Chapter 6Overview: The Fundamental Units of LifeSlide 3MicroscopySlide 5Slide 6The process of cell fractionationProkaryotic cellsPlasma MembraneSlide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18The Endomembrane System: A ReviewSlide 20Slide 21Peroxisomes: OxidationCytoskeletonSlide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Plasmodesmata in Plant CellsSlide 33Slide 34You should now be able to:Slide 36Copyright © 2008 Pearson Education, Inc. publishing as Benjamin CummingsPowerPoint Lectures for Biology, Eighth EditionNeil Campbell and Jane ReeceChapter 6Chapter 6A Tour of the CellOverview: The Fundamental Units of LifeFig. 6-210 m1 m0.1 m1 cm1 mm100 µm10 µm1 µm100 nm10 nm1 nm0.1 nmAtomsSmall moleculesLipidsProteinsRibosomesVirusesSmallest bacteriaMitochondrionNucleusMost bacteriaMost plant and animal cellsFrog eggChicken eggLength of some nerve and muscle cellsHuman heightUnaided eyeLight microscopeElectron microscope–Use different methods for enhancing visualization of cellular structuresTECHNIQUE RESULTBrightfield (unstained specimen). Passes light directly through specimen. Unless cell is naturally pigmented or artificially stained, image has little contrast. [Parts (a)–(d) show a human cheek epithelial cell.](a)Brightfield (stained specimen). Staining with various dyes enhances contrast, but most staining procedures require that cells be fixed (preserved).(b)Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living, unpigmented cells.(c)50 µmFigure 6.3MicroscopyDifferential-interference-contrast (Nomarski). Like phase-contrast microscopy, it uses optical modifications to exaggerate differences indensity, making the image appear almost 3D.Fluorescence. Shows the locations of specific molecules in the cell by tagging the molecules with fluorescent dyes or antibodies. These fluorescent substances absorb ultraviolet radiation and emit visible light, as shown here in a cell from an artery.Confocal. Uses lasers and special optics for “optical sectioning” of fluorescently-stained specimens. Only a single plane of focus is illuminated; out-of-focus fluorescence above and below the plane is subtracted by a computer. A sharp image results, as seen in stained nervous tissue (top), where nerve cells are green, support cells are red, and regions of overlap are yellow. A standard fluorescence micrograph (bottom) of this relatively thick tissue is blurry.50 µm50 µm(d)(e)(f)MicroscopyFig. 6-4(a) Scanning electron microscopy (SEM)TECHNIQUE RESULTS(b) Transmission electron microscopy (TEM)CiliaLongitudinalsection ofciliumCross sectionof cilium1 µm1 µmScanning electron micro-scopy (SEM). Micrographs taken with a scanning electron microscope show a 3D image of the surface of a specimen. This SEM shows the surface of a cell from a rabbit trachea (windpipe) covered with motile organelles called cilia. Beating of the cilia helps move inhaled debris upward toward the throat.Transmission electron micro-scopy (TEM). A transmission electron microscope profiles a thin section of a specimen. Here we see a section through a tracheal cell, revealing its ultrastructure. In preparing the TEM, some cilia were cut along their lengths, creating longitudinal sections, while other cilia were cut straight across, creating cross sections.Cell fractionation is used to isolate (fractionate) cell components, based on size and density. First, cells are homogenized in a blender to break them up. The resulting mixture (cell homogenate) is then centrifuged at various speeds and durations to fractionate the cellcomponents, forming a series of pellets. APPLICATIONTECHNIQUEFigure 6.5TissuecellsHomogenizationHomogenate1000 g(1000 times theforce of gravity)10 minDifferential centrifugationSupernatant pouredinto next tube20,000 g20 minPellet rich innuclei andcellular debrisPellet rich inmitochondria(and chloro-plasts if cellsare from a plant)Pellet rich in“microsomes”(pieces of plasma mem-branes andcells’ internalmembranes)Pellet rich inribosomes150,000 g3 hr80,000 g60 min In the original experiments, the researchers used microscopy to identify the organelles in each pellet, establishing a baseline for further experiments. In the next series of experiments, researchers used biochemical methods to determine the metabolic functions associated with each type of organelle. Researchers currently use cell fractionation to isolate particular organelles in order to study further details of their function.RESULTSThe process of cell fractionationProkaryotic cells(b) A thin section through the bacterium Bacillus coagulans (TEM)Pili: attachment structures onthe surface of some prokaryotesNucleoid: region where thecell’s DNA is located (notenclosed by a membrane)Ribosomes: organelles thatsynthesize proteinsPlasma membrane: membraneenclosing the cytoplasmCell wall: rigid structure outsidethe plasma membraneCapsule: jelly-like outer coatingof many prokaryotesFlagella: locomotionorganelles ofsome bacteria(a) A typical rod-shaped bacterium 0.5 µmBacterialchromosomeFigure 6.6 A, BOutside of cellInside of cellHydrophilicregionHydrophobicregionHydrophilicregion(b) Structure of the plasma membrane PhospholipidProteinsTEM of a plasmamembrane. Theplasma membrane,here in a red bloodcell, appears as apair of dark bandsseparated by alight band.(a)0.1 µmPlasma MembraneFig. 6-8Surface area increases whiletotal volume remains constant5116150 750125 1251661.2Total surface area[Sum of the surface areas(height width) of all boxessides number of boxes]Total volume[height width length number of boxes]Surface-to-volume(S-to-V) ratio[surface area ÷ volume]Fig. 6-9aENDOPLASMIC RETICULUM (ER)Smooth ERRough ERFlagellumCentrosomeCYTOSKELETON:MicrofilamentsIntermediatefilamentsMicrotubulesMicrovilliPeroxisomeMitochondrionLysosomeGolgiapparatusRibosomesPlasma membraneNuclearenvelopeNucleolusChromatinNUCLEUSAnimal CellFig. 6-9bNUCLEUSNuclear envelopeNucleolusChromatinRough endoplasmic reticulumSmooth endoplasmic reticulumRibosomesCentral vacuoleMicrofilamentsIntermediate filamentsMicrotubulesCYTO-SKELETONChloroplastPlasmodesmataWall of adjacent cellCell wallPlasma membranePeroxisomeMitochondrionGolgiapparatusPlant CellFig. 6-10NucleolusNucleusRough ERNuclear lamina (TEM)Close-up of nuclear envelope1 µm1 µm0.25 µmRibosomePore
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