Membranes Danielli

The most important addition to it was the proposal of protein-lined channels across the membrane (Danielli, 1958), which would allow for the selective passage of ions. This was the first suggestion that protein might actually cross the bilayer. 

Our knowledge of biological membrane ultrastructure has increased considerably over the years as a result of rapid advances in instrumentation. Although there is still controversy over the most correct biological membrane model, the concept of membrane structure presented by Davson and Danielli of a lipid bilayer is perhaps the one best accepted [12,13]. The most current version of that basic model, illustrated in Fig. 7, is referred to as the fluid mosaic model of membrane structure. This model is consistent with what we have learned about the existence of specific ion channels and receptors within and along surface membranes. 

H Davson, JF Danielli. The Permeability of Natural Membranes. 2nd ed. New York Cambridge University Press, 1952. 

Figure 7.2 Danielli-Davson membrane model. A layer of protein was thought to sandwich a lipid bilayer.

The first membrane model to be widely accepted was that proposed by Danielli and Davson in 1935 [528]. On the basis of the observation that proteins could be adsorbed to oil droplets obtained from mackerel eggs and other research, the two scientists at University College in London proposed the sandwich of lipids model (Fig. 7.2), where a bilayer is covered on both sides by a layer of protein. The model underwent revisions over the years, as more was learned from electron microscopic and X-ray diffraction studies. It was eventually replaced in the 1970s by the current model of the membrane, known as the fluid mosaic model, proposed by Singer and Nicolson [529,530]. In the new model (Fig. 7.3), the lipid bilayer was retained, but the proteins were proposed to be globular and to freely float within the lipid bilayer, some spanning the entire bilayer. 

M. M. Dubinin, Physical Adsorption of Gases and Vapors in Micropores, in Progress in Surface and Membrane Science, D. A. Cadenhead, J. F. Danielli, and M. D. Rosenberg, eds. [Academic Press, New York, 1975], pp. 1-70. 

At present there is considerable interest in the way in which the con-stituents of membranes are associated to form the dynamic complex entity of the cell membrane. Speculations range from the Danielli-type structure, first advanced in 1935, to structures which now place greater emphasis on the so-called hydrophobic bonding of the lipid polymethylene chains and amino acids of the membrane protein (10). Various other speculations about the associations of the membrane components are built around these two main themes. In a field of research where there are such a considerable speculation and divergence of opinion, this usually indicates a shortage of experimental information rather than variations in perspicacity. This seems to be true of our present knowledge of membrane structure. 

It is possible that quite different molecular architectures may occur in membranes from different sources. Current research may result in a much more dramatic revision or complete rejection of the bilayer model for some membranes, especially in such systems as mitochondria (30) and chloroplasts (2). However, it is also possible that structural differences are only variations on the basic theme of the bilayer, from myelin at one extreme to mitochondria or chloroplasts on the other. One must not readily reject the fundamentals of the Danielli concept, especially in view of the present inadequate knowledge of the properties of phospholipids in water. Clearly the molecular architecture of membranes is speculative, but most aspects of the problem are amenable to direct experimental test by the new physical techniques. A consistent model for biological membranes will emerge quickly. 

Another microscopic technique is to freeze the specimen and then fracture it with a knife. A knife cutting through the frozen specimen splits the membrane down the middle, exposing the inside of the bilayer (fig. 17.13a). If the Davson-Danielli model for membrane structure were correct, the two exposed surfaces would be featureless. However, electron micrographs of metallic casts of such samples reveal surfaces studded with particles of various sizes (fig. 17.13(f)- Additional studies indicate that these particles are proteins that are deeply embedded in the membrane. The particles seen on the inner and outer leaflets of the bilayer usually differ in size and distribution because of an asymmetrical disposition of the proteins across the bilayer. 

During the 1960s, various alternatives to the Davson-Danielli model were proposed. Some investigators abandoned the idea of a phospholipid bilayer and suggested instead that membranes consist of aggregates of lipid-protein complexes. However, in 1972, Jon Singer and Garth Nicol-... 

Why does the Davson-Danielli membrane model predict that the exposed inside of the lipid bilayer is featureless ... 

Although numerous models for the structure of membranes have been proposed, the structural features which are generally accepted at present are rather similar to the original Danielli-Davson model. There is convincing evidence that the structure is dominated by lipid bilayers. The state of order of the hydrocarbon chains is now being studied extensively by many groups (see below). Less is known about the proteins. Besides the proteins that are located on the outside according to the Danielli-Davson model, there are also proteins that are partly buried in the hydro-phobic interior of the lipid layer however, little is known about the lipid-protein interaction. 

Sodium and potassium ions are vital to the normal functioning of the nerve cell. The ions are separated by the cell membrane with sodium on the outside and potassium on the inside of the resting cell. A model of the basic membrane, which in principle was built as a bilayer according to the well known Davson-Danielli-Robertson scheme but which... 

J. F. Danielli (36) was the first to consider the membrane as a succession of potential barriers. Migration takes place in such a way that the elementary particles jump over the subsequent barriers. 

A F is the difference in free energy of the top and the foot of the barrier. The flux is determined by the difference in the free energies of activation for the different unit processes. B. J. Zwolinski, H. Eyeing and C. E. Reese (190) have extended the approach of Danielli. Their derivations are only valid in the case that the energy barriers are regularly divided, and if the distance between these barriers is very small. These authors consider also the effect of external forces. They obtain if there is an electrical potential gradient and a concentration gradient across the membrane , ... 

Danielli, J. F. in The permeability of natural membranes, by Davson and DanieLLI (Cambridge 1943), chap. XXI and appendix A. 

In 1943, Davson and Danielli introduced, in their seminal book The Permeability of Natural Membranes, the idea that solute permeability was not a generalized property of the plasma membrane but rather was associated with discrete and... 

The field has been fortunate in that in addition to the primary literature scattered in a wide range of biochemical journals there has been a bedrock of important monographs. In addition to Davson and Danielli (1943) Stein has written three monographs at approximately ten year intervals. The first, The Movement of Molecules across Cell Membranes, (1967) sought to be in the spirit of Davson and Danielli and indeed was published as one of a series of volumes of which Danielli was the editor. It expressed the hope that no more monographs of this type will... 

Davson, H. Danielli, J.F. (1943). Permeability of Natural Membranes. Cambridge University Press, Cambridge, UK. 

CADENHEAD, D.A. and DANIELLI, J.F. (editors), Progress in Surface and Membrane Science, Vols 1-, Academic Press (1964- )... 

Dubinin MM. Physical adsorption of gases and vapors in micropores. In Cadenhead DA, Danielli JF, Rosenberg MD, eds. Progress in Surface and Membranes Science, vol. 9, New York Academic Press. 1975 pp. 1-70. 

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