Chapter 4.rtf - Chapter 4 Cellular Level of Organization...

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Chapter 4 Cellular Level of Organization Detailed study of the cell began in the 1830s; some of the scientists contributing to the understanding of cell structure and function were Robert Brown, Matthais Schleiden, Theodor Schwann, and Rudolph Virchow. Cell Theory A unifying concept in biology Originated from the work of biologists Schleiden and Schwann in 1838-9 States that: All organisms are composed of cells German botanist Matthais Schleiden in 1838 German zoologist Theodor Schwann in 1839 All cells come only from preexisting cells German physician Rudolph Virchow in 1850’s Smallest unit of life Cell Size Most much smaller than one millimeter (mm) Some as small as one micrometer (mm) Size restricted by Surface/Volume (S/V) ratio Surface is membrane, across which cell acquires nutrients and expels wastes Volume is living cytoplasm, which demands nutrients and produces wastes As cell grows, volume increases faster than surface Cells specialized in absorption modified to greatly increase surface area per unit volume Microscopy Today: Compound Light Microscope Light passed through specimen Focused by glass lenses Image formed on human retina Max magnification about 1000X Resolves objects separated by 0.2 mm, 500X better than human eye Microscopy Today: Transmission Electron Microscope Abbreviated T.E.M. Electrons passed through specimen Focused by magnetic lenses Image formed on fluorescent screen Similar to TV screen Image is then photographed Resolves objects separated by 0.00002 mm, 100,000X better than human eye Microscopy Today: Scanning Electron Microscope Abbreviated S.E.M. Specimen sprayed with thin coat of metal Electron beam scanned across surface of specimen Metal emits secondary electrons Emitted electrons focused by magnetic lenses
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Image formed on fluorescent screen Similar to TV screen Image is then photographed Microscopy Today: Immunofluorescence Light Microscope Antibodies developed against a specific protein Fluorescent dye molecule attached to antibody molecules Specimen exposed to fluorescent antibodies Ultra-violet light (black ligt) passed through specimen Fluorescent dye glows in color where antigen is located Emitted light is focused by glass lenses onto human retina Allows mapping distribution of a specific protein in cell Microscopy Today: Confocal Microscopy Narrow laser beam scanned across transparent specimen Beam is focused at a very thin plane Allows microscopist to optically section a specimen Sections made at different levels Allows assembly of 3D image on computer screen that can be rotated Microscopy Today: Video-enhanced Contrast Microscopy Great for specimens with low contrast, like living cells Image is captured by TV camera instead of eye Image is then “tweaked” by adjusting contrast Darkest part of image is made black
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