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Actin  -  A very abundant protein in eukaryotic cells that is the main component of actin filaments.
Actin Filaments  -  Approximately 5-9 nanometers in diameter. Provide structural support to the plasma membrane. As a cytoskeletal protein provides for movement of organelles within cells.
Centromere  -  A round structure that holds together sister chromatids.
Centrosome  -  A region of the cell near the nucleus from which microtubules sprout. Centrosomes are not found in all cells. Centrosomes are comprised of two centrioles.
Chromosome  -  A structure composed of DNA and proteins containing all the genetic material of a cell. Found in the cell nucleus.
Cytoplasm  -  A fluid found in the main compartment of eukaryotic cells. Includes everything outside the cell nucleus but the organelles and the cytoskeleton. The main component is cytosol.
Cytoskeleton  -  A system of protein filaments found throughout the cytoplasm of eukaryotic cells that help provide for cell structure. Composed of actin, intermediate filaments, and microtubules.
Cytosol  -  The main component of the cytoplasm that fills the main compartment of eukaryotic cells.
Endoplasmic reticulum  -  A membrane-bound organelle found in eukaryotic cells. Makes direct contact with the cell nucleus and, since it is dotted with ribosomes, is the site of lipid and protein synthesis. Comes in two forms, smooth and rough.
Endosome  -  A membrane-bound organelle found in eukaryotic cells. Responsible for delivering molecules to the lysosome for digestion.
Eukaryote  -  An organism composed of one or more cells with defined intracellular components including a nucleus and cytosol. Includes all organisms except bacteria and viruses.
Golgi apparatus  -  A membrane-bound organelle found near the cell nucleus in eukaryotic cells. Responsible for sorting and packaging proteins for secretion to various destinations in the cell.
Intermediate filament  -  One of three protein components of the cytoskeleton. A fibrous protein filament approximately 10 nanometers in diameter. Forms the nuclear lamina that helps protect the cell nucleus.
Intermembrane space  -  The space between the outer and inner membrane in a mitochondria.
Lysosome  -  A membrane-bound organelle found in eukaryotic cells. Contain acids and enzymes that degrade unwanted molecules.
Matrix  -  The space inside the inner membrane of mitochondria.
Microtubule  -  One of three protein components of the cytoskeleton. Long, cylindrical structures approximately 25 nanometers in diameter. Extend from the centrosome to all parts of the cell, forming tracks on which organelles can travel within the cell. Microtubules can be either kinetocore microtubules or non-kinetocore microtubules. Kinetocore microtubules bind to sister chromatids during mitosis; non-kinetocore microtubules do not.
Mitochondria  -  An organelle within the cell. Much of cell respiration is carried out within its bounds.
Nucleus  -  A large, double membrane-bound organelle found in eukaryotic cells. Contains DNA and RNA.
Organelle  -  A membrane-bound sub-cellular structure found in eukaryotic cells. The Cell nucleus, mitochondria, ER, and golgi apparatus are all examples.
Peroxisome  -  A small, membrane-bound organelle found in eukaryotic cells. Contains oxidizing enzymes that oxidize organic molecules and process hydrogen peroxide in the cell.
Prokaryote  -  An organism composed of usually one, but occasionally more, cells that lack defined sub-cellular compartments. All essential material is enclosed within the cell membrane. Includes all bacteria and close relatives.
Ribosome  -  A molecule composed of ribosomal RNA* {biology/molecularbiology/translation}* and proteins, and located on the endoplasmic reticulum**. Responsible for mediating protein synthesis.
Rough endoplasmic reticulum  -  Endoplasmic reticulum that is coated with ribosomes and involved in protein synthesis.
Smooth endoplasmic reticulum  -  Naked endoplasmic reticulum that lacks ribosomes and is more involved in lipid synthesis.