Cell Organelle Terms


Cell inclusions: Insoluble storage materials or metabolic products found in the cytoplasm of a cell, such as glycogen, fat, pigment granules, or crystals.


Centrioles: Paired cylindical bodies near the nucleus; form the bases of cilia and flagella; they divide and organize spindle fibers during mitosis and meiosis.


Centrosome: Microtubule organizing center of cells; contains two centrioles.


Chromatids: The two strands of DNA formed by duplication of a chromosome that are joined by a centromere; they condense and become visible under a light microscope during mitosis and meiosis.


Chromatin: Thread-like form of the chromosomes in the nucleus during interphase.


Chromosomes: DNA with associated proteins; contains genes (hereditary factors).


Cilia: Short motile processes, composed of microtubules; propels material across the cell surface; abundant in cells that line the respiratory tract.


Cytoplasm: All of the material between the plasma membrane and nucleus.


Cytoskeleton: Cell skeleton; network of fibrous proteins; provides cell support and organelle movement.


Cytosol: Viscous fluid portion of the cytoplasm in which the organelles are suspended.


Flagellum: A long whip-like projection, composed of microtubules; propels the sperm cell.


Golgi apparatus: Flattened membranous sacs; packages proteins into vesicles for secretion, modifies proteins that become part of cell membranes, and packages enzymes into lysosomes; abundant in secretory cells. Also called Golgi complex.


Intermediate filaments: Cytoskeletal element composed of rope-like assemblies of fibrous proteins; provide support and strength to cells; act as internal "guy wires"; help form desmosomes.


Lysosome: Vesicle containing strong digestive enzymes; originates from the Golgi apparatus; abundant in phagocytes.


Microfilaments: Cytoskeletal element composed of thin strands of the contractile protein actin; helps produce and maintain cell shapes; helps move cell organelles; forms core of microvilli.


Microtubules: Cytoskeletal element composed of hollow tubes made of the protein tubulin; determines cell shape and movement of organelles; component of cilia, flagella and spindle fibers.


Microvilli: Tiny hairlike extensions of cell membranes, organized around microfilaments; greatly increase the surface area of absorptive cells; abundant in cells that line the GI tract.


Mitochondrion: Powerhouse of the cell; rod-shaped organelle bounded by two membranes; produces ATP by aerobic cellular respiration; abundant in muscle cells.


Nuclear envelope: Double membrane surrounding the cell nucleus; contains large nuclear pores.


Nuclear pore: Octagonal opening in the nuclear envelope where the two nuclear membranes are in contact; produced by proteins that regulate the transport of materials between the nucleus and the cytoplasm.


Nucleolus: Round dense body in the cell nucleus where the ribosomal subunits are synthesized.


Nucleoplasm: Contents of the cell nucleus other than the chromatin and nucleoli.


Nucleus: Control center of the cell; contains genetic material; surrounded by a double membrane.


Organelle: Any structure within a cell that performs specialized metabolic functions.


Peroxisome: Vesicle that detoxifies poisonous molecules and participates in metabolic oxidations involving hydrogen peroxide; abundant in liver cells.


Phagolysosome: Vesicle formed by the fusion of a phagosome with a lysosome, in which digestion of the phagocytized particles occur.


Phagosome: Endocytotic vesicle formed by phagocytosis.


Plasma membrane: Outer cell membrane composed of phospholipid bilayer with embedded proteins, cholesterol and surface polysaccharides; encloses cell contents and regulates entry and exit of materials.


Proteasome: Tiny barrel-shaped protein complex (smaller than a ribosome) with proteases that degrade endogenous proteins that have been marked by binding to ubiquitin.


Ribosome: Tiny organelle that is the site of protein synthesis; complex of rRNA and proteins that uses mRNA as a template during translation; exists as two subunits (40S and 60S) that join together (80S) when bound to mRNA.


Rough endoplasmic reticulum (rER): Flattened membranous sacs that are continuous with the outer nuclear membrane; contains attached ribosomes, synthesizes proteins and transports them to other sites in the cell; attaches carbohydrates to glycoproteins; synthesizes phospholipids.


Smooth endoplasmic reticulum (sER): Membranous tubules continuous with the rough endoplasmic reticulum; performs metabolism of lipids, steroids, carbohydrates, and drugs.


Vesicle: Membranous sacs in the cytoplasm that may be used in the transport, storage, digestion, or chemical modification of substances.