| Cell Part: | Structure: | Functions: |
| Plasma membrane | Membrane composed of a double layer of lipids (phospholipids, cholesterol) within which proteins are embedded; proteins may extend entirely through the lipid bilayer or protrude on only one face; externally facing proteins and some lipids have attached sugar groups | Serves as an external cell barrier; acts in transport of substances into or out of the cell; externally facing proteins act as receptors (for hormones, neurotransmitters) and in cell-to-cell recognition |
| Cytoplasm | Cellular region between the nuclear and plasma membranes; consists of fluid cytosol, containing dissolved solutes, inclusions (stored nutrients, pigments granules), and organelies, the metabolic machinery of the cytoplasm. |
| Cytoplasmic organelles |
| −Mitochondria | Rod-like, double-membrane structures; inner membrane folded into projections called cristae | Site of ATP synthesis; powerhouse of the cell |
| −Ribosome's | Dense particles consisting of two subunits, each composed of ribosomal RNA and proteins; free or attached to rough ER | The sites of protein synthesis |
| −Rough endoplasmic reticulum | Membrane system enclosing a cavity, the cistern a, and coiling through the cytoplasm; externally studded with ribosome's | Makes proteins that are secreted from the cell; makes the cell's membrane |
| −Smooth endoplasmic reticulum | Membranous system of tubules; free of ribosomes | Site of lipid metabolism |
| −Golgi apparatus | A stack of smooth membrane sacs close to the nucleus | Packages, modifies, and segregates proteins for secretion from the cell and inclusion in lysosomes; sends membranes from rough ER to their destinations |
| −Lysosomes | Membranous sacs containing acid hydrolases | Sites of intracellular digestion |
| −Peroxisomes | Membranous sacs of oxidase enzymes | The enzymes detoxify a number of toxic substances; the most important enzyme, catalase, breaks down hydrogen peroxide |
| −Microfilaments | Fine filaments of the contractile protein actin | Involved in muscle contraction and other types of intracellular movement; help form the cell's cytoskeleton |
| −Intermediate filaments | Protein fibres; composition varies | The stable cytoskeleton elements; resist tensile forces acting on the cell |
| −Microtubles | Cylindrical structures composed of tubulin proteins | Support the cell and give it shape; involved in intracellular and cellular movements, form centrioles |
| −Centrioles | Paired cylindrical bodies, each composed of nine triplets of microtubules | Organise a microtubule network during mitosis to form the spindle; form bases of cilia and flagella |
| Nucleus | Surrounded by the nuclear membrane; contains fluid nucleoplasm, nucleoli, and chromatin | Control center of the cell; responsible for transmitting genetic information and providing the instructions for protein synthesis |
| −Nuclear membrane | Double bilipid membrane containing proteins; pierced by pores; continuous with the cytoplasmic ER | Separates the nucleoplasm from the cytoplasm and regulates passage of substances to and from the nucleus |
| −Nucleoli | Dense spherical (non-membrane-bounded) bodies | Site of ribosome subunit manufacture |
| −Chromatin | Granular, threadlike material composed of DNA and histone proteins | |
| Source: Marieb, EN and Mallat, J. Human Anatomy. 2nd ed. Menlo Park, Calif.: Benjamin Cummings, c1997. |
