)體系中對(duì)酶催化反應(yīng)的影響1）酶都溶于水，

33、只有在一定量的水存在的條件下，酶分子才能進(jìn)行催化反應(yīng)。所以酶在有機(jī)介質(zhì)中進(jìn)行催化反應(yīng)時(shí)，水是不可缺少的成分之一。有機(jī)介質(zhì)中的水含量多少對(duì)酶的空間構(gòu)象、酶的催化活性、酶的穩(wěn)定性、酶的催化反應(yīng)速度等都有密切關(guān)系，水還與酶催化作用的底物和反應(yīng)產(chǎn)物的溶解度有關(guān)。2）酶分子只有在空間構(gòu)象完整的狀態(tài)下，才具有催化功能。在無水的條件下，酶的空間構(gòu)象被破壞，酶將變性失活。故此，酶分子需要一層水化層，以維持其完整的空間構(gòu)象。維持酶分子完整的空間構(gòu)象所必需的最低水量稱為必需水。 3）有機(jī)介質(zhì)中水的含量對(duì)酶催化反應(yīng)速度有顯著影響。存在最適水含量。 酶是具有催化功能的生物大分子，即生物催化劑，包含蛋白質(zhì)酶和核酶。1）

34、蛋白質(zhì)酶的一級(jí)結(jié)構(gòu)比核酶復(fù)雜 蛋白質(zhì)酶是由20多種不同的氨基酸組成的多肽聚合物，而核酶是由4種核苷酸組成的聚合物。2）幾個(gè)氨基酸可以形成1個(gè)蛋白質(zhì)酶的三維結(jié)構(gòu)，且蛋白質(zhì)酶的活性中心具有剛性，由4種核苷酸組成的核酶不具蛋白質(zhì)酶的這些特性。3）核酶需要較大的結(jié)構(gòu)才能提供較穩(wěn)定的活性中心，從而有效地提高反應(yīng)速率，小的核酶結(jié)構(gòu)只能勉強(qiáng)滿足催化反應(yīng)的要求。5、Comparison of ribozyme and protein enzyme in structure 原理步驟： 6、 分子印跡技術(shù)（MIT）是指為獲得在空間、結(jié)構(gòu)和結(jié)合位點(diǎn)上與某一分子（印跡分子）完全匹配的聚合物的實(shí)驗(yàn)制備技術(shù)。 （1）在一定溶劑中，膜板分子（Template Molecular，即印跡分子）與功能單體（Functional Monomer）依靠官能團(tuán)之間的共價(jià)或非共價(jià)作用形成主客體配合物-兩者的互補(bǔ)反應(yīng)（2）加入交聯(lián)劑（Cross linker），通過引發(fā)劑引發(fā)進(jìn)行光或熱聚合，使主客體配合物與交聯(lián)劑通過自由基共聚合在膜板分子周圍形成高交聯(lián)的剛性聚合物。-聚合反應(yīng)（3）將聚合物中的印