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CHAPTER 4 – ORGANIZATION OF THE CELL THE CELL THEORY Cell theory o Unifying concept that: Cells are the basic living units of organization and function in all organisms All cells come from other cells CELL ORGANIZATION AND SIZE Homeostasis o An appropriate internal environment The organization of all cells is basically similar Plasma membrane o A structurally distinctive surface membrane that surrounds all cells Organelles o Internal structures that are specialized to carry out metabolic processes Cell size is limited Microvilli o Fingerlike projections of the plasma membrane that significantly increase the surface area for absorbing nutrients and other materials Cell size and shape are related to function METHODS FOR STUDYING CELLS Light microscopes are used to study stained or living cells Light microscope (LM) o Consists of a tube with glass lenses at each end o Type used by most students Magnification o The ratio of the size of the image seen with the microscope to the actual size of the object Resolution or Resolving Power o The capacity to distinguish fine detail in an image Electron microscopes provide a high-resolution image that can be greatly magnified Electron microscope (EM) o A type of microscope that permits very high magnification of 250,000 times or more Ultrastructure o The fine details of cells Transmission electron microscope (TEM)
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o An EM where the specimen is embedded in plastic and then cut into extraordinarily thin sections o These thin sections are then viewed Scanning electron microscope (SEM) o Specimen is coated with a thin film of gold or some other metal o Secondary electrons are emitted when the electron beam hits the surface of the specimen o A 3-D picture is given off by the secondary electrons Biologists use biochemical techniques to study cell components Cell fractionation o A technique for purifying different parts of cells so that they can be studied by physical and chemical methods Centrifuge o A device that spins the cell extract and subjects it to centrifugal force Differential centrifugation o The supernatant is spun at successively higher speeds, permitting carious cell components to be separated on the basis of their different sizes and densities Density gradient centrifugation o The centrifuge tube is filled with a series of solutions of decreasing density o The pellet is place in the tube and is spun o The organelles will end up in the place where their density is equal to that of the solution PROKARYOTIC AND EUKARYOTIC CELLS Nuclear area o The limited region of a cell that DNA is located in prokaryotic cells o Not enclosed by a membrane Cells wall o Extracellular structures that enclose the entire cell, including the plasma membrane Flagella o Long fibers that project from the surface of the cell that are important in locomotion Ribosomes o Small complexes of ribonucleic acid (RNA) and protein that synthesize polypeptides
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