Asymmetric distribution

Dehner Neuroblast divisions are asymmetric not just because the cell determinants are distributed asymmetrically, but also the size of the GMC is very different, as is the nuclear size. Is nuclear size difference present from the outset If you look at cells in telophase, are the nuclei the same size ... 

In the plasma membrane of animals (1), the amount of cholesterol is usually around 20-30 mol%. The rest of the lipids are mainly PC, PE, and sphingomyelin (SM) lipids, with smaller amounts of PS, PI, and glycolipids. These lipids are distributed asymmetrically across the membrane, because most cholesterol, PC, and glycolipids are located in the extracellular (outer) leaflet, whereas PS and PE lipids are located mainly in the intracellular (inner) monolayer. The lipid composition can be highly different in other organelles, however, as is the case in mitochondria (1), in which the mitochondrial membrane is composed of two (inner and outer) membranes. There, the amounts of cholesterol, SM, and PS are negligible most lipids are PC and PE. The major difference compared with plasma membrane is the concentration of cardiolipins. They are actually found only in bacterial and in mitochondrial membranes, where their numbers are significant even in mitochondria they are located mainly on the iimer membrane. 

Asymmetry in the lipid distribution over the bilayer could also be controlled in a similar way by the lateral packing pressure, which is likely to differ between constituent monolayers, due to the distinct chemical environments inside and outside the membrane. The enzymes involved may also be distributed asymmetrically. A configuration with constant, but nonzero, mean curvature, shown in Fig. 5.7, reflects such a situation. A membrane-spatming protein can then be viewed as a sensor of the lateral packing pressure in both monolayers. This speculation has some experimental justification. In a recent study of chromaffin granules, trans-membrane lipid asymmetry was shown to be induced by an ATP-dependent "flippase" [35]. 

Glycoproteins play major roles in antigen-antibody reactions, hormone function, enzyme catalysis, and cell-cell interactions. Membrane glycoproteins have domains of hydrophilic and hydrophobic sequences and are amphi-pathic molecules. The carbohydrate moieties of glycoproteins are distributed asymmetrically in cell membranes, cluster near one end of the protein molecule (Figure 10-7), and constitute a hydrophilic domain of amino acid residues (Chapter 21) as well as carbohydrates. The hydrophobic domain of the molecule interacts with the lipid bilayer. 

The galactolipids are known to be distributed asymmetrically in the lipid bilayer - about 60% of the galactoUpids are present in the outer leaflets and 40% in the inner leaflets of the thylakoid-membrane bilayer. The strong interaction between the head-groups of the galactolipid molecules determine then-packing properties and enhance the stability of the membrane. Formation of the bilayer structure of the thylakoid membrane also depends on the presence of proteins. Another characteristic of the thylakoid lipids is their high content ofthe trienoic acid, (C18 3) a-linolenic acid, which contributes to the fluidity of the membrane, necessary for the diffusion of lipophilic compounds such as plastoquinone, and the lateral diffusion of protein complexes. 

Viral NA is an exoglycosidase that hydrolyses terminal sialic acid residues from any glycoconjugate, including the viral glycoproteins themselves. The virion NA spikes are tetramers of the NA molecules that are anchored in the lipid bilayer by an amino-terminal hydrophobic amino acid sequence. Unlike HA, NA does not undergo post-translational proteolytic processing, and the NA spikes are distributed asymmetrically on the surfaces of the progeny virions. 

In many, possibly all, biological membranes, the lipids are distributed asymmetrically. The outer half of the bilayer consists mainly of neutral lipids, whereas the inner half contains the negatively charged examples, particularly phosphatidylserine. The interior of such a membrane can be 300 mV more positive than the solution that bathes the outside. Such differences in potential can be measured by the potassium nonactin probe (Latorreand Hall, 1976) (see Section 14.2 for nonactin). Such potential differences indicate the source of some typical membrane properties such as the gating potentials of nerves. 

If it concerns a rotation in the case of the movement of the body, then its inhomogeneity leads to a so-called imbalance. Depending on the number of revolutions n = tS/2ir and the mass distribution asymmetrical to the rotation axis... 

Due to the constant motion of the electrons, an atom or molecule develops a temporary (instantaneous) dipole when its electrons are distributed asymmetrically about the nucleus. A second atom or molecule, in turn, is distorted by the appearance of the dipole in the first atom or molecule (because electrons repel one another) which leads to an electrostatic attraction between the two atoms or molecules (Figure 4.42). Dispersion forces are present between two molecules (even non-polar molecules) when they are in close proximity. As an adsorbate, the molecules can be closer to each other than in the liquid state they are certainly close to the carbon atoms of the walls of the porosity. 

It is now well established that the protein complexes which are involved in photosynthetic electron, proton transport and phosphorylation activities are distributed asymmetrically, both in the plane of and across the thylakoid membrane. Such an asymmetric arrangement of proteins supports the vectorial properties of the membrane which are necessary for energy conservation. During these past few years, considerable efforts have been made to determine whether a similar heterogeneity existed for acyl lipids which are the second major components of this membrane [1,2]. 

The stereospecific distribution of fatty acids in the native borage and evening primrose oils have previously been reported 18). In native borage oil, GLA was distributed asymmetrically and preferentially located at the sn 2 and snA positions 18). In native evening primrose oil, GLA was concentrated in the snA position 18). Linoleic acid (LA 18 2n-6) was fairly evenly distributed in all positions of native evening primrose oil, but was preferentially located in the snA position of native borage oil 18). The results of our study showed that in DHA-enriched borage oil, GLA was mainly located in the sn-2 (18.4%) and snA... 

Source directivity caused by particular rupture orientation can play a significant role in distributing asymmetrically the intensity effects at regional scale. 

For reasons of symmetry the X2 molecule already treated does not exhibit any permanent dipole moment. Permanent dipole moments are always the result of the charge being distributed asymmetrically in the bonded state, and thus occur in diatomic molecules formed from different atoms. According to... 

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