The membranous organelles include:  the plasma (cell) membrane, a lipid bilayer that forms the cell boundary as well as the boundaries of many organelles within the cell; rough-surfaced endoplasmic reticulum (rER), a region of endoplasmic reticulum associated with ribosomes and the site of protein synthesis and modification of newly synthesized proteins;  smooth-surfaced endoplasmic reticulum (sER), a region of endoplasmic reticulum involved in lipid and steroid synthesis but not associated with ribosomes; Golgi apparatus, a membranous organelle composed of multiple ﬂattened cisternae responsible for modifying, sorting, and packaging proteins and lipids for intracellular or extracellular transport;  endosomes, membrane-bounded compartments interposed within endocytotic pathways that have the major function of sorting proteins delivered to them via endocytotic vesicles and redirecting them to different cellular compartments for their final destination;  lysosomes, small organelles containing digestive enzymes that are formed from endosomes by targeted delivery of unique lysosomal membrane proteins and lysosomal enzymes;  transport vesicles—including pinocytotic vesicles, endocytotic vesicles, and coated vesicles—that are involved in both endocytosis and exocytosis and vary in shape and the material that they transport;  mitochondria, organelles that provide most of the energy to the cell by producing adenosine triphosphate (ATP) in the process of oxidative phosphorylation; and  peroxisomes, small organelles involved in the production and degradation of H2O2 and degradation of fatty acids.
The nonmembranous organelles include:  microtubules, which together with actin and intermedi ate filaments form elements of the cytoskeleton and continuously elongate (by adding tubulin dimers) and shorten (by removing tubulin dimers), a property referred to as dynamic instability;  flaments, which are also part of the cytoskeleton and can be classified into two groups—actin flaments, which are ﬂexible chains of actin molecules, and intermediate flaments, which are ropelike fibers formed from a variety of proteins—both groups providing tensile strength to withstand tension and confer resistance to shearing forces;  centrioles, or short, paired cylindrical structures found in the center of the microtubule-organizing center (MTOC) or centrosome and whose derivatives give rise to basal bodies of cilia; and  ribosomes, structures essential for protein synthesis and composed of ribosomal RNA (rRNA) and ribosomal proteins (including proteins attached to membranes of the rER and proteins free in the cytoplasm).
An outline of the key features of cellular organelles and inclusions is provided in Table 2.1. The normal function and related pathologies of the organelles are summarized in Table 2.2.