DrubinLecture16_2-29-08 - Drubin Lecture 16 Visualizing...

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Drubin - Lecture 16 Visualizing Cells: principles of microscopy I. Visualizing cells All but the largest cells are too small to see with the naked eye. The invention of the compound microscope allowed cells to be visualized for the first time (in 1655!) and thus marked the birth of the field of cell biology. Microscopy still plays a central role in advancing our understanding the function of cells, organelles and proteins. Over the years microscopists have struggled to overcome technical challenges that include maximizing resolution and enhancing contrast. II. Principles of microscopy Magnification: increase in size. Resolution: the ability to distinguish two very closely spaced objects as separate from one another. The limit of resolution of the light microscope is 0.2μm. Enhancing contrast: Most cellular structures and organelles are not colored and absorb light to the same extent, making them difficult to distinguish under a light microscope. Staining can be used to visualize structures within fixed cells. Phase contrast microscopy and differential interference contrast microscopy (DIC or Nomarski) were developed to study living cells without staining. Both DIC and phase contrast microscopy are useful for viewing living cells. III. Video Microscopy Using DIC or phase contrast microscopy, cells can be filmed over time to make time-lapse movies. Although this process is generally referred to as video microscopy, in the last few years video technology has been replaced by digital imaging and computer technology. The ability to visualize cell behavior over time has been especially important for studying dynamic cellular processes such as cell division and cell motility.
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