Terms
- Actin
- A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.
- Aminopeptidase
- An enzyme found within the small intestine that splits off one amino acid at a time, beginning at the opposite end of the polypeptide containing a free carboxyl group.
- Basal Body
- A eukaryotic cell organelle consisting of a 9 + 0 arrangement of microtubule triplets; may organize the microtubule assembly of a cilium or flagellum; structurally identical to a centriole.
- Cell Fractionation
- The disruption of a cell and separation of its organelles by centrifugation.
- Cell Wall
- A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. In plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid and is the primary constituent of wood.
- Central Vacuole
- A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development.
- Centriole
- A structure in an animal cell composed of cylinders of microtubule triplets arranged in a 9 + 0 pattern. An animal cell usually has a pair of centrioles involved in cell division.
- Centrosome
- Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center.
- Chloroplast
- An organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.
- Chromatin
- The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing, chromatin exists as a mass of very long, thin fibers that are not visible with a light microscope.
- Chromosome
- A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.
- Cilium
- A short cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of plasma membrane.
- Collagen
- A glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom.
- Contractile Vacuole
- A membranous sac that helps move excess water out of the cell.
- Crista
- (plural, cristae) An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP.
- Cytoplasm
- The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.
- Cytoplasmic Streaming
- A circular flow of cytoplasm, involving myosin and actin filaments, that speeds the distribution of materials within cells.
- Cytoskeleton
- A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions.
- Cytosol
- The semifluid portion of the cytoplasm.
- Desmosome
- A type of intercellular junction in animal cells that functions as an anchor.
- Dynein
- A large contractile protein forming the side-arms of microtubule doublets in cilia and flagella.
- Electron Microscope (EM)
- A microscope that focuses an electron beam through a specimen, resulting in resolving power a thousandfold greater than that of a light microscope. A transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning electron microscope (SEM) is used to study the fine details of cell surfaces.
- Endomembrane System
- The collection of membranes inside and around a eukaryotic cell, related either through direct physical contact or by the transfer of membranous vesicles.
- Eukaryotic Cell
- A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles, present in protists, plants, fungi, and animals; also called eukaryote.
- Extracellular Matrix (ECM)
- The substance in which animal tissue cells are embedded, consisting of protein and polysaccharides.
- Fibronectin
- A glycoprotein that helps cells attach to the extracellular matrix.
- Flagellum
- (plural, flagella) A long cellular appendage specialized for locomotion. The flagella of prokaryotes and eukaryotes differ in both structure and function.
- Food Vacuole
- A membranous sac formed by phagocytosis.
- Gap Junction
- A type of intercellular junction in animal cells that allows the passage of material or current between cells.
- Glycoprotein
- A protein covalently attached to a carbohydrate.
- Golgi Apparatus
- An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum.
- Granum
- (plural, grana) A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis.
- Integrin
- A receptor protein built into the plasma membrane that interconnects the extracellular matrix and the cytoskeleton.
- Intermediate Filament
- A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments.
- Light Microscope (LM)
- An optical instrument with lenses that refract (bend) visible light to magnify images of specimens.
- Lysosome
- A membrane-enclosed sac of hydrolytic enzymes found in the cytoplasm of eukaryotic cells.
- Microfilament
- A solid rod of actin protein in the cytoplasm of almost all eukaryotic cells, making up part of the cytoskeleton and acting alone or with myosin to cause cell contraction.
- Microtubule
- A hollow rod of tubulin protein in the cytoplasm of all eukaryotic cells and in cilia, flagella, and the cytoskeleton.
- Middle Lamella
- A thin layer of adhesive extracellular material, primarily pectins, found between the primary walls of adjacent young plant cells.
- Mitochondrial Matrix
- The compartment of the mitochondrion enclosed by the inner membrane and containing enzymes and substrates for the Krebs cycle.
- Mitochondrion
- (plural, mitochondria) An organelle in eukaryotic cells that serves as the site of cellular respiration.
- Myosin
- A type of protein filament that interacts with actin filaments to cause cell contraction.
- Nuclear Envelope
- The membrane in eukaryotes that encloses the nucleus, separating it from the cytoplasm.
- Nuclear Lamina
- A netlike array of protein filaments that maintains the shape of the nucleus.
- Nucleoid
- A dense region of DNA in a prokaryotic cell.
- Nucleolus
- (plural, nucleoli) A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes.
- Nucleus
- (1) An atom’s central core, containing protons and neutrons. (2) The chromosome-containing organelle of a eukaryotic cell. (3) A cluster of neurons.
- Organelle
- One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells.
- Peroxisome
- A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.
- Phagocytosis
- A type of endocytosis involving large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells.
- Plasma Membrane
- The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell’s chemical composition.
- Plasmodesma
- (plural, plasmodesmata) An open channel in the cell wall of plant through which strands of cytosol connect from an adjacent cell.
- Plastid
- One of a family of closely related plant organelles that includes chloroplasts, chromoplasts, and amyloplasts (leucoplasts).
- Primary Cell Wall
- A relatively thin and flexible layer first secreted by a young plant cell.
- Prokaryotic Cell
- A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea.
- Proteoglycan
- A glycoprotein in the extracellular matrix of animal cells, rich in carbohydrate.
- Pseudopodium
- (plural, pseudopodia) A cellular extension of amoeboid cells used in moving and feeding.
- Ribosome
- A cell organelle constructed in the nucleolus and functioning as the site of protein synthesis in the cytoplasm; consists of rRNA and protein molecules, which make up two subunits.
- Rough ER
- That portion of the endoplasmic reticulum studded with ribosomes.
- Scanning Electron Microscope (SEM)
- A microscope that uses an electron beam to scan the surface of a sample to study details of its topography.
- Secondary Cell Wall
- A strong and durable matrix often deposited in several laminated layers for plant cell protection and support.
- Smooth ER
- That portion of the endoplasmic reticulum that is free of ribosomes.
- Stroma
- The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.
- Thylakoid
- A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.
- Tight Junction
- A type of intercellular junction in animal cells that prevents the leakage of material between cells.
- Tonoplast
- A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the vacuolar contents, called cell sap; also known as the vacuolar membrane.
- Transmission Electron Microscope (TEM)
- A microscope that passes an electron beam through very thin sections; primarily used to study the internal ultrastructure of cells.
- Transport Vesicle
- A tiny membranous sac in a cell’s cytoplasm carrying molecules produced by the cell.
- Vesicle
- A sac made of membrane inside of cells.
