Membrane limited vesicle

FIGURE 3-23 Motor protein-dependent movement of cargo. The head domains of myosin, dynein, and kinesin motor proteins bind to a cytoskeletal fiber (microfilaments or microtubules), and the tail domain attaches to one of various types of cargo—in this case, a membrane-limited vesicle. Hydrolysis of ATP in the head domain causes the head domain to "walk" along the track in one direction by a repeating cycle of conformational changes. 

Three-dimensional reconstructions from serial sections of a Golgi complex reveal this organelle to be a series of flattened membrane vesicles or sacs (cisternae), surrounded by a number of more or less spherical membrane-limited vesicles (Figure 5-23). The stack of Golgi cisternae has three de-... 

Myosins I, V, and VI power Intracellular translocation of some membrane-limited vesicles along actin filaments. A similar process Is responsible for c rt oplasmIc streaming, which Is probably mediated by myosin XI, one of the fastest moving myosins (see Figure 19-19). 

Within cells, proteins, organelles, and other membrane-limited vesicles, organelles, and proteins are frequendy transported distances of many micrometers along well-defined routes In the cytosol and delivered to particular addresses. Diffusion alone cannot account for the rate, directionality, and destinations of such transport processes. Findings from early experiments with fish-scale pigment cells and nerve cells first demonstrated that microtubules function as tracks In the Intracellular transport of various types of cargo. Eventually, two families of motor proteins—kinesins and dyneins— were found to mediate transport along microtubules. 

Two families of motor proteins, kInesIn and dynein, transport membrane-limited vesicles, proteins, and organelles along microtubules (see Table 20-2). 

One of the most puzzling structures within C. parvum sporozoites, is the crystalloid body (CB), which is also in intimate contact with the relic mitochondrion, outer nuclear membrane, and RER (Fig. 1) (Keithly et al. 2005). Although it is still unclear whether this organelle is surrounded by a limiting membrane, or is simply a complex of closely packed membrane-bounded vesicles, it has been shown that like the relic mitochondrion, the CB takes up mitotracker dyes (Ctrnacta et al. 2006 Kayser et al. 2002 Keithly et al. 

The acrosome is a secretory granule that is assembled in spermatids by the coalescence of Golgi apparatus-derived vesicles. This process produces a large, membrane-limited organelle with an inner acrosomal membrane apposed to the nucleus, an outer acrosomal membrane subjacent to the plasmalemma, and an equatorial segment where these two membrane domains intersect. Our inability to obtain highly purified preparations of isolated acrosomes, despite earlier claims to the contrary (Hartree, 1977), has limited our understanding of the function of this or-... 

The eukaryotic cell is demarcated from the external environment by the plasma membrane and organized into membrane-limited internal compartments (organelles and vesicles). 

Several minutes after proteins are synthesized In the rough ER, most of them leave the organelle within small membrane-bounded transport vesicles. These vesicles, which bud from regions of the rough ER not coated with ribosomes, carry the proteins to another membrane-limited organelle, the Golgi complex (see Figure 5-22). 

These observations were among the first to suggest that microtubules play a role In the Intracellular transport of membrane-limited organelles and vesicles. Other examples of such transport and the motor proteins that power them are described In Section 20.2. 

As described earlier, most of the studies on photocontrolled transport phenomenon focused on azobenzene-doped organic platforms such as planar lipid membranes and spherical vesicles, which have an intrinsic disadvantage. Those lipid membranes and vesicles are delicate and unstable, thus limiting their practical applications. Incorporation of the azobenzene moieties into a robust inorganic matrix greatly enhances the system stability and facilitates the device fabrication. For example, azobenzene moieties precisely positioned onto the pore surfaces of mesoporous silica membranes enable novel photocontrolled transport in the resulting composite materials (Liu et al., 2004). 

The localization of ArOH in lipid membrane of vesicles was proved by fluorescence quenching by hydrophylic ions. The ratio of observed Stern-Volmer quenching constant in vesicle solution to the same constant in aqueous solution gives evaluation of lower limit of the fraction of the investigated compound located in the aqueous phase [11]. This method can be applied most easy to the compounds which... 

Evidence indicating that, in interphase nuclei, the chromosomes are attached to the nuclear membrane comes from ultrastructural studies and from analysis of the segregation of newly synthesized DNA. Woollam et al. (1967) describe attachment of both distal and centro-meric ends of pachytene chromosomes to the nuclear membrane of mouse spermatocytes moreover, these authors suggest, on the basis of the nearness of centromeric attachments to the sex vesicle in these cells, that centromeric and distal attachment points are at opposite poles of the nucleus (cf. also, Sved, 1966). Davies and Tooze (1966) have examined mitotic chromosomes of newt erythroblasts, a cell type characterized by scarcity of endoplasmic reticulum. In interphase erythroblasts, numerous areas are found where chromatin appears to be closely associated with the nuclear membrane. At mitosis the chromosomes are observed to carry fragments of nuclear membrane, sometimes appearing as membrane-limited sheets of chromatin, continuous with the chromosomes. 

Neurotransmitter Transporters. Figure 3 Dopamine turnover at a presynaptic nerve terminal, (a) Dopamine is produced by tyrosine hydroxylase (TH). When secretory vesicles are filled, they join the releasable pool of vesicles at the presynaptic membrane. Upon exocytosis, the diffusion of released dopamine is limited by reuptake via DAT. (b) If DAT is inactive, dopamine spreads in the cerebrospinal fluid but cannot accumulate in secretory vesicles. This results in a compensatory increase of dopamine hydroxylase activity and a higher extracellular dopamine level mice with inactive DAT are hyperactive. 

Due to their physicochemical properties trace amines can pass the cell membrane to a limited extent by passive diffusion, with the more lipophilic PEA and TRP crossing membranes more readily than the more polar amines TYR. and OCT. In spite of these features, trace amines show a heterogeneous tissue distribution in the vertebrate brain, and for TYR. and OCT storage in synaptic vesicles as well as activity-dependent release have been demonstrated. So far, trace amines have always been found co-localized with monoamine neurotransmitters, and there is no evidence for neurons or synapses exclusively containing trace amines. 

Figure 20.1 Schematic diagram illustrating how antidepressants increase the concentration of extraneuronal neurotransmitter (noradrenaline and/or 5-HT). In the absence of drug (b), monoamine oxidase on the outer membrane of mitochondria metabolises cytoplasmic neurotransmitter and limits its concentration. Also, transmitter released by exocytosis is sequestered from the extracellular space by the membrane-bound transporters which limit the concentration of extraneuronal transmitter. In the presence of a MAO inhibitor (a), the concentration of cytoplasmic transmitter increases, causing a secondary increase in the vesicular pool of transmitter (illustrated by the increase in the size of the vesicle core). As a consequence, exocytotic release of transmitter is increased. Blocking the inhibitory presynaptic autoreceptors would also increase transmitter release, as shown by the absence of this receptor in the figure. In the presence of a neuronal reuptake inhibitor (c), the membrane-bound transporter is inactivated and the clearance of transmitter from the synapse is diminished...

Ehwald, R., Heese, P., and Klein, U., Determination of size limits of membrane separation in vesicle chromatography by fractionation of a polydisperse dex-tran, /. Chromatogr., 542, 239, 1991. 

The most important application recently developed for synthetic liposomes is as potential drug carriers for controlled release, especially for cancer chemotherapy (7). In general, the success of liposomes as vehicles for the transport of specific drugs will largely depend on their stability under physiological conditions. Unlike the naturally occurring membranes, the synthetic vesicles have very limited stability, and this is a... 

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