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Definition
| A specific protein (immunoglobulin) that recognizes and binds to specific antigens; produced by plasma cells |
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| Programmed cell death; apoptosis is a normal part of an organism's development and maintenance. Compare with necrosis |
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Definition
| Structure involved in the organization and anchorage of a cilium or flagellum. Structurally similar to a centriole; each is in the form of a cylinder composed of nine triplets of microtubules (9 x 3 structure). |
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| A group of yellow to orange plant pigments synthesized from isoprene subunits; include carotenes and xanthophylls. |
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| The technique used to separate the components of cells by subjecting them to centrifugal force. See differential centrifugation and density gradient centrifugation. |
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Definition
| Mechanisms of communication between cells. Cells can signal one another with secreted signaling molecules, or a signaling molecule on one cell can combine with a receptor on another cell. Examples include the synaptic signaling of neurons and endocrine signaling. See signal transduction. |
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| The theory that the cell is the basic unit of life, of which all living things are composed, and that all cells are derived from preexisting cells. |
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| The structure outside the plasma membrane of certain cells; may contain cellulose (plant cells), chitin (most fungal cells), peptidoglycan and/or lipopolysaccharide (most bacterial cells), or other material. |
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| A structural polysaccharide composed of beta glucose subunits; the main constituent of plant primary cell walls. |
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| A device used to separate cells or their components by subjecting them to centrifugal force. |
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Definition
| One of a pair of small, cylindrical organelles lying at right angles to each other near the nucleus in the cytoplasm of animal cells and certain protist and plant cells; each centriole is in the form of a cylinder composed of nine triplets of microtubules (9 x 3 structure). |
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Definition
| A group of light-trapping green pigments found in most photosynthetic organisms. |
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| Membranous organelles that are the sites of photosynthesis in eukaryotes; occur in some plant and algal cells. |
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Definition
| The complex of DNA and protein that makes up eukaryotic chromosomes. |
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Definition
| Stacks of flattened membranous sacs that make up the Golgi complex. |
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Definition
| Shelflike or finger-like inward projections of the inner membrane of a mitochondrion. |
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Definition
| The plasma membrane and cell contents with the exception of the nucleus. |
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Definition
| The dynamic internal network of protein fibers that includes microfilaments, intermediate filaments, and microtubules. |
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Term
| density gradient centrifugation |
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Definition
| Procedure in which cellular components are placed in a layer on top of a density gradient, usually made up of a sucrose solution and water. Cell structures migrate during centrifugation, forming a band at the position in the gradient where their own density equals that of the sucrose solution. |
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Term
| differential centrifugation |
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Definition
| Separation of cellular particles according to their mass, size, or density. In differential centrifugation the supernatant is spun at successively higher revolutions per minute. |
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Definition
| A microscope capable of producing high- resolution, highly magnified images through the use of an electron beam (rather than light). Transmission electron microscopes (TEMs) produce images of thin sections; scanning electron microscopes (SEMs) produce images of surfaces. |
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Term
| endoplasmic reticulum (ER) |
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Definition
| An interconnected network of internal membranes in eukaryotic cells enclosing a compartment, the ER lumen. Rough ER has ribosomes attached to the cytosolic surface; smooth ER, a site of lipid biosynthesis, lacks ribosomes. |
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Definition
| The ground substance, fibrous proteins, and other materials between cells of animal tissues (e.g., cartilage). |
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Definition
| A long, whiplike structure extending from certain cells and used in locomotion. (1) Eukaryote flagella are composed of two central single microtubules surrounded by nine double microtubules (9 + 2 structure), all covered by a plasma membrane. (2) Prokaryote flagella are filaments rotated by special structures located in the plasma membrane and cell wall. |
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Definition
| Organelle composed of stacks of flattened, membranous sacs. Mainly responsible for modifying, packaging, and sorting proteins that will be secreted or targeted to other organelles of the internal membrane system or to the plasma membrane; also called Golgi body or Golgi apparatus. |
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Definition
| A stack of thylakoids within a chloroplast. |
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Definition
| Receptor proteins that bind to specific proteins in the extracellular matrix and to membrane proteins on adjacent cells; transmit signals into the cell from the extracellular matrix. |
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Definition
