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Chapter 3: The Cell - Vocabulary actin filaments Muscular protein filament in sarcomeres; its movement shortens sarcomeres, yielding muscle contraction. Actin filaments play role in movement of cell + organelles. amphipathic Molecule that has both positive and negative pole. apoptosis Programmed cell death involving cascade of specific cellular events leading to death + destruction of cell. aquaporins Channel proteins through which water can diffuse across membranes. autocrine signals Diffuse from one part of cell to another part of same cell. autophagy Process by which cell continually renews itself by breaking down + recycling cell parts. blood Fluid circulated by heart through closed system of vessels. bulk flow Overall movement of fluid in one direction in organism. carriers Carry particles across membrane by active transport. catalase Enzyme produced in all cells that decomposes hydrogen peroxide (H2O2), a by-product of cell respiration. cells Smallest units that display properties of life; composed of organelle-containing cytoplasm surrounded by plasma membrane. cell membrane receptors Span entire thickness of membrane; therefore, they are in contact w/ both extracellular environment + cytoplasm. cellulose Polysaccharide that is major complex carbohydrate in plant cell walls. cell walls Structures that surround plant, protistan, fungal, or bacterial cell + maintain cell’s shape + rigidity. centrioles Cell organelles, existing in pairs, that occur in centrosome + may help organize mitotic spindle for chromosome movement during animal cell division. centrosomes Central microtubule organizing centers of cells. In animal cells, it contains two centrioles. Chapter 3: The Cell - Vocabulary chitin Strong, but flexible, nitrogenous polysaccharide found in exoskeleton of arthropods and in cell walls of fungi. cholesterol molecules Embedded in interior of phospholipid bilayer in order to stabilize membrane. chromatin network Network of DNA strands + associated proteins observed within nucleus that is not dividing. cilia Short, hair-like projections from plasma membrane, occurring usually in larger numbers. cleavage furrows Shallow grooves in cell surface in animal cell where cytokinesis is taking place. coated vesicles Receptors carrying ligands that migrated + clustered along membrane + turned inwards. contractile vacuoles Found in many freshwater protists; used to pump out excess water. countercurrent exchange Fluids flow side-by-side in opposite directions, as in exchange of fluid in kidneys cristae Short, finger-like projections formed by folding of inner membrane of mitochondria. cyclic AMP (cAMP) ATP-related compound that acts as second messenger in peptide hormone transduction; it initiates activity of metabolic machinery. cytoplasmic streaming Involvement of cytoskeleton with flow of cytoplasm. desmosomes Intracellular junctions that connect cytoskeletons of adjacent cells. diffusion Movement of molecules or ions from region of higher to lower concentration; it requires no energy and tends to lead to equal distribution. electron transport chain (ETC) Passage of electrons along series of membrane-bound electron carriers from higher to lower energy level; energy released is used for synthesis of ATP. endocrine signals Hormones; travel anywhere in blood to reach target cells. estrogen Female sex hormone that helps maintain sexual organs and secondary sex characteristics; example of hydrophobic chemical messenger. Chapter 3: The Cell - Vocabulary eukaryotic cells Type of cell that has membrane-bounded nucleus + membranous organelles; found in organisms within domain Eukarya. exocytosis Process in which intracellular vesicle fuses w/ plasma membrane so that vesicle’s contents are released outside cell. facilitated diffusion Diffusion that involves protein channels. first messenger Chemical signal such as peptide hormone that binds to plasma membrane receptor protein + alters metabolism of cell b/c second messenger is activated. flagella Long, slender extension used for locomotion by some bacteria, protozoans, and sperm. fluid mosaic model Model for plasma membrane based on changing location + pattern of protein molecules in fluid phospholipid bilayer. food vacuoles Formed by phagocytosis of foreign material. G-protein-coupled receptors Example of cell surface receptors. gap junctions Junction between cells formed by joining of 2 adjacent plasma membranes; it lends strength + allows ions, sugars, & small molecules to pass between cells. gated channels Open + close in response to variables such as turgor pressure of cell. Golgi apparatus Organelle consisting of sacs + vesicles that process, package, & distribute molecules about or from cell. heart Muscular organ whose contraction causes blood to circulate in body of animal. hydrolytic enzymes Digestive enzymes; found in lysosomes. hydrophilic protein channels Required by facilitated diffusion; passively transports specific substances across plasma membrane. hydrophilic signalling molecules Cannot diffuse through membrane; however, they can bind to part of receptor on cell surface that changes shape on cytoplasmic side of same receptor. hypertonic Higher solute concentration than cytoplasm of cell; causes cell to lose water by osmosis. hypotonic Lower solute concentration than cytoplasm of cell; causes cell to gain water by osmosis. Chapter 3: The Cell - Vocabulary integral proteins Proteins embedded in plasma membrane; have nonpolar regions that completely span hydrophobic interior of membrane. intracellular digestion Digestion that occurs within cell. ion channel receptors Example of cell surface receptors. isotonic Solution that is equal in solute concentration to that of cytoplasm of cell; causes cell to neither gain nor lose water by osmosis. ligands Molecules that bind specifically to receptor