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Biology

The Art of Cell Biology - How Are These Images Generated?

Fluorescence is the energy in the form of light that is emitted from a molecule when it is excited. In these images, UV light excited a protein called GFP Green Fluorescent Protein) that emits green light. GFP is isolated from a Jelly Fish, and then introduced genetically into the organism being viewed. Usually the GFP is fused to a protein normally resident in the organism, so that the resident protein is now tagged and can be followed. The energy of fluorescence emission differs between molecules, and thus it is possible to detect a variety of colors, and hence molecules in each specimen. For example, chlorophyll emits red light when excited by UV. Coincident locations yield additional colors. There are two types of microscopes used. The compound fluorescence microscope can detect both white light and fluorescence, but is limited by the amount of material that is in focus; only several υm of thickness is actually in focus, but the instrument captures far more depth and thus out of focus sample create blurry images. The confocal microscope only captures fluorescence, and only a single section of focused light at a time, hence the image is very sharp. The confocal can capture multiple sequential images at different focal planes, and then combine these into a 3D image. Student in Bio 224 over the years have learned to use both microscopes, and capture images of plant and animal cells, typically 20-200 υm in diameter. Students are provided with a plant that has an “unknown” location of the GFP fusion protein, and their task is to identify the cellular location through microscopy and biochemical methods.

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