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Cell Bio-214 Exam 2
| Question | Answer |
|---|---|
| Compartmentalization | membranes form continuous sheets that enclose intracellular compartments |
| Scaffold for Biochemical Activities | membranes provide a framework that organizes enzymes for effective interaction |
| Selectively permeable barrier | membranes allow regulated exchange of substances between compartments |
| transporting solutes | membrane proteins facilitate the movement of substances between compartments |
| responding to external signals | membrane receptors transduce signals from outside the cell in response to specific ligand |
| Intracellular interaction | membranes mediate recognition and interaction between adjacent cells en |
| Energy transduction | membranes transduce photosynthetic energy, convert chemical energy to ATP, and store energy |
| Functions of Membrane (7) | Compartmentalization; Scaffold for biochemical activities; selectively permeable barrier; transporting solutes; responding to external signals; intracellular interaction; energy transduction |
| Membrane composition | the lipid and protein components are bound together by non-covalent bonds; membranes also contain carbohydrates |
| Amphipathic | The membrane has both non-polar and polar aspects |
| Three main types of membrane lipids | Phosphoglyerides; Sphingolipids; Cholesterol |
| Phosphoglycerides | diacylglycerides with small functional head groups linked to the glycerol backbone by phosphate ester bonds |
| Sphingolipids | are ceramides formed by the attachment of sphingosine to fatty acids |
| Cholesterol | smaller and less amphipathic lipid that is only found in animals |
| Glycoproteins | have short, branched carbohydrates for interactions with other cells and structures outside the cell |
| Glycolipids | have larger carbohydrate chains that may be cell-to-cell recognition sites |
| Integral Membrane Proteins | are amphiphatic with hydrophobic domains anchoring them in the bilayer and hydrophilic regions forming functional domains outside of the bilayer |
| Peripheral proteins | attached to the membrane by weak bonds and are easily solubilized |
| Gluycophosphatidylinositol(GPI)-linked proteins | found on the outer leaflet can be released by inositol-specific phospholipases |
| Unsaturated fatty acids ____ the temperature at which the liquid-crystal/gell phase transition occurs | lowers |
| Membrane fluidity | makes it possible for proteins to move in the membrane and for membranes to assemble and grow |
| How to organisms maintain membrane fluidity as temperatures change? | By altering the composition of membrane lipids |
| Phospholipases/ Acyltransferases | help saturate or desaturate of acyl chains and replacement of acyl chains |
| Lipid rafts | cholesterol and sphingolipids tend to pack together to form highly ordered microdomains forming lipid rafts that float within the more fluid and disordered environment |
| Provide a favorable environment for cell-surface receptors and GPI-anchored proteins | Lipid rafts |
| Net flux | the difference between influx and efflux of materials |
| Diffusion | spontaneous movement of material from a region of high concentration to a region of low concentration |
| The free-energy change during diffusion of nonelectrolytes depends on the _____________ | concentration gradient |
| The free-energy change during diffusion of electrolytes depends on the _______________ | electrochemical gradient |
| Osmosis | diffusion of water through a semipermeable membrane |
| Cells swell in a __________ solution | hypotonic |
| Cells shrink in a _________ solution | hypertonic |
| Cells remain unchanged in a ______ solution | isotonic |
| Plant cells develop _______ in hypotonic solutions because cell walls prevent swelling | turgor |
| Plasmolysis | when plant cells are placed in a hypertonic solution |
| Aquaporins | specialized protein channels that allow the passive movement of water |
| Facilitated Diffusion | transport that occurs by using a facilitative transporter to move large or hydrophilic substances |
| _____ stimulates glucose uptake by causing the insertion into the cell membrane of vesicles containing preformed glucose transporters | Insulin |
| Active transport | maintains the gradients for potassium, sodium, calcium, and other ions across the cell membrane; it is coupled with ATP hydrolysis |
| Na+/K+ ATPase | requires K+ outside, Na+ inside, and is inhibited by ouabain |
| The ratio of Na+/K+ | 3:2 |
| ATPase | P-type pump, in which phosphorylation causes changes in conformation and ion affinity that allow transport against gradients |
| Endomembrane system | endoplasmic reticulum, Golgi complex, endosomes, lysosomes, and vacuoles functioning as part of a coordinated unit |
| transport vesicles | shuttle materials between organelles |