| Intracellular organelles present in many animal cells; contain a variety of hydrolytic enzymes. |
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| (1) In cell biology, the interior of the compartment enclosed by the inner mitochondrial membrane; (2) In zoology, nonliving material secreted by and surrounding connective tissue cells; contains a network of microscopic fibers. |
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| Thin fibers composed of actin protein subunits; form part of the cytoskeleton. |
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Definition
| Hollow cylindrical fibers composed of tubulin protein subunits; major components of the cytoskeleton and found in mitotic spindles, cilia, flagella, centrioles, and basal bodies. |
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Definition
| Minute projections of the plasma membrane that increase the surface area of the cell; found mainly in cells concerned with absorption or secretion, such as those lining the intestine or the kidney tubules. |
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Definition
| Intracellular organelles that are the sites of oxidative phosphorylation in eukaryotes; include an outer membrane and an inner membrane. |
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Definition
| Membrane-bounded organelles in eukaryotic cells containing enzymes that produce or degrade hydrogen peroxide. |
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Definition
| The biological process that captures light energy and transforms it into the chemical energy of organic molecules (e.g., carbohydrates), which are manufactured from carbon dioxide and water; performed by plants, algae, and certain bacteria. |
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Definition
| The selectively permeable surface membrane that encloses the cell contents and through which all materials entering or leaving the cell must pass. |
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Definition
| A family of membrane-bounded organelles occurring in photosynthetic eukaryotic cells; include chloroplasts, chromoplasts, and amyloplasts and other leukoplasts. |
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Definition
| Organelles that are part of the protein synthesis machinery of both prokaryotic and eukaryotic cells; consist of a larger and smaller subunit, each composed of ribosomal RNA (rRNA) and ribosomal proteins. |
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Definition
| A fluid space of the chloroplast, enclosed by the chloroplast inner membrane and surrounding the thylakoids; site of the reactions of the Calvin cycle. |
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Definition
| Small cytoplasmic vesicles that move substances from one membrane system to another. |
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Term
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Definition
| The membrane surrounding a vacuole. |
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Definition
| All forms of transport of a substance across a membrane that do not rely on the potential energy of a concentration gradient for the substance being transported and therefore require an additional energy source (often ATP); includes carrier-mediated active transport, endocytosis, and exocytosis. Compare with diffusion and facilitated diffusion. |
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Definition
| A type of anchoring junction between cells; connects epithelial cells. |
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Term
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Definition
| A molecule containing both hydrophobic and hydrophilic regions. |
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Term
| carrier-mediated active transport |
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Definition
| Transport across a membrane of a substance from a region of low concentration to a region of high concentration; requires both a transport protein with a binding site for the specific substance and an energy source (often ATP). |
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Term
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Definition
| Mechanisms of communication between cells. Cells can signal one another with secreted signaling molecules, or a signaling molecule on one cell can combine with a receptor on another cell. Examples include the synaptic signaling of neurons and endocrine signaling. See signal transduction. |
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Term
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Definition
| A difference in the concentration of a substance from one point to another, as for example, across a cell membrane. |
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Definition
| Button-like plaques, present on two opposing cell surfaces, that hold the cells together by means of protein filaments that span the intercellular space. |
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Definition
| The net movement of particles (atoms, molecules, or ions) from a region of higher concentration to a region of lower concentration (i.e., down a concentration gradient), resulting from random motion. Compare with facilitated diffusion and active transport. |
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Definition
| The active transport of substances into the cell by the formation of invaginated regions of the plasma membrane that pinch off and become cytoplasmic vesicles. Compare with exocytosis. |
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Definition
| A vertebrate red blood cell; contains hemoglobin, which transports oxygen. |
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Definition
| The active transport of materials out of the cell by fusion of cytoplasmic vesicles with the plasma membrane. Compare with endocytosis. |
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Term
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Definition
| The passive transport of ions or molecules by a specific carrier protein in a membrane. As in simple diffusion, net transport is down a concentration gradient, and no additional energy has to be supplied. Compare with diffusion and active transport. |
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Term
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Definition
| The currently accepted model of the plasma membrane and other cell membranes, in which protein molecules float in a phospholipid bilayer. |
