Basic Structural Components Research Articles

The giant melanosome: A model of deranged melanosome-morphogenesis

A unique type of melanin granule, occurring in a nevoid pigmented lesion in man, is described. It grows to extraordinary size, it melanizes asynchronously and, in contrast to all other known melanosomes of mammals, it is essentially nonfilamentous in nature. Its basic structural components are 400 A microvesicles, which, during melanization, are gradually embedded in the melanin matrix. Evidence is presented that identical vesciles also occur in normal filamentous melanosomes of man. The giant melanosome is considered to result from a derangement of morphogenesis at a distinct stage of melanosome ontogeny.

GSL - a combined continuous and discrete simulation language

GSL is a FORTRAN-oriented language which combines the activity and process concepts of a discrete simula tion language with continuous simulation concepts, thereby permitting the simulation of systems which call for combining continuous and discrete simula tion techniques. The basic structural component of GSL is the simulation block, which corresponds either to an activity of a discrete system or a dynamic re gion of a continuous system. Both discrete and con tinuous simulation blocks may have multiple process instances which may be controlled dynamically at run- time. The result is a combined language which re tains the features of both continuous and discrete simulation languages and moreover takes advantage of the desirable features of each to supplement the other. GSL syntax is described by examples which illustrate the application of the language in a typical combined simulation problem and permit the evaluation of the various features of the language.

On the Size of the DNA in the Mammalian Chromosome: Structural Subunits

Alkaline degradation of mammalian DNA indicates that the molecule exists in the chromosome as an array of structural subunits. The size of the subunit of single-stranded DNA is circa 5 x 10(8) daltons, and it is of sufficient length to contain a number of synthetic units, replicons. The upper size limit of the multicomponent structure is in excess of 10(10) daltons. Mammalian cells of three different origins have been shown to contain the same basic structural DNA components and these components exist throughout the cell cycle. The nature of the links between the subunits is not known.

Formation of “Black” Lipid Membranes by Oxidation Products of Cholesterol

THE so-called bimolecular lipid leaflet1, postulated as a basic structural component of natural membranes, has only recently become available for direct experimental investigation2. The formation and properties of bilayer lipid and proteolipid membranes, separating two aqueous phases, have been investigated3–7. The thickness of these membranes in aqueous solution is of the order of 70 A, and they appear “black” when viewed by reflected light8. For this reason they are called “black” lipid membranes (or films) to distinguish them from the well known black soap films in air9.

Black lipid films in aqueous media: A new type of interfacial phenomenon: Experimental techniques and thickness measurements

The generally accepted model of the plasma membrane is that proposed by Danielli and Davson in which a bimolecular lipid film is pictured as the basic structural component separating two aqueous phases. Direct experimental studies of the postulated structure as ultrathin films have been reported recently. Since the thickness of these films is small in comparison with the wavelength of light, they appear to be black when viewed by reflected light owing to the phase reversal. Hence, these films in aqueous solutions are called “black lipid films” to distinguish them from the black soap films in air. Hitherto the black lipid films had been made only from either a complex lipid mixture or lecithins. The brush technique described by Mueller and co-workers had been used by subsequent investigators. However, this technique was found to be unsatisfactory, especially when the formation characteristics were to be studied and the compositions of lipid solution from which stable black films could be generated were to be established. This paper is concerned with experimental techniques for studying these ultra-thin lipid structures. The apparatus devised permits a rapid generation of fresh lipid-water interfaces under constant conditions; this should be generally useful for the investigation of this new type of interfacial adsorption phenomenon. In addition, the formation of black lipid films by compounds such as di- and triesters of polyhydric alcohols is reported. The thicker films first formed thinned gradually giving the usual sequence of interference colors. The thickness of these black films in different electrolyte solutions of varying concentration is found to be 50 ± 5 A. The 50 A thickness is deduced from quantitative measurements or reflected light intensities together with film refractive indices determined from measurements of Brewster's angle.

Structure and Photochemical Activity of Chlorophyll-Containing Particles from Rhodospirillum rubrum

Comparative studies on isolated chromatophores and on sectioned cells of the photosynthetic bacterium Rhodospirillum rubrum confirm the assumption expressed in earlier investigations that the photochemically active chromatophores isolated from disrupted cells represent structural chlorophyll-bearing components of the protoplast. Actively growing cells from light-grown cultures about 12 hours old do not release chromatophores when disrupted in dilute buffers, but do release smaller, chlorophyll-containing structures about 25 mmicro in diameter. Sections of such cells do not reveal chromatophores, but contain in the ground cytoplasm numerous particles somewhat smaller in size than the 25 mmicro chlorophyll-containing particles released from disrupted cells. Similar particles are obtained by the sonication of isolated chromatophores obtained from cells of 1-day-old cultures. The small, subchromatophore particles described here appear to be functionally complete units which are photochemically active in photo-oxidation, photoreduction, and photophosphorylation, and it is postulated that they represent the basic biochemical and structural components of the chromatophore.

Ultrastructure of retinal rod synapses of the guinea pig eye as revealed by three-dimensional reconstructions from serial sections

The structure of the synaptic bodies of the retinal receptors of the guinea pig eye and the synaptic connections of these receptors have been studied on three-dimensional reconstructions from serial sections. Series with up to forty ultrathin sections (average thickness 250 Å) were examined. Two types of synaptic bodies belonging to the α- and the β-cells respectively can be distinguished. Both types contain the same basic structural components: the synaptic granules or vesicles, the synaptic vacuoles and the synaptic ribbon. The α-cells are in synaptic contact with dendrites presumably belonging to two different bipolars. The dendrites end inside an invagination of the plasma membrane of the synaptic body at its vitreal pole and make contact with two synaptic vacuoles forming a pair of vacuoles which are in mutual contact. Extensions from three to four synaptic bodies belonging to the β-cell type enter into contact relation to each α-cell and the dendrites which are synaptically connected to the α-cell. These contacts are interpreted as synaptic contacts. It is proposed that this extensive system of interreceptor contacts might exert inhibitory effects on the transmission between α-cells and bipolars.

The Clinical Physiology of the Lungs

The author has brought together in this monograph material comprising originally a series of lectures, extended and amplified with the work of others. Discussion is organized around the basic structural components of the lung—arteries, veins, capillaries, bronchi and bronchioles, nerves, and lymphatics. The physiology of these is dealt with in broad outlines, allowing the author to lead the discussion smoothly from basic facts to current theory. His familiarity with the subject enables him to maintain the integration of the known facts, while disclosing the large questions which still remain, in an informal and provocative fashion.