Envelope membrane inner layer

Cell envelopes of prokaryotic organisms (archaea and bacteria) are characterized by the presence of two distinct components the cytoplasmic membrane, which constitutes the inner layer, and an outer supramolecular layered cell wall (for reviews see Ref. 4), which pre-... 

III. The inner envelope a syncytial layer showing much variation. Some workers divide this layer into two zones - zone I, a cytoplasmic layer and zone II, a gelatinous layer (Fig. 7.14). Part of this embryonic layer gives rise to the embryophore (Fig. 7.4) and also to the oncospheral membrane (Figs. 7.4, 7.11 and 7.14) (a very thin layer surrounding the oncosphere), which is often counted as a fourth layer. Additional layers, which may be further derived from the above basic envelopes have been reported in some species (e.g. H. nana 204), but it is beyond the scope of this text to discuss all the various modifications which can occur. Only those features which have a special physiological significance are discussed below. 

The structure, ultrastructure and formation of the hymenolepidid egg has been reviewed in detail by Ubelaker (888). Its general morphology is shown in Fig. 7.14). Although there are only the usual three basic embryonic membranes (p. 179) in the developing egg - shell/capsule, outer envelope, and inner envelope - the fully formed egg often appears to be more complex due to further differentiation of these layers. The following structures can be recognised (Fig. 7.11). 

The cytoplasm of bacteria is surrounded by a cell envelope which is composed of several layers. The inner layer, the cytoplasmic membrane, is in direct contact with the cytoplasm. It consists of a liquid-crystalline bilayer of phospholipids in which proteins are embedded. 

Flg. 13. The chloroplast envelope plays a predominant role in the assembly of the three parts of the galactolipid molecule (galactose, glycerol, fatty acids). Saturated and monounsat-urated fatty acids are synthesized in the stroma by a multienzyme complex (fatty acid synthetase). Then, the different steps occur on the envelope, probably at the level of the inner membrane. Under these conditions, massive transport of galactolipids should occur very rapidly between the inner layer of the inner envelope membrane and the thylakoids (reproduced from Douce and Joyaid, 1979a, by permission). 

The cyanobacteria (blue-green algae) are classified as Gram-negative bacteria (Stanier et al., 1976). Their cell envelope is composed of the outer membrane and plasma (or cytoplasmic) membrane separated by a peptido-glycan layer. In addition, they have intracellular photosynthetic membranes, i.e., the thylakoid membranes. Their membrane structure is similar to that of eukaryotic plant chloroplast, which contains outer and inner envelope membranes, surrounding the thylakoid membranes. 

Alphaviruses, such as Sindbis virus and Semliki Forest virus, are a group of mosquito-borne, enveloped RNA viruses that can cause encephalitis, fever, arthritis and rashes in mammals. These viruses have two protein shells—an outer glycoprotein layer and an inner core— which are separated by a lipid bilayer, a membrane. Studies by cryoelectron microscopy have shown that... 

In Gram-negative bacteria which are characterised by a rather complex cell envelope, the CM is also referred to as inner membrane to distinguish it from a second lipid bilayer, termed outer membrane (OM). The space between these two layers is called the periplasm (PP). In the periplasmic space, many proteins are found with a variety of functions. Some are involved in biosynthesis and/or export of cell wall components and surface structures (e.g. pili, flagellae,... 

The nucleus is separated from the cytoplasm by the nuclear envelope, which consists of the outer and inner nuclear membranes. Each of the two nuclear membranes has two layers, and the membranes are separated from each other by the perinuclear space. The outer nuclear membrane is continuous with the rough endoplasmic reticulum and is covered with ribosomes. The inner side of the membrane is covered with a protein layer (the nuclear lamina), in which the nuclear structures are anchored. 

This envelope is a syncytial layer involving two cells Ailing the space between the embryo and the egg shell it is responsible for the formation of the embryophore and oncospheral membrane (204). After the latter is formed, what is left of the inner envelope becomes the cytoplasmic and gelatinous layers-zones I and II, respectively, in H. diminuta (Fig. 7.14). The latter has the ability to swell readily in dilute salt solutions, a property which may facilitate the escape of the oncosphere during hatching (p. 191) (442). 

This structure (Fig. 7.14) has received much attention due to the role it plays in the hatching process (see below). It is not a typical unit membrane but resembles a membranous lamina and consists of a layer of regularly arranged granules bounded on both sides by a number of lamina (442). Its chemical composition has not been determined but, in taeniid cestodes, there is some histochemical evidence that it may be a lipoprotein (442). It is apparently formed by the delamination of the inner part of the inner envelope, detaching from it as a thin, separate layer. 

Several investigators, using a variety of techniques and samples, have identified an electron-dense layer of material interposed between the inner nuclear membrane and the peripheral chromatin (Fig. 1). This layer has been termed the nuclear lamina (Fawcett, 1966). The nuclear lamina, together with inner and outer nuclear membranes and pore complexes, constitute the basic elements of the nuclear envelope. These structures have been observed in all eukaryotic cells (Franke, 1970, 1974). 

The complex three-layer membrane of Bangkok Airport s membrane roof is illustrated in Fig. 12.9. Here and as explained before, the high and lasting solar reflection of 70% of the outer waterproof PTFE/glass layer is also an important feature. To improve the acoustic properties of the roof, an additional middle layer has been included which consists of a cable net covered with transparent polycarbonate (PC) sheets. This, in conjunction with the translucent inner membrane liner, acts as a baffle. Figure 12.10 provides an interior view of the concourses with the innovative membrane envelope. 

Nanoparticles are classified into two groups according to preparation techniques, which are nanocapsules and nanospheres (see Figure 11.3). Nanocapsules are vesicular systems enveloped with a polymeric membrane film. The active substances are encapsulated in the inner core. Nanocapsules consist of oily core and unilayer polymeric membrane or aqueous core and double layer polymeric membrane, called nanocapsule and polymersome, respectively. Nanospheres are matrix-type colloidal particles and they do not have an oily core, in contrast to nanocapsules. Nanoparticles can be prepared directly from cationic polymers such as chitosan, PEI or PLL. These cationic nanoparticles have been studied extensively for nucleic acid delivery in particular. 

On electron micrographs prepared from tissues fixed in osmic acid, the nuclear membrane appears as an envelope 250 A thick composed of three different layers an inner and an outer dense lining (each measuring 60 A in thickness) and a less dense median space (120 A thick). Unlike the cell or the mitochondrial membranes, the nuclear envelope (see Fig. 2-2) is not continuous, but is frequently interrupted by circular pores 1000 A in diameter [1-9]. 

Fig. 5. Diagram showing the various cleavage planes of the bacterial envelope. OM Outer membrane, cleaving in plane I. IM Inner membrane, cleaving in plane II. The filled circles in OM represent proteins of the rigid layer. The open circles in IM represent particles typical of plane II.

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