Ch. 6 notes

Ch. 6 notes - Ch 6 14:47 Cells fundamental unit of life...

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Ch. 6 14:47 Cells – fundamental unit of life Light microscopes (LM) – visible light is passed through the specimen and then through glass lenses, which refract the light so that the specimen is magnified as it is projected into the eye/camera Magnification – ratio of an object’s image size to its real size Resolution – measure of the clarity of the image; minimum distance 2 points can be separated and still be distinguished as two points Contrast – accentuates differences in parts of the sample Study organelles – the membrane-enclosed structures within eukaryotic cells Electron microscope (EM) – focuses a beam of electrons through the specimen or onto its surface Resolution is inversely related to the wavelength of the radiation a microscope uses for imaging, and electron beams have shorter wavelengths than visible light higher resolution Scanning electron microscope (SEM) – useful for detailed study of the topography of a specimen Electron beam scans the surface of the sample, usually coated with a thin film of gold The beam excites electrons on the surface, and these secondary electrons are detected by a device that translates the pattern of electrons into an electronic signal to a video screen 3-D image Transmission electron microscope (TEM) – studies the internal structure of cells Aims an electron beam through a very thin section of the specimen, which has been stained with atoms of heavy metals, which attach to certain cellular structures, thus enhancing the electron density of some parts of the cell more than others The electrons passing through the specimen are scattered more in the denser regions, so fewer electrons are transmitted The image displays the pattern of transmitted electrons Uses electromagnets instead of glass lenses Light electron microscopes Can study living cells But the methods used to prepare the specimen kill the cells Advances
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Labeling individual cellular molecules/structures with fluorescent marker more detail New techniques/labeling molecules “super resolution microscopy” (can see structures as small as 10-20 nm) Cell fractionism – takes cells apart and separates major organelles and other subcellular structures from one another Centrifuge – spins test tubes holding mixtures of disrupted cells at a series of increasing speeds. At each speed, the force causes some parts of the cell to go to the bottom as a pellet. At lower speeds, you get a pellet with larger components. At higher speeds, smaller components. Cells: basic features Plasma membrane Cytosol – semifluid, jellylike substance in which subcellular components are suspended (cytoplasm = interior of cell) Chromosomes – carry genes in the form of DNA Ribosomes – tiny complexes that make proteins according to instructions from the genes Eukaryotic cells – DNA is inside the nucleus, double membrane Prokaryotic cells – DNA is concentrated in nucleoid (not membrane-enclosed) Differences
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This note was uploaded on 03/14/2012 for the course BISC 220 taught by Professor Mcclure during the Spring '09 term at USC.

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Ch. 6 notes - Ch 6 14:47 Cells fundamental unit of life...

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