OVERVIEW OF THE CELL AND CYTOPLASM / 22 MEMBRANOUS ORGANELLES / 25 Plasma Membrane / 25 Endosomes / 35 Lysosomes / 38 Autophagy / 41 Proteasome-Mediated Degradation / 44 Rough-Surfaced Endoplasmic Reticulum / 45 Smooth-Surfaced Endoplasmic Reticulum / 49 Golgi Apparatus / 50 Mitochondria / 53 Peroxisomes (Microbodies) / 56 NONMEMBRANOUS ORGANELLES / 56 Microtubules / 56 Actin Filaments / 59 Intermediate Filaments / 62 Centrioles and Microtubule-Organizing Centers / 65 Basal Bodies / 71 INCLUSIONS / 71 CYTOPLASMIC MATRIX / 73 Folder 2.1 Clinical Correlation: Lysosomal Storage Diseases / 42 Folder 2.2 Clinical Correlation: Abnormalities in Microtubules and Filaments / 68 Folder 2.3 Clinical Correlation: Abnormal Duplication of Centrioles and Cancer / 72
Cells are the basic structural and functional units of all multicellular organisms.
The processes we normally associate with the daily activities of organisms—protection, ingestion, digestion, absorption of metabolites, elimination of wastes, movement, reproduction, and even death—are all reﬂections of similar processes occurring within each of the billions of cells that constitute the human body. To a very large extent, cells of different types use similar mechanisms to synthesize protein, transform energy, and move essential substances into the cell. They use the same kinds of molecules to engage in contraction, and they duplicate their genetic material in the same manner.
Specific functions are identified with specific structural components and domains within the cell.
Some cells develop one or more of these functions to such a degree of specialization that they are identified by the function and the cell structures associated with them. For example, although all cells contain contractile filamentous proteins, some cells such as muscle cells, contain large amounts of these proteins in specific arrays. This allows them to carry out their specialized function of contraction at both the cellular and tissue level. The specialized activity or function of a cell may be reﬂected not only by the presence of a larger amount of the specific structural component performing the activity but also by the shape of the cell, its organization with respect to other similar cells, and its products (Fig. 2.1).
Cells can be divided into two major compartments: the cytoplasm and the nucleus.
In general, the cytoplasm is the part of the cell located outside the nucleus. The cytoplasm contains organelles (“little organs”) and inclusions in an aqueous gel called the cytoplasmic matrix. The matrix consists of a variety of solutes, including inorganic ions (Na , K , Ca2 ) and organic molecules such as intermediate metabolites, carbohydrates, lipids, proteins, and RNAs. The cell controls the  concentration