site of another molecule. ligand receptor complex Either immediately activates pathway in cytoplasm or migrates to nucleus, where it acts as transcription factor + switches genes on/off. lysosomes Membrane-bounded vesicle that contains hydrolytic enzymes for digesting macromolecules. microfilaments Assembled from actin filaments; help support shape of cell. microtubules Small, cylindrical organelles composed of tubulin protein around empty central core; present in cytoplasm, centrioles, cilia, and flagella. microtubule organizing centers (MTOCs) Non-membranous structures that lie outside nuclear membrane; organize spindle fibers + give rise to spindle apparatus during cell division. middle lamella Formed when plant cell divides; thin, gluey layer formed between two new plant cells. nitrous oxide (NO) Example of hydrophobic chemical messenger. nuclear envelopes Double membranes that surround nucleus in eukaryotic cells + is connected to endoplasmic reticulum; have pores that allow substances to pass between nucleus and cytoplasm. osmosis Diffusion of water through differentially permeable membrane. osmotic potential Tendency of water to move across permeable membrane into solution. paracrine signals Send messages to nearby cells by diffusion. Chapter 3: The Cell - Vocabulary passive transport Movement of molecules down concentration gradient from region of high concentration to region of low concentration until equilibrium is reached; examples include diffusion + osmosis. peripheral proteins Proteins that occur on cytoplasmic side of plasma membrane; loosely bound to surface of membrane. peroxisomes Enzyme-filled vesicle in which fatty acids + amino acids are metabolized to hydrogen peroxide (H2O2) that is broken down to harmless products. phagocytosis Process by which amoeboid-type cells engulf large substances, forming intracellular vacuole. phospholipid bilayer Describes plasma membrane structure: 2 layers of phospholipids; hydrophobic tails face inwards, while hydrophilic heads face outwards. pinocytosis Process by which vesicle formation brings macromolecules into the cell. plasma membranes Membranes surrounding the cytoplasm that consist of phospholipid bilayer w/ embedded proteins; function to regulate entrance/exit of molecules from cell. plasmodesmata In plants, cytoplasmic strands that extend through pores + in cell wall + connect the cytoplasm of two adjacent cells. plasmolysis Contraction of cell contents due to loss of water. pores Allows for transport of molecules, such as mRNA, that are too large to diffuse directly through nuclear envelope. primary cell walls Cell walls that are located immediately outside plasma membrane. protein kinase receptors Example of cell surface receptors. pseudopods Cytoplasmic extension of amoeboid protists; used for locomotion + engulfing food. pumps Carry particles across membrane via active transport. quorum sensing Phenomenon that allows simple bacterial cells to secrete molecules that enable them to respond to changes in their population density. receptors Type of membrane protein that binds to specific molecules in environment, providing mechanism for cell to sense + adjust to its surroundings. Chapter 3: The Cell - Vocabulary receptor-mediated endocytosis Selective uptake of molecules into cell by vacuole formation after they bind to specific receptor proteins in plasma membrane. rough endoplasmic reticulum Membranous system of tubules, vesicles, & sacs in cells; has attached ribosomes. secondary cell walls Produced by some cells; secondary cell walls located underneath primary cell walls. second messenger Chemical signal such as cyclic AMP that causes cell to respond to the first messenger—hormone bound to plasma membrane receptor protein. secrete To release substance by exocytosis from cell that may be gland or part of gland. selectively permeable Describes plasma membrane; only certain molecules are allowed to pass through. signal transduction pathway Coordinates activities within, between, and among individual cells; supports entire organism. simple diffusion Diffusion that does not involve protein channels. sodium-potassium pump Carrier protein in plasma membrane that moves sodium ions out of + potassium ions into animal cells; important in nerve + muscle cells. solute Substance dissolved in solvent, forming solution. solvent Liquid portion of solution; serves to dissolve solute. spindle fibers Help separate chromosomes during mitosis + meiosis; consist of microtubules organized into 9 triplets w/ no microtubules in center. steroid hormones Type of hormone that has same complex of four carbon rings, but each one has different side chains. synaptic signalling Occurs in animal nervous system; neurotransmitters are signalling molecules. testosterone Male sex hormone that helps maintain sexual organs and secondary sex characteristics; example of hydrophobic chemical messenger. theory of endosymbiosis States that eukaryotic cells emerged when mitochondria + chloroplasts, once free-living prokaryotes, took up permanent residence inside other larger cells, about 1.5 billion years ago. Chapter 3: The Cell - Vocabulary thylakoids Flattened sacs within granum whose membranes contain chlorophyll + where light reactions of photosynthesis occur. thyroid hormones Example of hydrophobic chemical messenger. tight junctions Junction between cells when adjacent plasma membrane proteins join to form impermeable barrier. transcription factors In eukaryotes, proteins required for initiation of transcription by RNA polymerase. turgid Another word for “swollen”. turgor pressure Pressure of cell contents against cell wall; in plant cells, determined by water content of the vacuole + provides internal support. urinary bladder Organ where urine is stored. water potential Potential energy of water; measure of capability to release/take up water relative to another substance.