BIS 1A - BIS 1A Cell Theory (Cell theory originated in...

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BIS 1A Cell Theory (Cell theory originated in 1800s, zoologist and botanist (Belgian and a German). Realized that they were seeing the same things, same sort of box like structure in many types of organisms. Microscopes invented in 1600) -Cells are the simplest bits of living material, ie of material that has all the characteristics of life -all organisms are cells, or can be subdivided into cells -all cells come from pre-existing cells (you don’t see spontaneous generation of life under existing conditions) -most cells are too small to see (50 micrometers, mu m, 10^-6 meters in diameter) Light Microscopy Advantages: simple: can be used for live, functioning cells (though not at 1000x) Disadvantages: resolution limited by (a)lack of contrast, (b) thick subjects: light- scattering, (c) wavelength of light (natural limit of resolution—1/2 wavelength used, ca 0.2 mu m with blue light) Solutions: (a) fixation (keep things from moving around, do it chemically with something like formaldehyde), (b) embedding and sectioning(put specimen in a stiffening material and then take a very sharp microtome(sp?) knife and cut a small section), (c) staining(things that bind with different components of the cell so you can see different parts), (d)Confocal illumination (use a laser to scan the object) There are several variations of light microscopy Goal: improved contrast, minimized scattering Research method: Bright-field microscopy, phase-contrast micrscopy, differential interference-contrast microscopy, fluorescence microscopy, confocal microscopy, stained bright field microscopy Electron microscope replaces thelight beam with a beam of electrons and the glass lenses with charged or magnetic ciols that bend electron movement (see pictures from slide) Electron Microscopy Use magnets to bend and electron beam, ie light with shorter wavelength 10^-4 micrometers Advantage: high resolution (because of shorter wavelength) Disadvantage: must trea sample to resist electrons and vacuum; must slice very thin Solutions: (a)Fixation (b)embedding; slicing;staining (osmium tetroxide, uranyl acetate), (c)scanning electron microscopy(when the electron beam scans the surface and you see what scatters back, a computer puts a picture of the surface) See slides for pictures:
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Cryoelectron microscopy: freezing an electron really fast (fractions of a second) so that it can’t be changed, as opposed to theory that you aren’t looking at a normal cell when you use other methods that involve chemical treatment Cell fractionation isolates quantities of cell parts (one way to do so is with a centrifuge) Strategy: Grind up cells (break open without detorying parts), separate parts by size (e.g. centrifugation)
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This note was uploaded on 01/20/2011 for the course BIS 1A taught by Professor Gearhart during the Spring '07 term at UC Davis.

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BIS 1A - BIS 1A Cell Theory (Cell theory originated in...

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