生物化学教学课件：Nitrogen Fixation

1、手性单糖的名称中“D、L”，“+、-”, “、”表示单糖的什么性质？ 请写出L-葡萄糖的链状结构向环装结构转变的过程。青霉素和溶菌酶的抗菌作用机制各是什么？Aspirin, Ibuprofen等药物被称为非固醇类抗炎药物(NSAIDs)，它们的作用机理是什么？甘油磷脂的母体结构是什么？鞘脂的母体结构是什么？请写出它的化学结构式。甘油三脂和糖类都可以作为能量储存物质而存在，请说明他们在提供能量时有什么不同。请写出3-dAMP的化学结构DNA的Tm值是什么？它的大小与那些因素有关？固醇类和甲状腺素的作用机制是什么？为什么它们的作用比较慢（几小时到几天）？请简述激素作用的四个特点。Nitrogen

2、Fixation Nitrogen Fixation1 Nitrogen cycle 2 Nitrogen fixing organisms3 Biochemistry of nitrogen fixationMacroelement: C、H、O、N、P、S、K、Mg、Ca、Fe,Trace element:锌、锰、钠、氯、钼、硒、钴、铜、钨、镍 、硼等。Nitrogen ranks behind only carbon, hydrogen, and oxygen in its contribution. The mass of living systemsHCONAmino acids a

3、nd derivates NucleotidesVitamineNitrogen in human and animalHuman and animal can not fix the N2Microbes are intimately involved in nitrogen fixation Human and animal can not fix the N2大气中的N2 79%尿素及动植物遗体NO3-土壤中的微生物NH3NO3-氮素化肥The nitrogen cycle.Atmospheric fixation Biological fixation Industrial fixat

4、ion3CH4 + 6H2O - 3CO2 + 12H2 4N2+12H2 - 8NH3 high Temperature, High pressure)With the use of a catalystHuman are Changing Nitrogen CycleN化肥的种类Industrial FixationBiological Fixation轮 作第一期(年)豆類十字花科塊根莖類第二期(年)塊根莖類豆類十字花科第三期(年)十字花科塊根莖類豆類豆类 十字花科块根块茎类 块根块茎类 豆类十字花科十字花科块根块茎类 豆类123换茬：在同一块田地上一种作物收获以后换种另一种作物。重茬：

5、一种作物收获后接连种植同一种作物。Biological N2-fixing systems can thrive in soils poor in N. that they are a source of proteins, and that they provide N for soil /wairdocs/ilri/x5546e/x5546e05.htmBiological FixationThe ability to fix nitrogen is found only in certain bacteria. Some live in a symbiotic relationship

6、with plants of the legume familySome establish symbiotic relationships with plants other than legumesSome nitrogen-fixing bacteria live free in the soil. Nitrogen-fixing cyanobacteria藻青菌,蓝细菌are essential to maintaining the fertility of semi-aquatic environments like rice paddies稻, 谷,.Types of Biolog

7、ical Nitrogen FixationFree-living (asymbiotic)CyanobacteriaAzotobacter固氮(细)菌zutbktiSymbioticLegume-rhizobialegjum raizubiTypes of Biological Nitrogen FixationFree-living (asymbiotic) Cyanobacteria蓝细菌蓝藻1500多种，20多种具有固氮能力，水生植物，对水生农作物贡献重大蓝藻(Cyanobacteria)是原核生物，又叫蓝绿藻、蓝细菌；大多数蓝藻的细胞壁外面有胶质衣，因此又叫粘藻。单细胞，没有细胞核，

8、但细胞中央含有核物质，通常呈颗粒状或网状，染色质和色素均匀的分布在细胞质中。有的含有蓝藻叶黄素，有的含有胡萝卜素，有的含有蓝藻藻蓝素，也有的含有蓝藻藻红素。HeterocystNostoc commune, 普通念珠藻Free-living (asymbiotic)地木耳（真菌和蓝藻的共生）:普通念珠藻,固氮蓝藻,地皮菜 Types of Biological Nitrogen FixationFree-living (asymbiotic) Azotobacter 圆褐固氮菌自生固氮菌典型的自生固氮微生物，在土壤中能够独立进行固氮。杆菌或短杆菌，单生或对生。经过培养形成成对的菌体呈“8”字形

9、排列，并且外面有一层厚厚的荚膜。圆褐固氮菌具有较强的固氮能力，并且能够分泌生长素，促进植株的生长和果实的发育。Types of Biological Nitrogen FixationSymbioticSymbiotic Legume-RhizobiaAlder植桤木A few legumes (such as Sesbania田菁属rostrata rstreit, adj. 有喙的, 有喙状突起的) have stem nodules as well as root nodules. Stem nodules are capable of photosynthesis as well as

