Intracellular phase

Example 11.1 Cell electric potentials In living systems, ions in the intracellular phase and the extracellular phase produce a potential difference of about 80 mV between the two phases. The intracellular phase potential is negative (Garby and Larsen, 1995). Determine the difference in electrical potential energy per mole positive monovalent ion, e.g., Na+, between the two phases. 

Three dominant processes in the reaction diffusion in biofilms and cellular systems are (1) diffusion in a continuous extracellular phase B, (2) transport of solutes across the membrane, and (3) diffusion and reaction in the intracellular phase A. Consider aerobic growth on a single carbon source. The volume-averaged equations of a substrate S and oxygen O (electron acceptor) transport are... 

The parameter / is the characteristic length for a unit cell, E0 is the surface concentration of a carrier protein molecule, and a2, a3, a4, a5 are the reaction rate parameters analogous to that half saturation constants. Table 11.3 displays the experimental effective diffusion coefficients and the volume fraction of intracellular phase A. In the first four sets... 

The stoichiometric coupling between the transport of an organic substrate (A) and a cation can be fairly easily represented by the carrier model of cotransport (Fig. 3). It is assumed that the transport is mediated by a membrane component (X) which can alternate between two states X and X", respectively. X is assumed to communicate with the -phase (e.g. extracellular phase) from which it can bind both ligands (A) and (B) to form the two binary complexes AX and BX and also a ternary complex ABX. On the other hand, the state X" communicates with the -phase (e.g. intracellular phase) from which it may bind A and/or B to form the complexes AX, BX" and ABX". The translocation of A and B between the two phases, and ", is assumed to be effected by the interconversion between the two states of each species of X, as has been described in more detail elsewhere (6,10,25,46,47). The transfer of energy between the transfers of A and B via cotransport requires that they move predominantly by ternary complex (ABX), and this implies either that the two binary complexes AX and BX are less ready to interconvert between the -state and "-state, respectively, than is the ternary complex, or that the two binary... 

Therefore, this implies that the proteins in the intracellular phase may have an important role in maintaining the production of action potential. Also, Tasaki has stressed the importance of the outer surface of the axon membrane in producing the membrane potential of an ion exchange membrane (Ca, K , or other monovalent cations. ). However, the explicit formulation for the membrane potential in terms of these views has not been put forward yet. 

For example, tetrodotoxin (TXX) and saxitoxin (STX) are inhibitors of the Na channel of squid axons when applied from the extracellular side. On the other hand, the specific inhibitors for K channels are tetraethyl-ammonium (TEA), Cs, etc. when applied from the intracellular phase. Also, Mn ", Co ", etc. are known to be Ca " channel inhibitors (Table 24). 

With the primmorph ceU culture system, the first solid evidence was provided that the synthesis of the spicules starts intracellularly (Muller et al., 2005). The process of spicule formation can be divided into an initial intracellular phase and a subsequent extracellular shaping phase. Silicic acid, the substrate for silicatein, is actively taken up by cells (sclerocytes) via the Na+ZHCOj" (Si(OH) ) cotransporter. In parallel, silicatein is synthesized, processed, and stored with silicic acid in special organelles of the sclerocytes, the silicasomes. Within these organelles, the axial filaments are formed, around which silica is deposited enzymatically. 

The majority of research-workers consider that a special structure surrounding the cell, called the cellular membrane , is the site of the various mechanisms which enable the cell to keep its content in the particular state observed. The opponents of this view assume that if such a thing as a membrane exists, it has no particular function the unequal distribution of ions and molecules depends on the very special properties exhibited by macromolecules in the intracellular phase. 

The thermodynamical activity of most of the ions or molecules constituting the intracellular phase is unknown, thus leaving much doubt as to the correctness of the generally accepted assumption that the activity coefiScient of many intracellular chemicals is very close to one. This last remark does not apply when dealing with exchanges between two extracellular components which are separated by a cellular layer. 

In the boundary between the extracellular and the intracellular phases, a more or less continuous drop in the concentration of the introduced labeled phosphate may take place. If a phosphorus compound is built up inside the phase boundary, it is very difficult to determine the specific... 

Volcani, 1974). The extracellular malaria parasites, Plasmodium bergheiy were shown to contain about half the amount of sialic acid per unit weight as the control red cell extract, although the sialic acid residues were not exposed to the outer surface of the cell membrane (Seed et al., 1974). Still to be investigated, as has been done with the Sindbis virus, is the extent of host dependency on the presence of sialic acids in this and other parasites which have extensive intracellular phases in their life cycles. 

Absorption intracellular phase. In the second phase of fat absorption, absorbed products are resynthesized in the enterocytes... 

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