Chapter 6 modified

Chapter 6 modified - Chapter 6- A tour of the cell The cell...

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Chapter 6- A tour of the cell The cell is the simplest collection of matter that can live. The cell is a microcosm. There is structural order in cells and from these stem emergent properties. Cells sense and respond to environmental fluctuations. Cells have the ability to evolve and cells present today are the modified versions of earlier ones. Cytology is the study of cell structure. Microscopy A. Light microscopes: Visible light is passed through the specimen and then through glass lenses. The image is magnified as it is projected onto eye, film or digital sensor. Magnification in microscopy is the ratio of an object’s image size to its real size. Resolution is the measure of clarity of the image, i.e. the min distance 2 pts can be separated and still distinguished as 2 pts. Resolution power of light microscopes- 0.2 micrometers to 200 nanometers. Light microscopes can magnify an image up to 1000 times, but as the magnification increases, the image becomes increasingly blurry. Can see up to the smallest bacteria. B. Electron microscopes: Focuses a beam of electrons through the specimen or onto its surface. Resolution is inversely related to the wavelength of the specimen studied, approx 2 nm limit. Cell ultrastructure is the cell’s anatomy as revealed by an electron microscope. Two basic types o Scanning Electron Microscope (SEM). Provides a detailed study of the surface of the specimen. The electron beam scans the surface of the sample which is usually coated with a layer of thin gold foil. Electrons on the surface are excited and are then detected by a device than converts the electronic signal to a display on the video screen. The result is called the topography of the specimen and it appears 3- dimensional. o Transmission Electron Microscope (TEM). Studies internal ultrastructure of cells. The electron beam is aimed through a thin section of the specimen. The cells are stained with atoms of heavy metals which attach to certain structures, increasing their electron density. The electron beam is scattered more in the denser areas. The image is created by the pattern of transmitted electrons. Electron microscopes reveal many organelles that are unable to be seen by a light microscope. A disadvantage of the electron microscopes is that the method used to prepare specimen cells normally kills the cells. Cell Fractionation: We use cell fractionation to take cells apart and separate the major organelles from one another in terms of size and density. The centrifuge is the instrument used. It spins test tubes holding mixtures at
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various speeds. First cells are homogenized in a blender to break them up. Then the mixture is then centrifuged forming a series of pellets. Hierarchy of pellets produced.
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Chapter 6 modified - Chapter 6- A tour of the cell The cell...

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