lec_22_vis_cells_F05 -...

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Dave Gilmour, 403 S. Frear, 863-8905, [email protected] Class notes are posted on ANGEL.  Review questions will also be posted on  ANGEL. Office hours: Monday 1:30 - 3:30 or by appointment. Exam 3: Nov. 16, in class Exam 4: Friday, Dec. 16, 12:20-1:10 or 1:20-2:10 108 Forum Times for Exam 3 and 4 review sessions: Tuesday, Nov. 15, 7:00 PM Monday, Dec. 12, 7:00 PM
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Chapter 9 Visualizing Cells Read pages: 547-557, 560-565, 574-575 Lecture 22
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A sense of  scale?
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Diameter of a typical animal cell - 10 to 20 microns micron = micrometer = um = 0.001 mm The head of a pin is about 1 mm in diameter so a cell is about 1/100 the  diameter of a pin head
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Diameter of the ribosome - 20 nanometers. Diameter of atom or length of a chemical bond -  0.2 nanometers = 2 angstroms.
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Approximate limit of light  microscopy Microscopy provides a way to view cellular  structures and the behavior of specific  molecules in the context of the cell.
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The “limit of resolution” of resolution is set by the wavelength of irradiation applied to the  sample: light, electrons, X-rays. The limit of resolution is the “limiting separation at which two objects can still be seen as  distinct”.   The limit of resolution is approximately 1/2 the wavelength of the light.   Visible light ranges from 400 nm for violet to 700 nm for red.   Hence, the practical limit of resolution for light microscopy is a few hundred nanometers -  about the size of some bacteria.
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Light microscopy
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To observe a specimen:  •it must absorb particular  wavelengths of light (which  results in color)  •or it must slow the light so that  different paths of light are out of  phase.  
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Bright-field microscopy is poor for  viewing colorless samples such as most  animal cells.
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