动物的的变态

变态是动物学中一个较重要的专用名词,有关内容在中学课本也多处涉及到。现择要介绍一点动物变态的知识,供动物学教学参考。何谓动物的变态动物由于外在和内在的原因,个体形态发生变化,这叫变态。但动物学所讲的变态,是狭义地从发生学角度理解,即胚胎不直接转变为成体,而是在后期发育过程中,先形成形态、生理、生态方面特殊的幼体,行独立生活和生长,以后在某阶段发生急剧变化,转变为成体。青     

活的不可培养的细菌的研究进展

活的不可培养微生物(VBNC)即一些微生物明显地丧失了可培养的特性,但是保留了自身原有的代谢活力,并且在一定条件下,又可以回复到可培养的状态。从VBNC细菌的诱导条件、生物学特性和检测方法3个方面对VBNC细菌研究进展做一综述。     

高频率的波动对于种子的萌发和植物的发育的影响

本文主要是以理论和试验来说明音波对植物的生长发育和种子萌发所起的影响。在农业实践上音波所起的作用,据现在所知:有缩短植物成熟期,加速萌芽和增强植物的生长发育等。这一些非但具有理论和实践上的意义,同时在今後把物理科学应用到农业科学中开辟了极广阔的前程。     

真核细胞的基因的组织

一、真核细胞基因的基本结构 1.转录单位: 从已知的数十种基因的顺序,可得出一个具有功能的基因的共同规律,在基因5’端-25至-75区,有CCAAT和TATAAA区(后者又称ATA box或Hogness box),相当于促进子区(Promotor),为体外转录所必需。     

由吸附的缩氨酸诱导的细胞膜的形变

研究了由一系列相互平行的吸附在细胞膜上的缩氨酸引起的膜的弹性形变,以及膜对缩氨酸的包裹行为,得到膜的平衡方程,用它可以来处理大尺度的形变,弯曲能量、吸附能量和弹性形变的相互竞争导致膜对缩氨酸发生从不吸附到部分吸附乃至完全包裹的结构转变．在膜的形变很小的时候,可以得到系统能量的解析解。     

远古的人们是怎样认识自己的起源的

人是从那里来的? 回答这个问题,你也许会说这有什么困难——人是从古猿变来的;甚至你还会进一步说,在这个从猿到人的转变过程中,劳动起着决定性的作用。然而这个现在看来比较明了的道理,恰是经历了多么漫长的认识过程才达到的呵!现在让我们首先来谈谈,远古的人们是怎样认识自己的起源的。最初的原始人可能还想不到自己的起源在人类诞生的最早时期,“最初的、从动物界分离出来的人,在一切本质方面是和动物本身一样不自由的”(恩格斯:《反杜林论》),这些最初的原始人为艰苦     

敲除pckA基因的结核杆菌引起的免疫反应的研究

研究结核杆菌pckA基因编码的磷酸烯醇型丙酮酸羧激酶(PEPCK)诱导机体产生的保护性免疫反应。用敲除pckA基因的牛结核杆菌BCG和野生型BCG分别感染小鼠,取肝、肺、脾进行病理分析,并进行脾细胞培养,检测CD4 、CD4 /CD8 、细胞因子IFNI-γI、L-12和TNF等。用敲除pckA基因的BCG感染的小鼠比野生型BCG感染的小鼠体内产生的结核结节少且不典型,炎性程度低。野生型BCG感染的小鼠脾脏内的CD4 T细胞和CD4 /CD8 、细胞因子IFN-γ、IL-12、TNF均明显高于敲除pckA基因BCG感染的小鼠。pckA基因为结核杆菌生长所必需,其编码产物PEPCK能够刺激机体产生免疫反应,是一种很好的疫苗候选分子。     

分离的蚕豆细胞核的RNA聚合酶活力的研究

利用Triton X-100对叶绿体膜的作用,可快速地从蚕豆幼叶制备较纯净的细胞核,它具有较高的RNA聚合酶活力。比较了两种分离核的方法,证明利用匀浆法制备的核具有较高的活力。核活力与发育时期有关系,茎端和第1对幼叶的核活力显著高于第2和第3对叶片的核活力。此外,核活力明显地受反应液内锰离子的抑制。     

