Chapter 6 A Tour of the Cell PowerPoint Lectures for Biology Eighth Edition Neil Campbell and Jane Reece Copyright 2008 Pearson Education Inc publishing as Benjamin Cummings Overview The Fundamental Units of Life 10 m Human height Length of some nerve and muscle cells 0 1 m Chicken egg 1 cm Frog egg 100 m 10 m Most plant and animal cells Nucleus Most bacteria 1 m 100 nm 10 nm 1 nm 0 1 nm Mitochondrion Smallest bacteria Viruses Ribosomes Proteins Lipids Small molecules Atoms Electron microscope 1 mm Light microscope 1m Unaided eye Fig 6 2 Microscopy Use different methods for enhancing visualization of cellular structures TECHNIQUE RESULT a Brightfield 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 50 m b Brightfield stained specimen Staining with various dyes enhances contrast but most staining procedures require that cells be fixed preserved c Phase contrast Enhances contrast in unstained cells by amplifying variations in density within specimen especially useful for examining living unpigmented cells Figure 6 3 Microscopy d Differential interference contrast Nomarski Like phase contrast microscopy it uses optical modifications to exaggerate differences in density making the image appear almost 3D e 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 f 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 m 50 m Fig 6 4 TECHNIQUE a Scanning electron microscopy SEM RESULTS Cilia 1 m Scanning electron microscopy 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 b Transmission electron Longitudinal Cross section section of of cilium microscopy TEM 1 m cilium Transmission electron microscopy 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 The process of cell fractionation APPLICATION Cell fractionation is used to isolate fractionate cell components based on size and density Homogenization Tissue cells TECHNIQUE 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 cell components forming a series of pellets 1000 g Homogenate 1000 times the force of gravity Differential centrifugation 10 min Supernatant poured into next tube 20 000 g 20 min Pellet rich in nuclei and cellular debris RESULTS 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 80 000 g 60 min 150 000 g 3 hr Pellet rich in mitochondria and chloroplasts if cells are from a Pellet rich in plant microsomes pieces of plasma memPellet rich in branes and cells internal ribosomes membranes Figure 6 5 Prokaryotic cells Pili attachment structures on the surface of some prokaryotes Nucleoid region where the cell s DNA is located not enclosed by a membrane Ribosomes organelles that synthesize proteins Bacterial chromosome a A typical rod shaped bacterium Figure 6 6 A B Plasma membrane membrane enclosing the cytoplasm Cell wall rigid structure outside the plasma membrane Capsule jelly like outer coating of many prokaryotes 0 5 m Flagella locomotion organelles of some bacteria b A thin section through the bacterium Bacillus coagulans TEM Plasma Membrane Outside of cell Hydrophilic region Inside of cell 0 1 m Hydrophobic region a TEM of a plasma membrane The plasma membrane here in a red blood cell appears as a pair of dark bands separated by a light band Hydrophilic region Phospholipid Proteins b Structure of the plasma membrane Fig 6 8 Surface area increases while total volume remains constant 5 1 1 Total surface area Sum of the surface areas height width of all boxes sides number of boxes Total volume height width length number of boxes Surface to volume S to V ratio surface area volume 6 150 750 1 125 125 6 1 2 6 Fig 6 9a Animal Cell ENDOPLASMIC RETICULUM ER Flagellum Rough ER Smooth ER Nuclear envelope NUCLEUS Nucleolus Chromatin Centrosome Plasma membrane CYTOSKELETON Microfilaments Intermediate filaments Microtubules Ribosomes Microvilli Golgi apparatus Peroxisome Mitochondrion Lysosome Fig 6 9b NUCLEUS Nuclear envelope Nucleolus Chromatin Plant Cell Rough endoplasmic reticulum Smooth endoplasmic reticulum Ribosomes Central vacuole Golgi apparatus Microfilaments Intermediate filaments Microtubules Mitochondrion Peroxisome Chloroplast Plasma membrane Cell wall Wall of adjacent cell Plasmodesmata CYTOSKELETON Fig 6 10 1 m Nucleus Nucleus Nucleolus Chromatin Nuclear envelope Inner membrane Outer membrane Nuclear pore Pore complex Surface of nuclear envelope Rough ER Ribosome 1 m 0 25 m Close up of nuclear envelope Pore complexes TEM Nuclear lamina TEM Fig 6 11 Ribosomes Cytosol Endoplasmic reticulum ER Free ribosomes Bound ribosomes Large subunit 0 5 m TEM showing ER and ribosomes Small subunit Diagram of a ribosome Fig 6 12 Endoplasmic Reticulum Smooth ER Rough ER ER lumen Cisternae Ribosomes Transport vesicle Smooth ER Nuclear envelope Transitional ER Rough ER 200 nm Fig 6 13 Golgi Apparatus Golgi apparatus cis face receiving side of
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