Archive | Biology

Cytoplasmic filaments are elongate, un-branched, proteinaceous strands that consist of bundles or groups of protein molecules sometimes wound into a helical shape. Although organized arrays of cytoplasmic fila­ments were first described for muscle cells and have been most extensively studied in this tissue, it is now apparent that essentially all eukaryotic cells contain these filaments. Cytoplasmic filaments can be subdi­vided [...]

1. Pinocytosis: Using time-lapse photography to study tissue culture cells, W. H. Lewis in 1931 described what seemed to be a curious phenomenon in which small amounts of culture medium were trapped in invaginations of the plasma membrane and then pinched off to form small cytoplasmic vesicles. Because the entire process ap­peared much like some form of organized cell drink­ing, [...]

Over the years, a number of sophisticated analytical and preparative techniques have been developed for separating, analyzing, and isolating the various macromolecular constituents of cells and tissues. Various forms of electrophoresis, chromatography, and ultracentrifugation are now in routine use in most lab­oratories engaged in molecular biological studies and have greatly increased our understanding of the chem­istry and properties of the [...]