Membrane structure/function relations

The structure-function relations of glycolipids in lipid membranes has been reviewed. This is a challenging endeavour which has mainly been faced through NMR spectroscopy and computational modelling, using model membranes such as micelles, bicelles, and bilayers. Glycolipid structure is rarely, if ever, a unique low-energy conformer, but an ensemble of dynamic states. ... 

Packer, L. Membrane structure in relation to function of energy-transducing organelles. Ann. N.Y. Acad. Sci. 227, 166-174(1974)... 

The structural hypothesis, which was formulated in response to observations that axonal transport rate components move as discrete waves, each with a characteristic rate and a distinctive composition, can explain the coherent transport of functionally related proteins and is consistent with the relatively small numbers of motor molecules in neurons. The only assumption is that the number of elements that can interact with transport motor complexes is limited, and this requires appropriate packaging of the transported material. Different rate components result from packaging of transported material into different, cytologically identifiable, structures. In fact, the faster rates reflect the transport of proteins preassembled as membranous organelles, including vesicles and... 

The mechanism of DEA toxicity is unknown but may be related to its high tissue accumulation and effects on phospholipid metabolism, resulting in alterations in membrane structure and function. ... 

The following experimental observations are related to biological membrane structure and function. Discuss the implications of each observation with respect to membrane structure. 

PB, the value of P will depend on the precise geometrical arrangement of the component phases. The problem is not analytically tractable, however, except in simple or idealised cases. Consequently, a large number of formulae of varying degrees of approximation and different physical connotations have been developed in various fields. The relations best known in the diffusion field appear in reviews by Barrer 88) and Crank 89) but appreciation of their relative merits and physical significance is as yet very limited. Ideally, one would like to know which formula is appropriate for what type of composite membrane structure or, inversely, to deduce structural information about the membrane from measurements of P as a function of vA. 

Biochemical reactions are organized so that different reactions occur in different parts of the cell. This organization is most apparent in eukaryotes, where membrane-bounded structures are visible proof for the localization of different biochemical processes. For example, the synthesis of DNA and RNA takes place in the nucleus of a eukaryotic cell. The RNA is subsequently transported across the nuclear membrane to the cytoplasm, where it takes part in protein synthesis. Proteins made in the cytoplasm are used in all parts of the cell. A limited amount of protein synthesis also occurs in chloroplasts and mitochondria. Proteins made in these organelles are used exclusively in organelle-related functions. Most ATP synthesis occurs in chloroplasts and mitochondria. A host of reactions that transport nutrients and metabolites occur in the plasma membrane and the membranes of various organelles. The localization of functionally related reactions in different parts of the cell concentrates reactants and products at sites where they can be most efficiently utilized. 

B. Chance and D. Parsons, Cytochrome function in relation to inner membrane structure of mitochondria. Science 142 1176, 1963, 1963 by the AAAS.)... 

The structural organization of CNTs is functionally related to the fact that they intoxicate neurons via a four-step mechanism consisting of (1) binding, (2) internalization, (3) membrane translocation, and (4) enzymatic target modification (Figure 4) (Montecucco et al. 1994 Montecucco and Schiavo 1995 Rossetto et al. 2006). The LC is responsible for the intracellular catalytic activity, the amino-terminal 50kDa domain of the H chain (Hn) is implicated in membrane translocation, and the carboxy-terminal part (He) is mainly responsible for the neurospecific binding. 

The discussion of synthetic membranes can be structured in terms of the function or the structure of the membrane used in a particular application. For instance, one can consider whether a membrane is used to separate mixtures of gas molecules vs particles from liquids (function) vs whether the membrane structure is primarily microporous or dense (structure). In fact, function and stmcture are linked, but to facilitate the consideration of physical science issues related to membranes appropriate for this reference, emphasis on functional aspects are probably most appropriate. This approach reflects the fact that the use of a membrane generally involves one or more physical sci-... 

Our aim in this article is to provide the reader with some flavor of the various structures and functions related to lipids. Rather than presenting an exhaustive description of the topic, however, we prefer a down-to-earth approach on a level in which we combine many relevant views and methods with several instructive examples and highlights of recent studies. The concise list of references at the end of this article follows this idea, in accord with the style of this review series. The emphasis will be on lipid membranes because of their abundance in numerous biological systems, which include cellular membranes, liposomes, and other delivery vehicles. 

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