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UCSD BILD 1 - Ribosomes

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Ribosomes: Protein Factoriesin the Cell• Ribosomes are particles made of ribosomalRNA and protein• Ribosomes carry out protein synthesis in twolocations:– In the cytosol (free ribosomes)– On the outside of the endoplasmic reticulum(ER) or the nuclear envelope (boundribosomes)LE 6-11Ribosomes0.5 µmERCytosolEndoplasmicreticulum (ER)Free ribosomesBound ribosomesLargesubunitSmallsubunitDiagram ofa ribosomeTEM showing ERand ribosomesThe endomembrane systemregulates protein traffic and performsmetabolic functions in the cell• Components of the endomembrane system:– Nuclear envelope– Endoplasmic reticulum– Golgi apparatus– Lysosomes– Vacuoles– Plasma membrane• These components are either continuous orconnected via transfer by vesiclesThe Endoplasmic Reticulum:Biosynthetic Factory• The endoplasmic reticulum (ER) accounts formore than half of the total membrane in manyeukaryotic cells• The ER membrane is continuous with thenuclear envelope• There are two distinct regions of ER:– Smooth ER, which lacks ribosomes– Rough ER, with ribosomes studding its surfaceLE 6-12RibosomesSmooth ERRough ERER lumenCisternaeTransport vesicleSmooth ER Rough ERTransitional ER200 nmNuclearenvelopeFunctions of Smooth ER• The smooth ER– Synthesizes lipids– Metabolizes carbohydrates– Stores calcium– Detoxifies poisonFunctions of Rough ER• The rough ER– Has bound ribosomes– Produces proteins and membranes, which aredistributed by transport vesicles– Is a membrane factory for the cell• The Golgi apparatus consists of flattenedmembranous sacs called cisternae• Functions of the Golgi apparatus:– Modifies products of the ER– Manufactures certain macromolecules– Sorts and packages materials into transportvesiclesThe Golgi Apparatus: ShippingandReceiving CenterLE 6-13trans face(“shipping” side ofGolgi apparatus)TEM of Golgi apparatus0.1 µmGolgi apparatuscis face(“receiving” side ofGolgi apparatus) Vesicles coalesce toform new cis Golgi cisternae Vesicles alsotransport certainproteins back to ER Vesicles movefrom ER to Golgi Vesicles transport specificproteins backward to newerGolgi cisternae Cisternalmaturation:Golgi cisternaemove in a cis-to-transdirection Vesicles form andleave Golgi, carryingspecific proteins toother locations or tothe plasma mem-brane for secretionCisternae• In which cell would you expect to find the mostsmooth endoplasmic reticulum?– A. Muscle cell in the thigh muscle of a long-distancerunner– B. Pancreatic cell that manufactures digestiveenzymes– C. Macrophage (white blood cell) that engulfsbacteria– D. Epithelial cells lining the digestive tract– E. Ovarian cell that produces estrogen (a steroidhormone)• In which cell would you expect to find the mostrough endoplasmic reticulum?– A. Muscle cell in the thigh muscle of a long-distancerunner– B. Pancreatic cell that manufactures digestiveenzymes– C. Macrophage (white blood cell) that engulfsbacteria– D. Epithelial cells lining the digestive tract– E. Ovarian cell that produces estrogen (a steroidhormone)Lysosomes: DigestiveCompartments• A lysosome is a membranous sac of hydrolyticenzymes• Lysosomal enzymes can hydrolyze proteins,fats, polysaccharides, and nucleic acids• Lysosomes also use enzymes to recycleorganelles and macromolecules, a processcalled autophagyLE 6-14aPhagocytosis: lysosome digesting food1 µmPlasmamembraneFood vacuoleLysosomeNucleusDigestiveenzymesDigestionLysosomeLysosome containsactive hydrolyticenzymesFood vacuolefuses withlysosomeHydrolyticenzymes digestfood particlesLE 6-14bAutophagy: lysosome breaking down damaged organelle1 µmVesicle containingdamaged mitochondrionMitochondrionfragmentLysosome containingtwo damaged organellesDigestionLysosomeLysosome fuses withvesicle containingdamaged organellePeroxisomefragmentHydrolytic enzymesdigest organellecomponentsVacuoles: DiverseMaintenance Compartments• Vesicles and vacuoles (larger versions ofvacuoles) are membrane-bound sacs withvaried functions• A plant cell or fungal cell may have one orseveral vacuoles• Food vacuoles are formed by phagocytosis• Contractile vacuoles, found in many freshwaterprotists, pump excess water out of cells• Central vacuoles, found in many mature plantcells, hold organic compounds and waterLE 6-155 µmCentral vacuoleCytosolTonoplastCentral vacuoleNucleusCell wallChloroplastThe Endomembrane System:A Review• The endomembrane system is acomplex and dynamic player in thecell’s compartmental organizationLE 6-16-1Nuclear envelopeNucleusRough ERSmooth ERLE 6-16-2Nuclear envelopeNucleusRough ERSmooth ERTransport vesiclecis Golgitrans GolgiLE 6-16-3Nuclear envelopeNucleusRough ERSmooth ERTransport vesiclecis Golgitrans GolgiPlasma membraneThe cytoskeleton is a network offibers that organizes structures andactivities in the cell• The cytoskeleton is a network of fibersextending throughout the cytoplasm• It organizes the cell’s structures and activities,anchoring many organelles• It is composed of three types of molecularstructures:– Microtubules– Microfilaments– Intermediate filamentsLE 6-20MicrotubuleMicrofilaments0.25 µmRoles of the Cytoskeleton:Support, Motility, and Regulation• The cytoskeleton helps to support the cell andmaintain its shape• It interacts with motor proteins to produce motility• Inside the cell, vesicles can travel along “monorails”provided by the cytoskeleton• Recent evidence suggests that the cytoskeleton mayhelp regulate biochemical activitiesLE 6-21aVesicleReceptor formotor proteinMicrotubuleof cytoskeletonMotor protein(ATP powered)ATPLE 6-21b0.25 µmMicrotubule VesiclesComponents of theCytoskeleton• Microtubules are the thickest of the threecomponents of the cytoskeleton• Microfilaments, also called actin filaments, arethe thinnest components• Intermediate filaments are fibers with diametersin a middle rangeMicrotubules• Microtubules are hollow rods about 25 nm indiameter and about 200 nm to 25 microns long• Functions of microtubules:– Shaping the cell– Guiding movement of organelles– Separating chromosomes during cell divisionCentrosomes and Centrioles• In many cells, microtubules grow out from acentrosome near the nucleus• The centrosome is a “microtubule-organizingcenter”• In animal cells, the centrosome has a pair ofcentrioles, each with nine triplets ofmicrotubules arranged in a ringLE 6-220.25


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UCSD BILD 1 - Ribosomes

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