正红菇的化学成分的研究

采用ＧＣ、ＨＰＬＣ、ＧＣ／ＭＳ．凝胶过滤层析等方法对正红菇（Ｒｕｓｓｕｌａ ｖｉｎｏｓａ）的某些成分的分析结果表明：正红菇其色素由红紫色素和黄色素两个组分的组成,其中红紫色素对酸稳定,对碱及高温不稳定,而黄色素对它们则表现一定的稳定性。其多糖含量２．７４％,含有五种多糖组分。在脂肪酸组成上,主要是油酸和亚油酸,并有可能 存在ＥＰＡ和ＤＨＡ。全氨基酸分析表明含有十六种氨基酸,必需氨基酸占总氨基酸的５     

Role of metal ion-mediated interactions in the assembly and stability of Sesbania mosaic virus T=3 and T=1 capsids

Sesbania mosaic virus (SeMV) capsids are stabilized by RNA-protein, protein-protein and calcium-mediated protein-protein interactions. The removal of calcium has been proposed to be a prerequisite for the disassembly of the virus. The crystal structure of native T=3 SeMV capsid revealed that residues D146 and D149 from one subunit and Y205, N267 and N268 of the neighboring subunit form the calcium-binding site (CBS). The CBS environment is found to be identical even in the recombinant CP-NDelta65 T=1 capsids. Here, we have addressed the role of calcium and the residues involved in calcium co-ordination in the assembly and stability of T=3 and T=1 capsids by mutational analysis. Deletion of N267 and N268 did not affect T=3 or T=1 assembly, although the capsids were devoid of calcium, suggesting that assembly does not require calcium ions. However, the stability of the capsids was reduced drastically. Site-directed mutagenesis revealed that either a single mutation (D149N) or a double mutation (D146N-D149N) of SeMV coat protein affected drastically both the assembly and stability of T=3 capsids. On the other hand, the D146N-D149N mutation in CP-NDelta65 did not affect the assembly of T=1 capsid, although their stability was reduced considerably. Since the major difference between the T=3 and T=1 capsids is the absence of the N-terminal arginine-rich motif (N-ARM) and the beta-annulus from the subunits forming the T=1 capsids, it is possible that D149 initiates the N-ARM-RNA interactions that lead to the formation of the beta-annulus, which is essential for T=3 capsid assembly.     

Stability constants of thiocyanato complexes of cobalt(II), nickel(II) and copper(II) in methanol.

A spectrophotometric study of cobalt(II), nickel(II) and copper(II) thiocyanato complexes was carried out in methanol at 25 degrees C and at a constant ionic strength of 1 M. Under the experimental conditions, two mononuclear complexes are identified with each of the three metal ions. Their stability constants are determined with a recent PC program SIRKO and the calculated values are: for cobalt, log beta 1 = 1.6, log beta 2 = 2.7; for nickel, log beta 1 = 1.8, log beta 2 = 3.0; and for copper, log beta 1 = 3.0, log beta 2 = 3.6.     

The stoichiometry and stability of the NADP complexes with manganese(II) ions as studied by electron paramagnetic resonance.

Magnetic resonance techniques have been applied to study the stability of the complexes formed between Mn(II) ions and NADP in aqueous solutions at a pH of 7.5 and 20 degrees C. The electron paramagnetic resonance (epr) data indicate that at low Mn(II) ion concentrations ([Mn(II)] less than 1 mM; [NADP] approximately 5 mM), a 1:1 complex is formed with an apparent stability constant K1 = 370 +/- 50 M-1 at an ionic strength of 0.22 in the presence of 0.20 M Cl-. At high Mn(II) ion concentrations, a Mn(II)2-NADP species, with an apparent stability constant K2 = 54 +/- 17 M-1, is present in significant amounts. When the epr data are corrected for the presence of the MnCl+ ion, the analysis of the new Scatchard plot yields stability constants for the two sites of K1 = 640 +/- 90 M-1 and K2 = 88 +/- 13 M-1, respectively. The presence of two metal ion binding sites on the NADP molecule has not been observed previously, and previous workers have always analyzed their data in terms of the 1:1 Mn(II)-NADP complex. An epr temperature study of K1 yields a value of delta H equal to 1.3 +/- 0.2 kcal/mol (1 cal = 4.187 J).     

Thermodynamics of ribonuclease T1 denaturation.

