von Raycho Yonchev
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| [1.] Ry/Fragment 022 01 - Diskussion Zuletzt bearbeitet: 2016-01-20 11:39:36 Klgn | Anézo 2003, Fragment, Gesichtet, KomplettPlagiat, Ry, SMWFragment, Schutzlevel sysop |
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| Untersuchte Arbeit: Seite: 22, Zeilen: 1 ff. (entire page) |
Quelle: Anézo 2003 Seite(n): 35 f., Zeilen: 35: 16 ff.; 36: 1 ff. |
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| [The effects of cholesterol on the phospholipid phase behavior are however much more complex than described above and are strongly] dependent on the cholesterol concentration. Cholesterol can induce domain formation in membranes in the liquid crystalline state and tends to promote the transition towards inverse phases such as HII [17].
Effect of the solutes. The incorporation of solutes into a phospholipid assembly can modify the phase equilibrium in a great number of ways. Polar solutes generally cause an osmotic dehydration of phospholipid systems, since they are in competition with the phospholipid headgroups to interact with water [18]. The dehydration effect is enhanced if the solute directly binds to the phospholipid headgroup, replacing bound water molecules. The introduction of polar solutes tends to favor the formation of ordered phases and inverse non-lamellar phases. Amphiphilic solutes preferentially adsorb with their polar moiety near the phospholipid headgroups and their hydrophobic part embedded within the phospholipid hydrocarbon region. Their effects are closely related to their chemical structure and cannot be generalized. Non-polar solutes tend to reduce chain packing constraints by partitioning into the interstices within the hydrocarbon regions of the phospholipid phase. They facilitate thereby the formation of inverse phases such as HII, where there is a significant degree of chain stress due to the necessity to fill the hydrophobic region at a uniform density [11]. I.2.4 Motional properties and membrane fluidity The dynamic properties of a phospholipid membrane in the biologically relevant liquid crystalline state arise from the conformational flexibility of its components. Conformational flexibility implying motion, the determination of the rate and extent of phospholipid motions is essential for understanding dynamic properties of membranes. The major motivation for studying membrane dynamics is its relevance to biological functions. At first, it is important to make a distinction between motional order and motional rates. The two concepts are independent, even if changes in motional rates often parallel changes in motional order. Motional order on one hand, and motional rates on the other hand, provide different insights into the membrane dynamics, which can be [combined to obtain an overall vision of the complex dynamic properties.] 11. Seddon, J. M.; Templer, R. H. Handbook of Biological Physics - Structure and Dynamics of Membranes: From Cells to Vesicles; Elsevier Science: Amsterdam, 1995; Vol. 1A. 17. Ohvo-Rekila [sic], H.; Ramstedt, B.; Leppimaki [sic], P.; Slotte, J. P. Prog. Lipid Res. 2002, 41, 66. 18. Cevc, G. Biochemistry 1991, 30, 7186. |
The effects of cholesterol on the phospholipid phase behavior are however much more complex than described above and are strongly dependent on the cholesterol concentration.
Cholesterol can induce domain formation in membranes in the liquid crystalline state and tends to promote the transition towards inverse phases such as HII [26]. Effect of solutes The incorporation of solutes into a phospholipid assembly can modify the phase equilibria in a great number of ways. Polar solutes generally cause an osmotic dehydration of phospholipid systems, since they are in competition with the phospholipid headgroups to interact with water [27]. The dehydration effect is enhanced if the solute directly binds to the phospholipid headgroup, replacing bound water molecules. The introduction of polar solutes tends to favor the formation of ordered phases and inverse non-lamellar phases. Amphiphilic solutes preferentially adsorb with their polar moiety near the phospholipid headgroups and their hydrophobic part embedded within the phospholipid hydrocarbon region. Their effects are closely related to their chemical structure and cannot be generalized. Non-polar solutes tend to reduce chain packing constraints by partitioning into the interstices within the hydrocarbon regions of the phospholipid phase. They facilitate thereby the formation of inverse phases such as HII, where there is a significant degree of chain stress due to the necessity to fill the hydrophobic region at a uniform density [20]. [page 36:] 1.2.4 Motional properties and membrane fluidity The dynamic properties of a phospholipid membrane in the biologically relevant liquid crystalline state arise from the conformational flexibility of its components. Conformational flexibility implying motion, the determination of the rate and extent of phospholipid motions is essential for understanding dynamic properties of membranes. The major motivation for studying membrane dynamics is its relevance to biological functions. At first, it is important to make a distinction between motional order and motional rates. The two concepts are independent, even if changes in motional rates often parallel changes in motional order. Motional order on one hand, and motional rates on the other hand, provide different insights into the membrane dynamics which can be combined to obtain an overall vision of the complex dynamic properties. [20] J. M. Seddon and R. H. Templer. Polymorphism of Lipid-Water Systems. In: Handbook of Biological Physics - Structure and Dynamics of Membranes: From Cells to Vesicles, volume 1A. Elsevier Science, R. Lipowsky and E. Sackmann (Eds.), Amsterdam, 1995. [26] H. Ohvo-Rekilä, B. Ramstedt, P. Leppimäki, and J. P. Slotte. Prog. Lipid Res., 41:66–97, 2002. [27] G. Cevc. Biochemistry, 30:7186–7193, 1991. |
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