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BIOL 1020 6

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Auburn University
BIOL 1020
Anne- Marie Singh

BIOL 1020CHAPTER 6 LECTURE NOTES Chapter 6 A tour of the CellI Cell theoryAAll living organisms are composed of cells 1smallest building blocks of all multicellular organisms 2all cells are enclosed by a surface membrane that separates them from other cells and from their environment 3specialized structures with the cell are called organelles many are membranebound BToday all new cells arise from existing cells CAll presently living cells have a common origin 1all cells have basic structural and molecular similarities2all cells share similar energy conversion reactions3all cells maintain and transfer genetic information in DNA 4the genetic code is essentially universal II Cell organization and homeostasisAPlasma membrane surrounds cells and separates their contents from the external environment BCells are heterogeneous mixtures with specialized regions and structures such as organelles CCell size is limited 1surface area to volume ratio puts a limit on cell size food andor other materials must get into the cell waste products must be removed from the cell thus cells need a high surface area to volume ratio but volume increases faster than surface area as cells grow larger 2cell shape varies depending both on function and surface area requirements III Studying cellsmicroscopy and fractionationAMost cells are large enough to be resolved from each other with light microscopes LM 1cells were discovered by Robert Hooke in 1665 he saw the remains of cell walls in cork with a LMs at about 30x magnification 2modern LMs can reach up to 1000x 3LM resolution clarity is limited to about 1 mm due to the wavelength of visible light thus only about 500 times better than the human eye even at maximum magnification 4small cells such as most bacteria are about 1 mm across just on the edge of resolution 5some modifications of LMs and some treatments of cells allow observation of subcellular structure in some cases BResolution of most subcellular structure requires electron microscopy EM 1electrons have a much smaller wavelength than light resolve down to under 1 nm 2magnification up to 250000x or more and resolution over 500000 times better than the human eye 3includes transmission TEM and scanning SEM forms transmissionelectron passes through sample need very thin samples 100 nm or less thick samples embedded in plastic and sliced with a diamond knife scanningsamples are goldplated electrons interact with the surface images have a 3D appearance CCells can be broken and fractionated to separate cellular components for study 1cells are broken lysed by disrupting the cell membrane often using some sort of detergent2grinding and other physical force may be required especially if cell walls are present 3centrifugation is used to separate cellular components using a centrifuge samples are spun at high speeds resulting in exposure to a centrifugal force of thousands to hundreds of thousands times gravity example 500000 x G results in a pellet and supernatant cell components will be in one or the other depending on their individual properties intact membranebound organelles often wind up in pellets depending on their density and the centrifugal force reached more densemore likely in pellet special treatments can determine whether a component ends up in the pellet or supernatant density gradients can also be used to subdivide pellet components based on their density this can be used to separate organelles from each other for example Golgi apparatus from ER IV Eukaryotic vs prokaryotic cells
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