Intercellular cytoplasmic processes

The problem of regenerating AI ) from NADH for cytoplasmic processes by using mitochondria is solved in the most energy-efficient manner by which one of the following intercellular shuttle systems ... 

In addition to the epithelial cells, the dendritic cells, which reside at the base of the epithelium and reach up to the tight junctions, with numerous intercellular (dendritic) cytoplasmic processes, constitute a principal cell population in the airways. The dendritic cells are extensively described in Chapter 11. 

The pathway of the metabolic process converting the original nutrients, which are of rather complex composition, to the simple end products of COj and HjO is long and complicated and consists of a large number of intermediate steps. Many of them are associated with electron and proton (or hydrogen-atom) transfer from the reduced species of one redox system to the oxidized species of another redox system. These steps as a rule occur, not homogeneously (in the cytoplasm or intercellular solution) but at the surfaces of special protein molecules, the enzymes, which are built into the intracellular membranes. Enzymes function as specific catalysts for given steps. 

Models of lipid bilayers have been employed widely to investigate diffusion properties across membranes through assisted and non-assisted mechanisms. Simple monovalent ions, e.g., Na+, K+, and Cl, have been shown to play a crucial role in intercellular communication. In order to enter the cell, the ion must preliminarily permeate the membrane that acts as an impervious wall towards the cytoplasm. Passive transport of Na+ and Cl ions across membranes has been investigated using a model lipid bilayer that undergoes severe deformations upon translocation of the ions across the aqueous interface [126]. This process is accompanied by thinning defects in the membrane and the formation of water fingers that ensure appropriate hydration of the ion as it permeates the hydrophobic environment. 

Fig. 1. Proposed process by which an infection thread passes through a cell wall between two plant cells, in this case between the root hair cell and an adjacent cortical cell. (1) The membrane at the tip of the infection thread has fused with the root hair cell plasma membrane to form a pore. Tonoplast membrane, TM infection thread membrane ITM rhizobia, R infection thread wall, ITW root hair cell cytoplasm, RHCC root hair cell plasma membrane, RHCP plant cell wall, PCW cortex cell plasma membrane, CCP cortex cell cytoplasm, CCC. The arrows and vesicles represent intense activity of the endomembrane system involved in the synthesis of membranes and wall material. (2) The rhizobia have forced their way, by dividing, into the region between the two cells although they are still enclosed by wall material. (3) An intercellular infection thread is formed by degradation and resyntheses of cell wall material in the vicinity of the dividing rhizobia. (4) The infection thread has entered the cortical cell by promoting invagination and growth of the plasma membrane and wall of that cell, in front of the dividing bacteria.

The C4 pathway in the plants of group (i) (NADP-malic enzyme eq. 1) is shown in the Fig. Air passes through the open stomata of the leaf into the extensive intercellular spaces and bathes the mesophyll cells. COj passes into the cytoplasm of these cells where it dissolves and ionizes the latter process is probably facilitated by carbonic anhydrase (EC... 

Finally, certain membrane proteins act as cellular specific receptors. They permit the yeast to react to various external stimuli such as sexual hormones or changes in the concentration of external nutrients. The activation of these membrane proteins triggers the liberation of compounds such as cyclic adenosine monophosphate (cAMP) in the cytoplasm. These compounds serve as secondary messengers which set off other intercellular reactions. The consequences of these cellular mechanisms in the alcoholic fermentation process merit further study. 

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