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Definition
| Structure consisting of specialized regions of the plasma membrane of two adjacent cells; contains numerous pores that allow the passage of certain small molecules and ions between them. |
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Definition
| The net movement of water (the principal solvent in biological systems) by diffusion through a selectively permeable membrane from a region of higher concentration of water (a hypotonic solution) to a region of lower concentration of water (a hypertonic solution). |
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Term
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Definition
| Cell drinking; a type of endocytosis by which cells engulf and absorb droplets of liquids. |
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Term
| receptor-mediated endocytosis |
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Definition
| A type of endocytosis in which extracellular molecules become bound to specific receptors on the cell surface and then enter the cytoplasm enclosed in vesicles. |
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Term
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Definition
| Active transport system that transports sodium ions out of, and potassium ions into, cells. |
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Term
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Definition
| Specialized structures that form between some animal cells, producing a tight seal that prevents materials from passing through the spaces between the cells. |
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Term
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Definition
| Hydrostatic pressure that develops within a walled cell, such as a plant cell, when the osmotic pressure of the cell's contents is greater than the osmotic pressure of the surrounding fluid. |
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Term
| adenosine triphosphate (ATP) |
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Definition
| An organic compound containing adenine, ribose, and three phosphate groups; of prime importance for energy transfers in cells. |
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Definition
| The aspect of metabolism in which simpler substances are combined to form more complex substances, resulting in the storage of energy, the production of new cellular materials, and growth. Compare with catabolism. |
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Term
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Definition
| The aspect of metabolism in which complex substances are broken down to form simpler substances; catabolic reactions are particularly important in releasing chemical energy stored by the cell. Compare with anabolism. |
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Term
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Definition
| An organic cofactor for an enzyme; generally participates in the reaction by transferring some component, such as electrons or part of a substrate molecule. |
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Term
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Definition
| A substance that binds to the active site of an enzyme, thus lowering the rate of the reaction catalyzed by the enzyme. Compare with noncompetitive inhibitor. |
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Definition
| A nonspontaneous reaction; a reaction requiring a net input of free energy. Compare with exergonic reaction. |
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Definition
| Disorderliness; a quantitative measure of the amount of the random, disordered energy that is unavailable to do work. |
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Term
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Definition
| The temporary association between enzyme and substrate that forms during the course of a catalyzed reaction; also called ES complex. |
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Definition
| A reaction characterized by a release of free energy. Also called spontaneous reaction. Compare with endergonic reaction. |
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Term
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Definition
| A type of enzyme regulation in which the accumulation of the product of a reaction inhibits an earlier reaction in the sequence; also known as end product inhibition. |
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Term
| first law of thermodynamics |
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Definition
| The law of conservation of energy, which states that the total energy of any closed system (any object plus its surroundings, i.e., the universe) remains constant. Compare with second law of thermodynamics. |
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Term
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Definition
| The maximum amount of energy available to do work under the conditions of a biochemical reaction. |
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Term
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Definition
| Oxidized and reduced forms, respectively, of nicotinamide adenine dinucleotide, a coenzyme that transfers electrons (as hydrogen), particularly in catabolic pathways, including cellular respiration |
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Term
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Definition
| A substance that lowers the rate at which an enzyme catalyzes a reaction but does not bind to the active site. Compare with competitive inhibitor. |
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Term
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Definition
| The loss of one or more electrons (or hydrogen atoms) by an atom, ion, or molecule. Compare with reduction. |
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Term
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Definition
| The gain of one or more electrons (or hydrogen atoms) by an atom, ion, or molecule. Compare with oxidation. |
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Term
| second law of thermodynamics |
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Definition
| The physical law that states that the total amount of entropy in the universe continually increases. Compare with first law of thermodynamics. |
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