| Biosynthetic pathways | synthesis, modification and transport of proteins |
| Secretory pathways | when proteins are discharged from the cell |
| Constitutive secretion | secretions continue in a continuous fashion |
| Regulated secretion | respond to a stimulus |
| Secretory granules | where materials to be secreted are stored; large and membrane-bound |
| Smooth ER | synthesis of steroid hormones; detoxification in the liver; sequestration of calcium ions in muscle |
| Rough ER | starting point of the biosynthetic pathway; transports protein |
| Golgi complex | stack of flattened cisternae; cis face towards ER, trans face towards opposite side |
| cis Golgi network (CGN) | functions to sort proteins for the ER or the next Golgi station |
| trans Golgi network | functions in sorting proteins either to the cell membrane or various intracellular destinations |
| Glycosylation | assembly of carbohydrates found in glycolipids and glycoproteins takes place in the Golgi |
| glycosyltransferases | sequence of incorporation of sugars into oligosaccharides |
| cisternal maturation model | each cistern matures as it moves from the cis face to the trans face |
| Vesicular transport model | cargo is shuttled from the CGN to the TGN in vesicles |
| A current model | similar to cisternal maturation model but with backward transport in vesicles |
| coated vesicles | carry materials between compartments |
| two distinct functions of protein coats | cause the membrane to curve and form a vesicle; select the components to be carried by vesicle |
| COPII-coated vesicles | move materials from the ER "forward" to the ERGIC and Golgi complex |
| COPI-coated vesicles | move materials from ERGIC and Golgi backward to the ER or from the trans Golgi to the cis Golgi cisternae |
| Clathrin-coated vesicles | move materials from the TGN to endosomes, lysosomes, and plant vacuoles |
| Exocytosis | discharge of a secretory vesicle or granule after fusion with plasma membrane |
| Exocytosis is triggered by an increase in ______ | Ca2+ |
| fusion pore | form when the vesicle and plasma membrane come into contact |
| lysosomes contain ____________ which can digest every type of biological molecule | acid hydrolases |
| The low pH optimum for lysosomes is maintained by ___________ | a proton pump (H+ - ATPase) |
| Autophagy | an organelle is surrounded by a double membrane and a structure called an autophagosome is produced |
| Autophagolysosome | produced when the autophagosome is then fuse with a lysosome |
| Lysosomal storage disorders | results from the absence of specific lysosomal enzymes thus allowing undigested material to accumulate |
| Tay-Sachs disease | results from a deficiency in an enzyme responsible for degrading gangliosides, which is a major component of cell membranes |
| Endocytosis | uptake of cell surface receptors and bound extracellular ligands |
| phagocytosis | uptake of particulate matter |
| Pinocytosis | nonspecific uptake of extracellular fluids |
| Receptor-mediated endocytosis (RME) | uptake of specific extracellular ligands following their binding to receptors |
| Substances that enter the cell through RME become bound to ___________ on the plasma membrane | coated pits |
| ________ are located near the periphery of the cell. It sorts materials and sends bound ligands to the ______________ | early endosomes; late endosomes |
| Another name for late endosomes | multivesicular bodies(MVBs) |
| Extracellular messenger molecules | transmit messages between cells |
| Autocrine signaling | the cell has receptors on its surface that respond to the messenger |
| Paracrine signaling | messenger molecules travel short distances through extracellular space |
| Endocrine signaling | messenger molecules reach their target cells through the bloodstream |
| Some cell surface receptors generate an intracellular ____________ through an enzyme called an ________ | second messengers; effector |
| Target proteins | ultimately receive a message to alter cell activity |
| Extracellular messengers (5) | small molecules; NO and CO; Steroids; Eicosanoids; peptides and proteins |
| Eicosanoids | lipids derived from fatty acids |
| Receptor types (5) | GPCRs; RTKs; ligand-gated channels; steroid hormone receptors; specialized receptors (B- and T- cell receptors) |
| GPCRs have ______ transmembrane domains and interact with G proteins | seven |
| GPCR signaling involves (4) | Ligand; GPCR; heterotrimeric G protein; Effector protein |
| _____ is exchanged for ____ on the G protein, activating the G protein | GDP; GTP |
| Desensitization | blocking active receptors from turning on additional G proteins |
| G protein-coupled receptor kinase (GRK) | phosphorylates a GPCR |
| Arrestins | compete with G proteins to bind GPCRs |
| Phosphorylation of GPCRs by GRKs promotes _________ | arrestin binding |
