Fibrous nuclei

If crystallisation occurs in an oriented melt, then non-spherulitic microstructures can form, with preferred orientation of the crystals (Section 3.4.10). Fibrous nuclei, believed to contain fully extended polymer chains, can form in an oriented melt. Figure 6.7a shows several fibrous nuclei, in a polyethylene injection moulding, aligned with the flow direction. On either side of these dark nuclei is a bright layer, where lamellar crystals have grown from the nucleus. The c axes of the lamellar crystals are parallel to the fibrous nucleus the microstructure of platelet crystals skewered by a rod-like nucleus has been described as a shish kebab. The rest of the microstructure consists of small spherulites. 

Polarised light micrographs of (a) Fibrous nuclei in a polyethylene injection moulding surrounded by parallel lamellar crystals, then by spherulites. (b) Oriented skin of a polypropylene moulding, forming the hinge of a box where there is a thickness restriction. 

The nucleus contains bundles of a fibrous material known as chromatin, which is made up of mixed proteins and deoxyribonucleic acid (DNA), the substance that carries the genetic information of the living organism of which the cell is a component. All cells replicate by division. When a cell replicates, DNA in the chromatin of the nucleus passes the genetic information from one generation to the next one. As the cell divides, the chromatin clusters into rodlike structures known as chromo-... 

When the surface of the purified HeLa cell nucleus is observed by AFM (Fig. 5a), relatively smooth surface is seen, although many small projections and cavities can be identified (Fig. 5b). When the isolated nuclei are successively subjected to the detergent treatment and high-salt treatment on the glass substrate to remove the nuclear membrane and nucleoplasm, fibrous structures appear (Fig. 5c, d). A close examination by AFM classified the existence of granular structures ( 80 nm width)... 

It has been assumed that the nucleus contains an immobile structure , in which chromatin fibers are partially attached and fixed. These structures are called nuclear matrix or nuclear scaffold . When cells are successively treated with detergent, high-salt solution and DNase I, the nuclear scaffold can be observed as a fibrous network in the cell nucleus (Fey et al, 1986 Nickerson, 2001 Yoshimura et al, 2003) (Fig. 2b). The biochemical analyses of the nuclear scaffold have identified a 174kDa protein as a major component (Fisher et al, 1982). This protein is now known as topo II (Berrios et al, 1985). 

Fig. 1. (opposite page) Distribution of FITC-conjugated BSA in various fibroblast cell lines under different fixation/permeabilization regimes. (A-D) Protein distribution in living cells (A) PtKj, (B) CHO, (C) 3T3, and (D) HeLa cells. The protein is excluded from the nuclei of all cells. (E-H) Protein distribution in cells extracted for 10 min with 0.1% Triton X-100 before fixation for 30 min with 3.7% formaldehyde (E) PtKi, (F) CHO, (G) 3T3, and (H) HeLa cells. Nuclear fluorescence is seen in (E) PtKj and (G) 3T3 cells. (I-L) Protein distribution in cells extracted for 10 min with 1% Triton X-100 before fixation for 30 min with 3.7% formaldehyde (I) PtKj, (J) CHO, (K) 3T3, and (L) HeLa cells. No fluorescence is detected in the cells with the exception of some nuclear fluorescence seen in (L) HeLa cells. (M-P) Protein distribution in cells fixed for 30 min with 3.7% paraformaldehyde before permeabilization for 10 min with 0.1% Triton X-100. Fluorescence is seen primarily in the cytoplasm with the exception that nuclear fluorescence is seen in (M) PtKi and (N) CHO cells. (Q-T) Protein distributions in cells fixed for 5 min with 90% methanol, 50 vaM EGTA at -20°C (Q) PtKj, (R) CHO, (S) 3T3, and (T) HeLa cells. All cells show an overall low fluorescence, fibrous-textured cytoplasmic fluorescence, and bright staining at the periphery of the nucleus. 10 mm per scale division (black bar). (Reproduced with permission from ref. 6.)... 

Anyone eating a steak or a slice carved from roast beef knows that meat is fibrous in texture. These fibers, 20 to 100 fj.m in diameter and very long, are the multinucleate muscle cells of which skeletal muscles are composed (Fig. 1 A, B). Such fibers in the light microscope appear cross-striated and the muscles from which they are derived are known as striated muscles. The term striated also covers the muscles in animal hearts (Fig. 1C), but here the cells (the myocytes) are much shorter, they contain a single nucleus, and they are linked end to end by special structures known as... 

