Carbohydrates layers

The lamellar structure of saccharide-peptide block copolymers presents many analogies with the structure of copolymers with a hydrophobic polyvinyl block and a hydrophobic polypeptide block and exhibits a similar behaviour as a function of the solvent concentration. When the solvent concentration increases the total thickness of a sheet and the thickness of the carbohydrate layer both increase while the thickness of the polypeptide layer remains nearly constant284. ... 

The thickness of the carbohydrate layer is nearly independant of the copolymer composition while the thickness of the polypeptide layer increases linearly with the molecular weight of the polypeptide block285. ... 

The study by low-angle X-ray diffraction of these mesophases provides X-ray patterns exhibiting a set of sharp lines with Bra spadi characteristic of a layered structure. This lamellar structure results from the superposition of plane, parallel, and equidistant sheets each sheet contains two layers one of thickness d formed by the carbdiydrate blocks, the other of thickness dg formed by the polypeptide blocks, there is a partition of the solvent between the two blocks 70% DMSO is localized in the carbohydrate layer Furthermore, the polypeptide chains are in a a-helix conformation as is demonstrated by infrared specttoscopy and X-ray diffraction and are oriented perpendicular to the plane of the sheets and assembled in a bidimensional hexagonal lattice as is revealed by X-rays ... 

Some of the proteins and lipids on the external surface of the membrane contain short chains of carbohydrates (oligosaccharides) that extend into the aqneons medium. Carbohydrates therefore constitute 2 to 10% of the weight of plasma membranes. This hydrophilic carbohydrate layer, called the glycocalyx, protects the cell against digestion and restricts the nptake of hydrophobic componnds. 

The effect of the solvent concentration on the geometrical parameters of the lamellar structure is similar for all the copolymers studied and is illustrated in Fig. 1 for the copolymer 0 EB.33 which contains 62 % of polypeptide. When the DNSO concentration increases the total thickness d of a sheet increases, the thickness dA of the carbohydrate layer also increases, while the thickness ds of the polypeptide layer remains nearly constant. 

Total thickness d of a sheet (A) thickness cIa of the carbohydrate layer (O) thickness di3 of the peptide layer (6). 

Recently periderm layers from the bark of several species of trees were ultra-structurally characterized. Suberin deposition appeared to immediately precede the deposition of a tertiary carbohydrate layer during the formation of cork cells in the bark of Acacia Senegal (477). A tertiary carbohydrate layer overlaying the suberin lamellae was also seen in the periderm of Acorus calamus, but not in the suberized periderms of Larix decidua or Picea abies (478, 482). It is possible that... 

Molisch s Test. Dissolve about 01 g. of the carbohydrate in z ml. of water (for starch use 2 ml. of starch solution ), add 2-3 drops of a 1 % alcoholic solution of i-naphthol (ignoring traces of the latter precipitated by the water) and then carefully pour 2 ml. of cone. H2SO4 down the side of the test-tube so that it forms a heavy layer at the bottom. A deep violet coloration is produced where the liquids meet. This coloration is due apparently to the formation of an unstable condensation product of i-naphthol with furfural (an aldehyde produced by the dehydration of the carbohydrate). 

Chemical Constituents of Cell Wall. Variation in chemical composition across the cell wall is also shown in Figure 6. The principal constituents of cellulose, hemicellulose, and lignin are present throughout the cell wall but in different proportions. Cellulose is not present in the interfiber middle lamella, which is virtually all lignin. The layer is essentially all carbohydrates (qv), especially hemiceUuloses, having Uttie or no lignin. 

Air pollutants may enter plant systems by either a primary or a secondary pathway. The primary pathway is analogous to human inhalation. Figure 8-2 shows the cross section of a leaf. Both of the outer surfaces are covered by a layer of epidermal cells, which help in moisture retention. Between the epidermal layers are the mesophyll cells—the spongy and palisade parenchyma. The leaf has a vascular bundle which carries water, minerals, and carbohydrates throughout the plant. Two important features shown in Fig. 8-2 are the openings in the epidermal layers called stomates, which are controlled by guard cells which can open and close, and air spaces in the interior of the leaf. 

Extracellular matrix The surfaces of animal cells are covered with a flexible and sticky layer of complex carbohydrates, proteins, and lipids. This complex coating is cell-specific, serves in cell-cell recognition and communication, creates cell adhesion, and provides a protective outer layer. 

Bacillus anthracis, the causative organism of anthrax, possesses a capsule composed of polyglutamic acid the slime layers produced by other organisms are of a carbohydrate nature. 

The lower rates of nutrient absorption associated with diets high in nonstarch polysaccharides are probably due to the increased viscosity of digesta (Vaugelade et al., 2000), which increases the thickness of the unstirred layer overlying the enterocytes and causes anon-specific decline in solute absorption. This explains why diets high in 3-glucans, which are structural carbohydrates and which increase viscosity of digesta, reduce absorption of nutrients and... 

LAYER P, RIZZA R A, ZINSMEISTER A R, CARLSON G L, DIMAGNO E P (1986) Effect of a purified amylase inhibitor on carbohydrate tolerance in normal subjects and patients with diabetes mellitus . Mayo Clin Proc. 61 442-7. 

Wing, R.E. and BeMiller, J.N., Preparative thin layer chromatography, in Methods in Carbohydrate Chemistry, Whistler, R.L. and BeMiller, J.N., Eds., Academic Press, New York, 1972, pp. 60-64. 

As has already been stated, Weibull reported the flagella of P. vulgaris to be composed of 98 per cent protein. This contradicts Pijper s statement that flagella are formed from the carbohydrate slime layer that is peeled off into a number of thin, wavy threads. 

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