Cells topology

The matrices B(k) = Bji(k) include all relevant information concerning the intra-cell topology and the way in which the ceUs of the network are connected to each other. All in all there are k-values and therefore different B(k) matrices. Using the B(k) matrices, the Langevin equations, Eq. 2, are reduced to [31,73,74] ... 

That of the crystallographic axes, which is related to the seven crystal systems. That of unit-cell topology, which is related to the fourteen Bravais lattices or... 

Figure 6 Topology of helical transmembrane proteins. In one class of membrane proteins, typically apolar helical segments are embedded in the lipid bilayer oriented perpendicular to the surface of the membrane. The helices can be regarded as more or less rigid cylinders. The orientation of the helical axes, i.e., the topology of the transmembiane protein, can be defined by the orientation of the first N-terminal residues with respect to the cell. Topology is defined as out when the protein N-term (first residue) starts on the extra-cytoplasmic region (protein A), and as in if the N-term starts on the intra-cytoplasmic side (proteins B and C)...

The native form of chromatin in cells assumes a higher order stmcture called the 30-nm filament, which adopts a solenoidal stmcture where the 10-nm filament is arranged in a left-handed cod (Fig. 5). The negative supercoiling of the DNA is manifested by writhing the hehcal axis around the nucleosomes. Chromatin stmcture is an example of toroidal winding whereas eukaryotic chromosomes are linear, the chromatin stmctures, attached to a nuclear matrix, define separate closed-circular topological domains. 

Figure 46-8. Fusion of a vesicle with the plasma membrane preserves the orientation of any integral proteins embedded in the vesicle bilayer. Initially, the amino terminal of the protein faces the lumen, or inner cavity, of such a vesicle. After fusion, the amino terminal is on the exterior surface of the plasma membrane. That the orientation of the protein has not been reversed can be perceived by noting that the other end of the molecule, the carboxyl terminal, is always immersed in the cytoplasm. The lumen of a vesicle and the outside of the cell are topologically equivalent. (Re drawn and modified, with permission, from Lodish HF, Rothman JE The assembly of cell membranes. Sci Am [Jan] 1979 240 43.)...

Abremski, K., Hoess, R., and Sternberg, N. (1983). Studies on the properties of PI site-specific recombination evidence for topologically unlinked products following recombination. Cell 32, 1301-1311. 

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