Differential scanning calorimetry has been used to investigate the thermodynamics of denaturation of ribonuclease T1 as a function of pH over the pH range 2-10, and as a function of NaCl and MgCl2 concentration. At pH 7 in 30 mM PIPES buffer, the thermodynamic parameters are as follows: melting temperature, T1/2 = 48.9 +/- 0.1 degrees C; enthalpy change, delta H = 95.5 +/- 0.9 kcal mol-1; heat capacity change, delta Cp = 1.59 kcal mol-1 K-1; free energy change at 25 degrees C, delta G degrees (25 degrees C) = 5.6 kcal mol-1. Both T1/2 = 56.5 degrees C and delta H = 106.1 kcal mol-1 are maximal near pH 5. The conformational stability of ribonuclease T1 is increased by 3.0 kcal/mol in the presence of 0.6 M NaCl or 0.3 M MgCl2. This stabilization results mainly from the preferential binding of cations to the folded conformation of the protein. The estimates of the conformational stability of ribonuclease T1 from differential scanning calorimetry are shown to be in remarkably good agreement with estimates derived from an analysis of urea denaturation curves.     

葛根素配位特性研究

本文运用配位化学的基本原理,采用pH电位滴定法,对葛根素的配位特性进行研究。结果表明在碱性条件下,葛根素结构易发生改变。在25℃和37℃,葛根素能和铜离子、锌离子、铁离子、铝离子、钙离子形成配合物。计算得出葛根素与Cu2 、Ca2 、Zn2 、Al3 、Fe2 的络合稳定常数lgK分别为3.28、2.16和1.12、2.85和1.72、2.78和1.63、2.94和1.87。     

Sequestration of biogenic amines by alginic and fulvic acids

The interaction of natural (alginic and fulvic acids) and synthetic (polyacrylic acid 2.0 kDa) polyelectrolytes with some protonated polyamines [diamines: ethylendiamine, 1,4-diaminobutane (or putrescine), 1,5-diaminopentane (or cadaverine); triamines: N-(3-aminopropyl)-1,4-diaminobutane (or spermidine), diethylenetriamine; tetramine: N,N'-bis(3-aminopropyl)-1,4-diaminobutane (or spermine); pentamine: tetraethylene-pentamine; hexamine: pentaethylenehexamine] was studied at T=25 degrees C by potentiometry and calorimetry. Measurements were performed without supporting electrolyte, in order to avoid interference, and results were reported at I=0 mol L(-)(1). For all the systems, the formation of (am)L(2)H(i) species was found (am=amine; L=polyelectrolyte; i=1...4, depending on the amine considered). The stability of polyanion-polyammonium cation complexes is always significant, and for high-charged polycations, we observe a stability comparable to that of strong metal complexes. For example, by considering the formation reaction (am)H(i)+2L=(am)L(2)H(i) we found log K(i)=6.0, 6.5 and 10.8 for i=1, 2 and 3, respectively, in the system alginate-spermidine. Low and positive formation DeltaH(degrees) values indicate that the main contribution to the stability is entropic in nature. The sequestering ability of polyelectrolytes toward amines was modelled by a sigmoid Boltzman type equation. Some empirical relationships between stability, charges and DeltaG(degrees) and TDeltaS(degrees) are reported. Mean values per salt bridge of formation thermodynamic parameters (DeltaX(degrees) (n)) are DeltaG(degrees) (n)=-5.8+/-0.4, DeltaH degrees (n)=0.7+/-0.5 and TDeltaS(degrees) (n)=6.5+/-0.5 kJmol(-)(1) for all the systems studied in this work.     

Mixed Chelates of Ca(II)-Pyridine-2,6-Dicarboxylate with Some Amino Acids Related to Bacterial Spores

