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Exam 1 Study Guide - Science 23 April 2010 Vol 328 no 5977...

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Science 23 April 2010: Vol. 328. no. 5977, pp. 498 – 501 Stoichiometry and Architecture of AcGve DNA ReplicaGon Machinery in Escherichia coli Rodrigo Reyes-­‐-­‐-­‐Lamothe, 1 David J. Sherra], 1 Mark C. Leake 1,2, The mul0protein replisome complex that replicates DNA has been extensively characterized in vitro, but its composi0on and architecture in vivo is unknown. Using millisecond single-­‐-­‐-­‐molecule fluorescence microscopy in living cells expressing fluorescent deriva0ves of replisome components, we have examined replisome stoichiometry and architecture. Ac0ve Escherichia coli replisomes contain three molecules of the replica0ve polymerase, rather than the historically accepted two. These are associated with three molecules of , a clamp loader component that trimerizes polymerase. Only two of the three sliding clamps are always
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associated with the core replisome. Single-­‐-­‐-­‐strand binding protein has a broader spa0al distribu0on than the core components, with 5 to 11 tetramers per replisome. This in vivo technique could provide single-­‐-­‐-­‐molecule insight into other molecular machines. 15. Heavy atoms such as gold are used to coat samples for Transmission electron microscopy Scanning electron microscopy Fluorescence microscopy Dark-­‐-­‐-­‐field microscopy A student prepares two slides of culture for analysis under the microscope. She does a Gram stain and an Acid-­‐-­‐-­‐fast stain. She makes the following observa0ons: The cells are blue/purple ager the Gram stain is complete. The cells are red ager the Acid-­‐-­‐-­‐fast stain is complete.
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Carbol fuchsin was used as the primary stain. 3) The cells appear to be rods. 16. Themicroorganismis A pathogen Gram-­‐-­‐-­‐posi0ve Gram-­‐-­‐-­‐nega0ve Streptococcus mutans Dyes and Staining Acid-­‐-­‐-­‐fast Stain Used to stain organisms that resist conven0onal staining Par0cularly useful to stain members of genus Mycobacterium High lipid concentra0on in cell wall prevents uptake of dye, ‘Waxy’ mycolic acid
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Use heat to facilitate staining Once stained difficult to decolorize Acid-­‐-­‐-­‐fast stain Presump0ve iden0fica0on in diagnosis of clinical specimens Requires mul0ple steps Primary dye Carbol fuchsin Colors acid-­‐-­‐-­‐fast bacteria red Decolorizer Generally acid alcohol Removes stains from non acid-­‐-­‐-­‐fast bacteria Counter stain Methylene blue Colors non acid-­‐-­‐-­‐fast bacteria blue Primary dye Dyes and Staining Panel A is a Acid-­‐-­‐-­‐fast and Panel B is a Gram staining of Nocardia Nocardia is a Gram posi0ve.
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Is Nocardia Acid-­‐-­‐-­‐fast?
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