| Cyclic AMP | a second messenger that is released into the cytoplasm after binding of a ligand |
| Second messengers | amplify the response to a single extracellular ligand |
| Phosphatidylinositides (PI) | second messengers derived form phosphatodylinositol |
| Phosphatidylinositol-specific phospholipase C-beta | produces second messengers derived from phosphatidylinositol-inositol triphosphate (IP3) and diacylglycerol (DAG) |
| DAG | activates protein kinase C which phosphorylates serine and threonine residues on target proteins |
| PH domains | lipid-binding domains form from phosphorylated phosphoinositides |
| Binding of IP3 | opens the calcium channel located at the surface of the SER and allows Ca2+ ions to diffuse out |
| Different stimuli acting on the same target cell may induce the ____ response | same |
| _______ and ______ are hormones that induce glucose breakdown and inhibit its synthesis | Glucagon; epinephrine |
| adenylyl cyclase | synthesizes cAMP |
| protein kinase A | cAMP molecules diffuse into the cytoplasm and bind to this enzyme to cause glucose mobilization |
| ________ halt the reaction casade | phosphatases |
| Rhodopsin | a photosensitive protein for black-and-white vision that is also a GPCR |
| Retinitis pigmentosa | progressive degeneration of the retina, can be caused by mutation in rhodopsin's ability to activate a G protein |
| Protein-tyrosine kinases | regulate cell growth, division, differentiation, survival, and migration |
| Receptor protein-tyrosine kinases (RTKs) | are cell surface receptors of the protein-tyrosine kinase family which are responsible in phosphorylating tyrosine residues on target proteins |
| Two consequences of RTK phosphoryation | increases receptor kinase activity; provides binding sites for other signaling proteins in the pathway |
| Phosphorylated tyrosine bind effector proteins that have ________ and _______ | SH2 domains; PTB domains |
| SH2 and PTB domain proteins include(4) | adaptor proteins that bind to other proteins; docking proteins that supply receptors with other tyrosine phosphorylation sites; signaling enzymes; transcription factors |
| Ras | is a monomeric G protein embedded in the membrane by a lipid group and is activated when bound to GTP and inactive when bound to GDP |
| GTPase-activiating proteins (GAPs) | shorten the active time of Ras |
| Guanine nucleotide-exchange factors (GEFs) | stimulate the exchange of GDP for GTP |
| Guanine nucleotide-dissociation inhibitors (GDIs) | inhibit the release of GDP |
| Ras-MAP kinase cascade | a cascade of enzymes resulting in activation of transcription factors |
| Insulin | regulates blood glucose levels by increasing cellular uptake of glucose |
| Insulin receptor is this type of receptor | protein-tyrosine kinase |
| insulin receptor substrate proteins (IRSs) | bind proteins with SH2 domains which activate downstream signal molecules |
| PI-3 kinase (PI3K) | SH2 domains-containing proteins are kinases that phosphorylate a lipid |
| Protein Kinase B (PKB) | regulates glucose uptake by GLUT4 transporters |
| Diabetes mellitus | caused by defects in insulin signaling |
| Type 2 diabetes | caused by gradual insensitivity to insulin |
| Calcium binds to calcium-binding proteins such as _______ which affects other proteins | calmodulin |
| Signals form unrelated receptors can _____ to activate a common effector | converge |
| Identical signals can _____ to activate a variety of effectors | diverge |
| signals can be passed back and forth between pathways as a result of _____ | crosstalk |
| Convergence | GPCRs, receptor tyrosin kinases, and integrins bind to different ligans but they all can lead to a docking site for Gbr2 |
| Divergence | a single stimulus sends signals along a variety of different pathways |
| Crosstalk examples (2) | cAMP can block signals transmitted through the MAP kinase cascade; Ca2+ and cAMP can influence each other's pathways |
| nitric oxide synthase | produces NO |
| NO stimulates ________ to form cGMP | guanylyl cyclase |
| CGMP | decreases cytosolic calcium and relaxes smooth muscle |
| Apoptosis | is an ordered process for programmed cell death |
| Capases | activate apoptotic changes |
| Capases target (4) | protein kinases; lamins' proteins of the cytoskeleton; caspase activated DNase (CAD) |
| Extrinsic Pathway of Apoptosis (4 steps) | Tumor necrosis factor (TNF) is detected by TNF cell receptors; bound TNF receptors activate procaspases; procaspases are converted into caspases; caspases activate executioner caspases leading to apoptosis |
| Intrinsic Patway of Apoptosis (2 steps) | Proapoptotic proteins stimulate mitochondria to leak proteins, mostly cytochrome C; Release of apoptotic mitochondrial proteins irreversibly commits the cell to apoptosis |
| Apoptotic cells are cleared by _______ | phagocytosis |
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