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receptor
Molecule or structure that responds to a specific form of stimulation.
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hydrogen bond
Attraction that forms between a covalently bonded hydrogen atom and another atom taking part in a separate covalent bond.
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cohesion
Tendency of molecules to stick together.
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ATP
Nucleotide that consists of an adenine base, five carbon ribose sugar, and three phosphate groups. Also functions as an energy carrier.
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nucleotide
Monomer of nucleic acids; has five-carbon sugar, nitrogen-containing base, and phosphate groups.
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amino acid
Small organic compound with a carboxyl group, an amine group, and a characteristic side group (R).
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phospholipid
A lipid with a phosphate group in its hydrophilic head, and two nonpolar fatty acid tails.
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fatty acid
Organic compound that consists of a long chain of carbon atoms with an acidic carboxyl group at one end.
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nucleoid
Region of cytoplasm where the DNA is concentrated inside a prokaryotic cell.
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surface-to-volume ratio
A relationship in which the volume of an object increases with the cube of the diameter, but the surface area increases with the square.
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adhesion protein
Membrane protein that helps cells stick together in tissues.
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receptor protein
Plasma membrane protein that binds to a particular substance outside of the cell.
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transport protein
Protein that passively or actively assists specific ions or molecules across a membrane.
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endomembrane system
Series of interacting organelles (endoplasmic reticulum, Golgi bodies, vesicles) between nucleus and plasma membrane; produces lipids, proteins.
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endoplasmic reticulum (ER)
Organelle that is a continuous system of sacs and tubes; extension of the nuclear envelope. Rough ER is studded with ribosomes; smooth ER is not.
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peroxisome
Enzyme-filled vesicle that breaks down amino acids, fatty acids, and toxic substances.
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vesicle
Small, membrane-enclosed, saclike organelle; different kinds store, transport, or degrade their contents.
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cytoskeleton
Dynamic framework of protein fi laments that support, organize, and move eukaryotic cells and their internal structures.
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intermediate filament
Cytoskeletal element that locks cells and tissues together.
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microfilament
Reinforcing cytoskeletal element; fiber of actin subunits.
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microtubule
Cytoskeletal element involved in movement; hollow filament of tubulin subunits.
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motor protein
Type of energy-using protein that interacts with cytoskeletal elements to move the cells parts or the whole cell.
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pseudopod
Extendable lobe of membrane-enclosed cytoplasm.
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adhering junction
Cell junction that anchors cells to each other or to extracellular matrix.
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cell junction
Structure that connects a cell to another cell or to extracellular matrix.
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extracellular matrix (ECM) Complex mixture of substances secreted by cells; supports cells and tissues; roles in cell signaling.
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Gap junction
Cell junction that forms a channel across the plasma membranes of adjoining animal cells.
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tight junctions
- Arrays of fibrous proteins; join epithelial cells and collectively prevent fluids from leaking between them.
- first law of thermodynamics
- Energy cannot be created or destroyed.
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second law of thermodynamics
Energy tends to disperse.
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phosphorylation
Phosphate-group transfer.
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product
A molecule remaining at the end of a reaction.
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active site
Pocket in an enzyme where substrates bind and a reaction occurs.
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allosteric
Describes a region of an enzyme other than the active site that can bind regulatory molecules.
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coenzyme
An organic molecule that is a cofactor.
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cofactor
A metal ion or a coenzyme that associates with an enzyme and is necessary for its function.
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enzyme
Protein or RNA that speeds a reaction without being changed by it.
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metabolic pathway
Series of enzyme-mediated reactions by which cells build, remodel, or break down an organic molecule.
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concentration
The number of molecules or ions per unit volume of a fluid.
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concentration gradient
Difference in concentration between adjoining regions of fluid.
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electron transfer chain
Array of enzymes and other molecules that accept and give up electrons in sequence, thus releasing the energy of the electrons in usable increments.
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osmosis
The diffusion of water across a selectively permeable membrane.
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osmotic pressure
Amount of turgor that prevents osmosis into cytoplasm or other hypertonic fluid.
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active transport
Energy-requiring mechanism by which a transport protein pumps a solute across a cell membrane against its concentration gradient.
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passive transport
Mechanism by which a concentration gradient drives the movement of a solute across a cell membrane through a transport protein. Requires no energy input.
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