The high resistance of bacterial spores to heat has been repeatedly postulated to be due to stabilization of spore biopolymers by metal chelate compounds. Binding of calcium dipicolinic acid (Ca(II)-DPA) with spore proteins and amino acids has been discussed in the literature, but equilibrium data are generally lacking. By means of potentiometric pH titrations at 25 degrees C and an ionic strength of 1.0 (KNO(3)), the formation of Ca(II)-DPA (1:1 and 1:2) chelates and the interactions of Ca(II)-DPA chelate with a mole of each of three typical amino acids viz., cysteine, alanine, and glycine has been investigated. Analysis of the potentiometric data indicates that calcium and DPA forms 1:1 and 1:2 chelates with log K(ML1) = 4.39 +/- 0.01 and log K(ML2) = 2.25 +/- 0.01. In the presence of an equimolar amount of each of the amino acids under consideration, the Ca(II)-DPA chelate forms mixed ligand (ternary) chelate yielding the following stepwise stability constants: log K(1) = 4.17 +/- 0.01, log K(2) = 0.78 +/- 0.01 for cysteine, log K(1) = 4.06 +/- 0.01, log K(2) = 0.65 +/- 0.01 for alanine, and log K(1) = 4.30 +/- 0.02, log K(2) = 0.11 +/- 0.01 for glycine. Methods for calculating the stability constants of the mixed ligand system have been developed. On the basis of the potentiometric equilibrium data, possible structures for the various calcium chelate species are discussed. The data suggest that the differences in heat resistance of various strains of bacterial spores may conceivably be related to the differences in composition and stability of coordination complexes in the spore.     

Topological diversity of artificial beta-barrels in water

Rigid-rod beta-barrels are composed of interdigitating, short, amphiphilic peptide strands flanked by stabilizing rigid-rod "staves". We here report studies on the topological diversity of these recently devised artificial beta-barrels with regard to their length. For this purpose, homologous p-octiphenyl, p-sexiphenyl, and p-quarterphenyl rods were equipped with complementary tripeptide strands based on the sequences Lys-Leu-Lys and Glu-Leu-Glu. The stability of rigid-rod beta-barrels of different length was determined by denaturation with guanidinium chloride. Free energies of delta GH2O = -5.2 kcalmol-1, delta GH2O = -2.9 kcalmol-1, and delta GH2O < -0.3 kcalmol-1 found for homologous p-octiphenyl, p-sexiphenyl, and p-quarterphenyl beta-barrels demonstrated strong dependence of beta-barrel stability on beta-barrel length. These results revealed a very qualitative minimal (approximately 23 A) and an "ideal" beta-barrel length (approximately 34 A), synergistic formation (alpha = 1.4) and remarkable stability for "ideal" p-octiphenyl beta-barrels exceeding that of several proteins and most synthetic models. Rigid-rod beta-barrels with p-oligophenyl "staves" longer than approximately 34 A will be very difficult to make and study because of rapidly decreasing rod solubilities. However, a strategy to bypass this apparent upper limitation of beta-barrel length is introduced: supramolecular matching of mismatched rods yielded elongated beta-barrels (61 A) of acceptable stability (delta GH2O = 2.2 - 3.1 kcalmol-1).     

Stability and morphology comparisons of self-assembled virus-like particles from wild-type and mutant human hepatitis B virus capsid proteins

Instead of displaying the wild-type selective export of virions containing mature genomes, human hepatitis B virus (HBV) mutant I97L, changing from an isoleucine to a leucine at amino acid 97 of HBV core antigen (HBcAg), lost the high stringency of selectivity in genome maturity during virion export. To understand the structural basis of this so-called "immature secretion" phenomenon, we compared the stability and morphology of self-assembled capsid particles from the wild-type and mutant I97L HBV, in either full-length (HBcAg1-183) or truncated core protein contexts (HBcAg1-149 and HBcAg1-140). Using negative staining and electron microscopy, full-length particles appear as "thick-walled" spherical particles with little interior space, whereas truncated particles appear as "thin-walled" spherical particles with a much larger inner space. We found no significant differences in capsid stability between wild-type and mutant I97L particles under denaturing pH and temperature in either full-length or truncated core protein contexts. In general, HBV capsid particles (HBcAg1-183, HBcAg1-149, and HBcAg1-140) are very robust but will dissociate at pH 2 or 14, at temperatures higher than 75 degrees C, or in 0.1% sodium dodecyl sulfate (SDS). An unexpected upshift banding pattern of the SDS-treated full-length particles during agarose gel electrophoresis is most likely caused by disulfide bonding of the last cysteine of HBcAg. HBV capsids are known to exist in natural infection as dimorphic T=3 or T=4 icosahedral particles. No difference in the ratio between T=3 (78%) and T=4 particles (20.3%) are found between wild-type HBV and mutant I97L in the context of HBcAg1-140. In addition, we found no difference in capsid stability between T=3 and T=4 particles successfully separated by using a novel agarose gel electrophoresis procedure.