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Cell Bio MU
Chapter 4
| Question | Answer |
|---|---|
| Membrane Functions pg. 121-122 | 1) Compartmentalize 2) Scaffold for biochemical activities 3) Providing a selectively permeable barrier 4) Transporting solutes 5) Responding to external stimuli 6) Intercellular interaction 7) Energy transduction |
| 5) of "Membrane Functions" | ~Single transduction: the response of a cell to external stimuli ~Receptors: combine with specific molecules (ligands) or respond to other types of stimuli such as light or mechanical tension |
| Lipid bilayer pg. 123 | A bimolecular layer of lipids |
| Fluid Mosaic Model pg. 124 | (the "central dogma" of membrane biology for more that thee decades); the lipid bilayer remains the core of the core of the membrane, but attention is focused on the physical state of the lipid |
| Amphipathic pg. 125 | contains both hydrophilic and hydrophobic regions |
| Phospholipids pg. 125 | Most membrane lipids contain a phosphate group, made of phospholipids |
| Phosphoglycerides pg. 125 | Membrane phospholipids that are built on a glycerol backbone |
| Diglycerides pg. 125 | Membrane glycerides are diglycerides--only two of the hydroxyl groups of the glycerol are esterified to fatty acids, the third is esterified to a hydrophilic phosphate group |
| Head group pg. 126 | A highly water-soluble domain at one end of the molecule (PC, PE, or PI); each of those (PC, PE, or PI) are small and hydrophilic and, together with the negatively charged phosphate to which it is attached, forms the head group |
| Sphingolipids pg. 126 | Derivatives of sphingosine, an amino alcohol that contains a long hydrocarbon chain; consist of sphingosine linked to a fatty acid by its amino group; ceramide |
| Glycolipid pg. 126 | If the substitution on a ? is a carbohydrate, the molecule is a glycolipid |
| Cholesterol pg. 127 | A lipid component of certain membranes; in certain animal cells may constitute up to 50% of the lipid molecules in the plasma membrane |
| Glycosylation pg. 129 | The modification of proteins was discussed in briefly on pg. 54. The addition of carbohydrate, or glycosylation, is the most complex of these modifications. |
| Oligosaccharides pg. 129 | the carbohydrate of glycoproteins; short, branched hydrophilic; typically having fewer than about 15 sugars per chain |
| 1st ... of Three distinct classes of membrane proteins: distinguished by the intimacy of their relationship to the lipid bilayer pg. 130 | 1) Integral proteins: penetrate the lipid bilayer; transmembrane proteins - they pass e149ntirely through the lipid bilayer and thus have domains that protrude from both the extracellular and cytoplasmic sides of the membrane. |
| 2nd .... | Peripheral proteins: located entirely outside of the lipid bilayer, on either the cytoplasmic or extracellular side, yet are associated with the surface of the membrane by noncovalent bonds. |
| 3rd .... | Lipid-anchored proteins: located outside the lipid bilayer, on either the extracellular or cytoplasmic surface, but are covalently linked to a lipid molecule that is situated within the bilayer. |
| Freeze-Fracture replication pg. 132 | Procedure responsible for the concept that proteins penetrate through membranes, rather than simply remaining external to the bilayer; tissue is frozen solid and then struck with a knife blade, which fractures the block into two pieces. |
| Transmembrane domains pg. 134 | Segments of a protein embedded within the membrane; have a simple structure; consist of a string of about 20 predominantly nonpolar amino acids that span the core of the lipid bilayer as an (alpha symbol)helix |
| GPI-anchored proteins pg. 137 | Peripheral membrane proteins containing this type (refer to next block) of glycosyl-phosphatidylinositol linkage |
| cont... | (numerous proteins present on the external face of the plasma membrane are bound to the membrane by a small, complex oligosaccharide linked to a molecule of phosphatidylinositol that is embedded int he outer leaflet of the lipid bilayer) |
| Transition Temperature pg. 138 | A lipid is converted from a liquid crystalline phase to a frozen crystalline gel in which the movement of the phospholipid fatty acid chains is greatly restricted; this change in temp is called transition temperature |
| Lipid rafts pg. 13 | Microdomains (Patches of cholesterol and sphingolipid) that tend to float within the more fluid and disordered environment of the artificial bilayer due to their distinctive physical properties |
| Cell fusion pg. 141 | A technique whereby two different types of cells, or cells from two different species, can be fused to produce one cell with a common cytoplasm and a single, continuous plasma membrane |
| Fluorescence recovery after photobleaching (FRAP) pg. 142 | Allowed researchers to follow the movements of molecules in the membranes of living cells using the light microscope; can only follow the average movement of a relatively large number of labeled molecules as they diffuse over a relatively large distance |
| Single-particle tracking (SPT) pg. 142 | Individual membrane protein molecules are labeled, usually with antibody-coated gold particles (approx. 40 nm in diameter), and the movements of the labeled molecules are followed by computer enhanced video microscopy. |
| Diffusion pg. 147 | A spontaneous process in which a substance moves from a region of high concentration to a region of low concentration, eventually eliminating the concentration diff between the two regions. |
| Electrochemical gradient pg. 148 | A gradient of electrochemical potential, usually for an ion that can move across a membrane. The gradient consists of two parts, the electrical potential and a difference in the chemical concentration across a membrane |
| Partition coefficient pg. 149 | One simple measure of the polarity (or nonpolarity) of a substance, which is the ratio of its solubility in a nonpolar solvent, such as octanol or a vegetable oil, to that in water under conditions where the nonpolar solvent and water are mixed together |
| Semipermeable pg. 149 | Water molecules move much more rapidly through a cell membrane that do dissolved ions or small polar organic solutes, which are essentially nonpenetrating; this difference in the penetrability of water vs solutes, means membranes are semipermeable |
