The human organism presents about 200 different cell types. During the cell differentiation, the cells synthesize specific proteins, change their shape, andbecome very efficient in specialized functions.
The cell is composed of two basic parts: cytoplasm and nucleus. Cytoplasmic components are usually not clearly distinguishable incommon hematoxylin and eosin stained preparations. The cytoplasm itself is composed of a fluid component (cytosol) in which are contained metabolically active structures, the organelles, which can bemembranous or non-membranous protein complexes. The shape and motility of eukaryotic cells are determined by components of the cytoskeleton. The cytosol contains hundreds of enzymes, such as those ofthe glycolytic pathway, that produce building blocks for larger molecules and break down small molecules to liberate energy.
Eukaryotic cells are enveloped by a limiting membranecomposed of phospholipids, cholesterol, proteins and chains of oligosaccharides covalently linked to phospholipid and protein molecules. The membrane functions as a selective barrier that regulatesthe passage of certain materials into and out the cell. One important role of the membrane is to keep constant the ion content of cytoplasm.
Endocytosis involves folding and fusion ofthis membrane to form vesicles which enclose the material transported. Cells show three general types of endocytosis: a) phagocytosis, b) fluid-phase endocytosis, c) receptor-mediated endocytosis.Exocytosis
In exocytosis a membrane-limited Cytoplasmic vesicle fuses with the plasma membrane. The fusion of membranes during exocytosis is a highly regulated process involving interactions betweenseveral specific membrane proteins.
Mitochondria are membrane-enclosed organelles with enzyme arrays specialized for aerobic respiration and production of ATP, which contains...