Most of the filaments in basal cells lie perpendicular to the skin surface, but in the stratum spinosum they gradually shift into a perinuclear network (31, 64). The above concept is diagrammed in Figure 10. As cells become fiattened, the radial pattern of filaments about the nucleus (31, 34) is preserved but the keratinized fibers come to lie parallel with the skin surface, like spokes in a bicycle wheel (31, 64). Collapse of the fibrous cage produces tension on desmosomes and deforms the cell envelope so that, the deep interdigitations formed between... 

This arrangement explains Brody s (31) observation that, Tono-fibrils form concentric rings around the nucleus. The tonofibrils anastomose within these rings and from ring to ring, and also show connections with the fibrous part of the desomosomes. ... 

The DNA-containing nucleus has been described as a balloon filled with thick solution with a fibrous mesh which holds the DNA in place and which moves molecules about. 

The nucleus (Figure 2.15) consists of nucleoplasm surrounded by a nuclear envelope. The nucleoplasm is a material rich in DNA in which proteins called lamins form a fibrous network that provides structural support. A prominent feature of the nucleoplasm is a network of chromatin fibers composed of DNA and DNA packaging proteins known as the histones. The DNA is believed to be attached to the lamins. The nuclear envelope is composed of two membranes that fuse at structures called nuclear pores. The outer nuclear membrane is continuous with the rough endoplasmic reticulum. The nuclear pores (Figure 2.16) are relatively... 

The Nucleus Contains the DNA Genome, RNA Synthetic Apparatus, and a Fibrous Matrix... 

The role chitin as a material of highly ordered crystalline structure has been reported in the study [96]. X-ray diffraction analysis was carried out in order to find the changes of the crystalline structure upon the substitution reaction with NCO terminated prepolymer. The X-ray diffraction studies showed that crystallinity mainly depends on the concentration of chitin in the polyurethane backbone, crystallinity increased as the concentration of chitin into the final PU increased (Fig. 3.22). The crystallinity of some polymers was clearly observed by optical microscopic studies [114]. The results of X-ray diffraction experiments correlate with optical microscopy findings. A crystalline polymer is distinguished from an amorphous polymer by the presence of sharp X-ray Unes superimposed on an amorphous halo. Under an optical microscope, the presence of polycrystalline aggregates appear as spherulites [114]. The spheruhtes are made of small crystallites and grow Irom a nucleus at their centre. They consist of narrow chain folded lamellae growing radially. Since the fibrous crystals are radial, the chains folded with the lamellae are circumferentially oriented. From the evaluation of the X-ray and optical microscopic studies, it has been observed that the involvement of chitin in the PU formulation and have improved crystallinity of the final polyurethane. 

The foam cells then form deposits of fat in the intima and media of the blood vessel wall, which are called fatty streaks the early form of plaques. This initiates an inflammatory process, as a result of which even more monocytes are recruited into the sub-intimal space. The proliferation of the smooth muscle cells leads to the thickening of the blood-vessel wall, accumulation of more lipids, and development of a lipid-necrotic nucleus, which is covered with fibrous tissue, forming the fibrous cap of a plaque. The narrowing of the vessel can remain unnoticed by the patient for many years. However, in the course of time, a stable plaque can also become unstable, when activated cells within the plaque secrete matrix proteases, which degrade the fibrous cap (Fig. 5.148). This leads within minutes to rupture and thrombus formation, causing occlusion of blood-vessels and resulting in a heart attack, unstable angina pectoris or a stroke. 

Fartasch et al. 1993). Apparently, immediately after this process the nucleus and the cytoplasmic nucleic acids are disintegrated, the cell membrane is exchanged for a protein envelope, and the resulting corneocyte contains essentially only the fibrous keratin. In fact, this process is so fast that it has not yet been recorded by TEM. 

Aromatic term applied to a group of hydrocarbons characterized by the presence of the benzene nucleus a major series of unsaturated cyclic hydrocarbons whose carbon atoms are arranged in closed rings Asbestos fibrous magnesium silicate... 

---