Cytosol

 At one time, it was believed that the cytoplasm intervening between the discrete organelles and deposits was unstructured. This belief was reinforced by the use of homogenization and centrifugation of the homogenates to yield fractions consisting of recognizable membrane-bound organelles. The final supernatant produced by this process, after the separation of organelles, is called the cytosol. The cytosol constitutes about half the total volume of the cell. Homogenization of cells disrupts a delicate microtrabecular lattice that incorporates filaments of actin, microtubules, intermediate filaments, enzymes, and other soluble constituents into a structured cytosol. The cytosol coordinates the intracellular movements of organelles and provides an explanation for the viscosity of the cytoplasm. Soluble (not membrane-bound) enzymes, such as those of the glycolytic pathway, for example, function more efficiently when organized in a sequence instead of having to rely on random collisions with their substrates. The cytosol provides a framework for this organization. It contains thousands of enzymes that produce building blocks for larger molecules and break down small molecules to liberate energy. All machinery to synthesize proteins (rRNA, mRNA, tRNA, enzymes, and other factors) is contained in the cytosol.

Cell Components & Diseases

Many diseases are related to molecular alterations in specific cell components. In several of these diseases, structural changes can be detected by light or electron microscopy or by cytochemical techniques. Table 2–5 lists some of these diseases and emphasizes the importance of understanding the many cell components in pathobiology. Table 2–5. Some Human and Animal Diseases Related to Altered Cellular Components. Cell Component Involved Disease Molecular Defect Morphological Change Clinical Consequence Mitochondrion Mitochondrial cytopathy Defect of oxidative phosphorylation Increase in size and number of muscle mitochondria High basal metabolism without hyperthyroidism Microtubule Immotile cilia syndrome Lack of dynein in cilia and flagella Lack of arms of the doublet microtubules Immotile cilia and flagella with male sterility and chronic respiratory infection Mouse (Acomys) diabetes   Reduction of tubulin in pancreatic cells Reduction of microtubules in cells High blood sugar content (diabetes) Lysosome Metachromatic leukodystrophy Lack of lysosomal sulfatase Accumulation of lipid (cerebroside) in tissues Motor and mental impairment Hurler disease Lack of lysosomal -L-iduronidase  Accumulation of dermatan sulfate in tissues Growth and mental retardation Golgi complex I-cell disease Phosphotransferase deficiency Inclusion-particle storage in several cells Psychomotor retardation, bone abnormalities

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