Danielli and Davson

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. 

Protein first came into the model as a result of considerations of interfacial tension. Danielli and Davson (1934/5) pointed out that measured interfacial tension at lipid-water interfaces was much higher than that evident at cell surfaces. Therefore they put forward a new model in which the lipid bilayer was encased in a sandwich of protein, thereby avoiding this problem and accommodating the protein known to be present in membranes. Thirty years later, the basic premise upon which protein was added to the model was shown to be incorrect (Haydon and Taylor, 1963) phospholipids have interfacial... 

Measurements of the intertecial tension of different living cells yielded very low values (0.1 to 0.2 dynes/cm in sea-urchin eggs), than that observed at lipid-water interfaces (10 to 15 dynes/cm). This observation led Danielli and Davson to propose a model comprising of a lipid bilayer with... 

Figure 1 The Danielli and Davson model for cell membrane Until the late 1960 s bilayer models were often perceived to be static structures but studies with a series of biophysical techniques involving X-ray diffraction, nuclear magnetic resonance (NMR) and electron spin resonance (ESR) spectroscopy, fluorescence microscopy, electron microscopy and others have revealed the dynamic nature of the cell membranes which have been summarized in the Singer and Nicolson s fluid mosaic model proposed in 1972 (see Figure 2).

D an ielli-D avson model of mem-Globular proteins (circular) cover phospholipid layers (club-shaped figures) which are separated by neutral lipoid region. Taken, with kind permission, from Danielli and Davson (1935), p.498. 

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... 

Pankhurst A.C. Riddiford, eds), Pergamon Press, New York, pp. 246-265 Danielli, J.F., and Davson, H. (1934/5) The Permeability of Thin Films , Journal of Cellular and Comparative Physiology, 5, 495-508... 

Danielli, J. F., and Davson, H., 1935, A contribution to the theory of permeability of thin films, J. Cell. Comp. Physiol. 5 495. 

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. 

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-... 

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... 

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... 

A. The Davson-Danielli-Robertson Model. This was the most widely accepted model in 1971, when Singer s review was published. In this model, the phospholipids are arranged as a bilayer. Proteins are found on both surfaces of the bilayer, attached to it by ionic interactions between the charged head groups of the phospholipids and charged groups in the proteins. Crucially, there is no protein in the interior of the bilayer. 

Davson, H., and Danielli, J.F. 1952. The Permeability of Natural Membranes, 2nd ed. Cambridge University Press, Cambridge, UK. 

H. Davson and J.F. Danielli, Permeability of Natural Membranes (Cambridge University Press, London) 2nd Edn. (1952). 

Cell Membranes The sequence of models of membrane structure Danielli-Davson Robertson S inger-N icholson The fluid mosaic model of cell membrane structure The interplay between data and models in the development of models of cell structure... 

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