the Cage of a green plant. Membranes

you are: the Cage of a green plant

The Protolayer outside and from within is limited by membranes - plazmalemmoj and tonoplastom; plazmalemma separates it from a cellular wall, and tonoplast - from vakuoli. In an electronic microscope (at increase a million times and more) these membranes in appropriate way painted, look as two dark strips located on distance of 6-10 nanometers from each other. in a protolayer there are also various little bodies, so-called organelly. Among them first of all are evident one large kernel and numerous smaller mitohondrii and hloroplasty. Each of organell has functions. These functions are carried out in the unique internal environment created by selective permeability and other specific properties of membranes, surrounding organellu and separating it from all other protolayer. Selective permeability means that various substances get through the given membrane with different speeds, basically because of their different solubility in separate components of a membrane.

Are available also original ' pumps ', i.e. The systems which are actively pumping over through a membrane those or other substances with use for this purpose of energy. Non-uniform distribution of some substances or elements appears result of such activity: kaly, for example, is present usually at a protolayer in much higher concentration, rather than in the external environment whereas related to it an element sodium at the majority of plants practically ' is pushed out ' from a protolayer.

Differential tsentrifugirovanija membranes allocate with the Method from cages (thus in a deposit there is a mix of various membranes) and subject to the chemical analysis. In the course of membrane allocation are usually torn, as it is structures thin and fragile, with rather big area of a surface; however then the ends of their fragments often merge, and then there are spherical vials. The analysis of such vials received from a great number of various membranes, has revealed in them presence of two main components: the squirrel and fosfolipida. Lipidy from different membranes are adequately similar, as to fibers, to each type of membranes svojstven the type of fiber corresponding to those physiological functions which the given membrane carries out in a cage.

It is known, for example, that the active fibers (enzymes) regulating transport of mineral substances - their receipt in a cage and an exit from a cage, - are localised in plazmalemme and tonoplaste; the enzymes participating in photosynthesis, are concentrated in membrannyh systems green hloroplastov; and at last, enzymes, katalizirujushchie oxidising reactions of process of breath, are in mitohondrialnyh membranes.

If to mix corresponding fosfolipidy and fibers and to put this mix on a water surface are spontaneously formed membranopodobnye the structures similar on a thickness with biological membranes. Research of such artificial membranes prepared from fibers and lipidov of natural membranes, gives the chance to us to understand better structure and function of biological membranes. Artificial membranes find out different permeability for different ions depending on the nature of fibers and lipidov, entering into their structure. Extremely interesting effects can be observed at addition to artificial membranes of some antibiotics. Valinomitsin, for example, thanks to the structure (i.e.) it appears to the certain sizes and a molecule charge capable to draw and keep ions kalija, but does not draw sodium ions. If to add valinomitsin to the artificial membrane separating solutions with ions To + and Na + from at its finest speed of moving of ions To + through a membrane will increase several times whereas speed of carrying over of ions Na + remains almost invariable. Otherwise operates gramitsidin which molecule has other sizes and other structure: at addition to a membrane gramitsidina speed of carrying over of both ions - not only To +, but also Na + increases. Artificial membranes are used also for studying of mechanisms with which help light and hormones regulate growth of plants (about it we we will speak in gl. 11).

Plazmalemma is turned by one party to a cellular wall, and another - to cytoplasm; both these ovodnennye structures contact, as it is considered to be, with gidrofilnymi, the charged sites of membranes. As fibers contain more than the charged groups, than lipidy, in the first models of membranes it was supposed that plazmalemma consists of two external albuminous layers (two dark lines on fig. 2.3) and one lipidnogo a layer between them. Such model membrannoj structures remained conventional prior to the beginning of 1970th when some new data has been obtained and it became clear that the model requires revision. Incompatible with this model ' a sandwich ' there was, for example, the data of electronic microscopy received by a method of freezing - etchings. An investigated fabric at first freeze in liquid nitrogen, and then split a stupid microlanguid knife so skol passes in a plane parallel to a surface of a membrane (fig. 2.6). After that the sample maintain under vacuum for sublimation of ice (sublimation). This procedure also is called as etching. Then the sample napyljajut coal or metal to reveal details of a structure of the bared surface.

The remark (copy) of a surface of a preparation Received thus also is object of elektronno-microscopic research. On such remarks the membranes interspersed in a smooth surface large particles - globuljarnye fibers are visible. Special ' drawing ' the membrane surface managed presence to confirm and other method, namely by means of pectins - of special fibers (them allocate from seeds) which are attached to discrete and specific albuminous receptors on membrannoj surfaces and allow to reveal these receptors.

The Results received by these and some other methods, have given the chance to assume that membranes have a mosaic structure and consist from lipidnogo matriksa in which in different places fibers (fig. 2.8 are interspersed). Such model considers, what not all sites of an albuminous molecule gidrofilny, and lipidy not completely gidrofobny. According to this model, the charged (polar) groups albuminous and lipidnyh molecules are on an external surface of a membrane, in contact to cellular water, and not charged (not polar) groups form an internal waterproof part of a membrane. It is supposed also that one fibers are unsteadily attached to an external surface of a membrane whereas others (so-called integrated fibers) penetrate all thickness of a membrane. In such conclusion result biochemical experiments: they show that the part of fibers easily separates from membranes, and the branch of others appears possible only after full disintegration membrannoj structures.

On the basis of early studies the structure of membranes was represented to us stable and rigid, however recently the data, testifying that at least lipidnyj the component of membranes has the liquid nature quickly collects and, hence, is mobile. Besides, experiences with it is radioactive mechennymi predecessors separate membrannyh components have shown that speed of metabolic updating of some sites of a membrane is very high,

I.e. What is the sites continuously collapse and resintezirujutsja. Entering mechenye predecessors into a mature fabric, we can observe, how they join in membranes, remain in them throughout several hours, and then disappear from membranes and are found out in any other parts of a cage.