10、 nitrogen fixation.豌豆根瘤大豆根瘤Alder 植桤木and the other woody hosts of Frankia are typical pioneer species that invade nutrient-poor soils. These plants benefit from the nitrogen-fixing association, while supplying the bacterial symbiont共生有机体 with photosynthetic products.Legume-Rhizobium Symbiosis豆类根瘤菌Rhi

11、zobium raizubi The subfamilies of legumes , 700 genera, and 19,700 species of legumesOnly about 10% of the species have been evaluated for nodulation87% of which were nodulated ndjulet;Legume-Rhizobium SymbiosisRhizobium根瘤菌Gram -, rodMost studied symbiotic N2-fixing bacteriaNow subdivided into sever

12、al generaMany genes known that are involved in nodulation (nod, nol, noe genes)Specificity and effectiveness：A Rhizobium that nodulates cowpea may not nodulate Leucaena and vice versa. Rhizobium speciesHost plantsBradyrhizobium japanicumGlycine max (soybean)Rhizobium frediiGlycine max (soybean)R. ph

13、aseoliPhaseolus vulgaris (common bean)R. melilotiMedicago sativa (alfalfa)Melilotus sp. (sweet clovers)R. trifoliiTrifolium sp. (clovers)R. IeguminosarumPisum sativum (peas)Vicia faba (broad bean)Cowpea rhizobia group or Rhizobium sp.Vigna unguiculata (cowpea),Arachis hypogaea (peanut),Vigna subterr

14、anea (Bambara groundnut)Leucaena sp., Albizia sp.,Azarhizobium caulinodansSesbania sp. Sesbania rostrata (stem nodulating)Recognition between the microsymbiont and the host-plant have been suggested to explain specificity.Role of Root Exudates分泌液GeneralAmino sugars, sugarsSpecificFlavones黄酮(luteolin

15、毛地黄黄酮), isoflavones (genistein木黄酮), flavanones, chalcones查耳酮Inducers/repressors of nod genesVary by plant speciesResponsiveness varies by Rhizobia speciesRank of Biological Nitrogen FixationN2 fixing systemNitrogen Fixation (kg N/ha/year)Rhizobium-legume50 - 600Cyanobacteria- moss苔10 - 300Rhizospher

16、e根系 associations5 - 25Free- living0.1 - 25豌豆根瘤大豆根瘤Rhizobium Root NodulesFormation of a Root Nodule类似细菌体Bacteriods are shown in red, and peribacteriod membrane is is shown in blue.The nucleus is shown in yellow/green.Nodule MetabolismOxygen metabolismVariable diffusion barrierLegume-hemoglobinNitroge

17、n metabolismNH3 diffuses to cytosolAssimilationConversion to organic-N for transportCarbon metabolismFunctioning TCA in bacteroidsBiochemistry of Nitrogene FixationBiological nitrogen fixation requires a complex set of enzymes and a huge expenditure of ATP. Although the first stable product of the p

18、rocess is ammonia, this is quickly incorporated into protein and other organic nitrogen compounds.NitrogenaseNitrogen FixationAll nitrogen fixing bacteria use highly conserved enzyme complex called NitrogenaseNitrogenase is composed of of two subunits: an iron-sulfur protein a molybdenum-iron-sulfur

19、 proteinNitrogenase complexFeMo CofactorN2 + 8H+2NH3 + H28e-nitrogenasenitrogenase reductaseFd(red)Fd(ox)nMgATPnMgADP + nPiDimer of two identical subunits. Single 4Fe-4S redox centerOxidized and reduced by electron. Two binding sites for ATP/ADPTetramer with two copies of two different subunits, Con

20、tains both iron and molybdenum; Nitrogen fixation is carried out by a highly reduced form of dinitrogenase and requires eight electrons铁硫蛋白钼铁蛋白Steps in Nitrogen FixationNitrogenase:1 Nitrogenase: Two subunits, Exhangable of some subunit across species usually is not fully active as original2 Energy

21、consume3 Amonia is the product4 Inactivated by O2 5 Inhibited by NH3 6 Amonia Assimilation-carried by Glutamate and GlutamineAnaerobic chamberAnaerobic Culture MethodsGenetics of NitrogenaseGeneProperties and functionnifHnifDKnifAnifBnifENfixABCXfixKfixLJfixNOQPDinitrogenase reductaseDinitrogenaseRe

22、gulatory, activator of most nif and fix genesFeMo cofactor biosynthesisFeMo cofactor biosynthesisElectron transferRegulatoryRegulatory, two-component sensor/effectorElectron transferStructure genes and assembly-related geneRegulatoryNodule genesHost genes (Legume)固氮基因及其表达调控共生固氮-根瘤菌基因 结瘤基因nod 结瘤基因的调节基因,nodD 固氮基因nifHDK， fix植物基因 早期和晚期结瘤素基因生物固氮的基因工程1 Enhancing survival of nodule forming bacteriumExtend host range of crops, which can benefit from biological nitrogen fixation非豆科作物的改造Engineer microbes with high nitrogen fixing capacity现有固氮