| Osmosis pg. 149 | Water moves readily through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration |
| Hypertonic (or hypoosmotic) pg. 149 | When two compartments of different solute concentration are separated by a semipermeable membrane, the compartment of higher solute concentration is called hypertonic; when a cell is placed in hypertonic sol'n it loses water by osmosis and shrinks |
| Hypotonic (or hypoosmotic) pg. 149 | " " ; the compartment of lower solute concentration; when a cell is placed in a hypotonic sol'n, it gains water by osmosis and swells |
| Isotonic (or isosmotic) pg. 150 | When the internal solute concentration (which includes a high concentration of dissolved proteins) equals the external solute concentration; both the internal and external fluids are isotonic; no net movement of water into or out of the cells occurs |
| Plasmolysis pg. 150 | The process of if a plant cell is placed into a hypertonic medium, its volume shrinks as the plasma membrane pulls away from the surrounding cell wall; the loss of water due to plasmolysis causes plants to lose their support and wilt |
| Conductance pg. 151 | The rapid movement of ions across membranes |
| Ion channels pg. 151 | Cell membranes contain ion channels; openings in the membrane that are permeable to specific ions |
| Gated pg. 152 | Most of the ion channels that have been identified can exist in either an open or a closed conformation; such channels are gated; subject to complex physiologic regulation and can be induced by a variety of factors depending on the particular channel |
| 1st of Three major categories of gated channels pg. 152 | 1) Voltage-gated channels: whose conformational sate depends on the diff in ionic charge on the two sides of the membrane |
| 2nd ... | 2) Ligand-gated channels: whose conformational state depends on the binding of a specific molecule (the ligand), which is usually not the solute that passes through the channel |
| 3rd ... | Mechano-gated channels: whose conformation state depends on mechanical forces (e.g. stretch tension) that are applied to the membrane |
| 1st ... These six helices (Eukaryotic Kv channel subunits containing 6 membrane-assoc. helices, named S1-S6) can be grouped into two functionally distinct domains | Pore domain: has the same basic architecture as that of the entire bacterial channel and contains the selectivity filter that permits the selective passage of K+ ions |
| 2nd ... | Voltage-sensing domain: consists of helices S1-S4 that senses the voltage across the plasma membrane |
| Facilitative transporter pg. 156 | Facilitates the diffusion process; the diffusion substance first binds selectively to a membrane-spanning protein (facilitative transporter) |
| Facilitated diffusion pg. 156 | Similar in many ways to an enzyme-catalyzed reaction; like enzymes, facilitative transporters are specific for the molecules they transport, discriminating, for example, btw D and L stereoisomers |
| Active transport | The ability of a cell to generate such steep concentration gradients across its plasma membrane cannot occur buy either simple or facilitated diffusion. Rather, these gradients must be generated by active transport |
| Cotransport pg. 160 | The movement of glucose across the apical plasma membrane of the epithelial cells, against a concentration gradient, occurs by cotransport with sodium ions |
| Antiport pg. 161 | Numerous cotransporters have been isolated that engage in antiport, in which the two transported species move in opposite directions |
| Dendrites pg. 164 | Fine extensions that extend from the cell bodies of most neurons; receive incoming information from external sources, typically other neurons |
| Axon pg. 164 | Extend from the cell body in a single, more prominent extension (than that of the dendrites) which conduct outgoing impulses away from the cell body and toward the target cell(s) |
| Myelin sheath pg. 163 | Comprises individual Schwann cells that have wrapped themselves around the axon; the sites where the axon lacks myelin wrapping are called nodes of Ranvier |
| Membrane potential pg. 165 | Not unique to nerve cells; such potentials are present in all types of cells, the magnitude varying btw about -15 and -100mV |
| Resting potential pg. 165 | When a nerve cell or muscle cell is in an unexcited state, the membrane potential is referred to as the resting potential because it is subject to dramatic change |
| Depolarization pg. 166 | Because the positive change in membrane voltage causes a decrease in the polarity between the two sides of the membrane, it is called depolarization |
| Threshold pg. 166 | When the stimulus depolarizes the membrane beyond a certain point, called threshold, which occurs at about -50 mV |
| Nerve impulse pg. 167 | Once an action potential has been initiated, it does not remain localized at a particular site but is propagated as a nerve impulse down the length of the cell to the nerve terminals |
| Saltatory conduction pg. 167 | Propagation of an impulse by a certain mechanism |
| Synapses pg. 168 | Specialized junctions where neurons are linked with their target cells |
| Synaptic cleft pg. 168 | The gap between two cells; the cells do not make direct contact by are separated from each other by a narrow gap of about 20 to 50 nm |
| Presynaptic cell pg. 168 | (a receptor cell or a neuron); conducts impulses toward a synapse |
| Postsynaptic cell pg. 169 | (a neuron, muscle, or gland cell); always lies on the receiving side of a synapse |
| Neuromuscular junctions pg. 169 | A number of synapses btw the terminal branches of an axon and a skeletal muscle cell- synapses of this type are called neuromuscular junctions |
| Synaptic vesicles pg. 169 | Serve as storage sites for the chemical transmitters that on postsynaptic cells; the very tips (terminal knobs) of the branches of an axon appear in the electron microscope to contain large numbers of synaptic vesicles |
| Neurotransmitters pg. 169 | Two of the best studied neurotransmitters are acetylcholine and norepinephrine; transmit impulses to the body's skeletal and cardiac muscles |
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Briawna
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