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Running head:MACROMOLECULAR AND CELL BIOLOGYMacromolecular and Cell BiologyName of the StudentName of the UniversityAuthor Note
1MACROMOLECULAR AND CELL BIOLOGYElectron Microscopy of sub cellular structure1.0 AbstractThe discovery of the first electromagnetic lens in 1931 made electron microscopy aninteresting and remarkable tool to study cell structures as it eliminates the barriers to highresolution imposed by the visible light limitations. It made it easier to study the biological ultrastructures as well as microorganisms smaller than the bacteria. The report briefly presents thelimitations of the light microscope and the principle of the electron microscope. Further, thereport explores the application of the electron microscopy to study the Golgi apparatus whichwas discovered in 1898 by light microscope, but itsultra-structure compositionwas unknown,subjectingit to electron microscopic investigation.2.0 Introduction2.1 Electron microscopyMax Knoll and Ernst Ruska of Germany discovered electron microscope in 1931 (Pease,2013). Starting with the theoretical resolution of 10 nm the electron microscopes built in 1944reduced to 2nm. Between 1930-1960, several modifications were made to finally build theelectron microscope with better lenses, resolution improving and brighter electron guns forproducing higher energy and velocity electrons for sample probing. The period 1960-2000marks the innovation of different types of electron microscope such as scanning andTransmission electron microscope (Humphreys, Beanland & Goodhew, 2014).
2MACROMOLECULAR AND CELL BIOLOGYThe fundamental limitations of all the microscopes lay in the difficulty to probe structuraldetails of cells with a given type of radiation as they are smaller than own wavelength. Opticalmicroscopy lacks high resolution. It limited its use in many areas of scientific research althoughit was the first microscope used for studying structures of mitochondria and bacteria, which wasset at the wavelength of visible light. However, smaller details could not be visualized by lightmicroscope due to affects of the wave nature of light. Electron microscope eliminates thelimitations of the light microscope by providing high-resolution image of the sample. In lightmicroscope, optical lenses cannot obtain high magnification. Therefore, it is useful for thestudying the biological ultra structures and discern even macromolecules.. It would not havebeen possible for biologists to view the submicroscopic cells organelles like endoplasmicreticulum, ribosomes, and centrioles or the internal structure of the organelles like mitochondria.Electron microscopy also made it possible to study virus and viroids (Spence, 2013).2.2 Principles of Electron microscopyThe general principle of the electron microscope and the light microscope is same.Electron microscope uses the electron beams, as the source of illumination. Instead of light, highvelocity electrons are allowed to travel in a vacuum tube. Electrons revolve around atomicnucleus and fly off from atom when excited by the heat energy. High voltage current is used toheat tungsten to release stream of electrons like light beam. A series of electromagnetic lensesare used to focus the beam of electrons. It works in contrast to the eye and objective piece lensesand condenser in the light microscope. The magnified image obtained from the object positionedbetween objective and condenser is visible on photographic plate or on fluorescent screen.However, on light microscope it is observed through eyepiece. The image obtained by electron
3MACROMOLECULAR AND CELL BIOLOGYmicroscope has shades of black, grey or white as electrons are colorless. Fluorescent screen isused to observe the final image as electrons cannot be viewed by naked eye (De Boer et al.,2015).Cross section of electron microscope (Source: http://www.visualdictionaryonline.com)The wavelengths of the electrons are 100,000 times shorter than the visible light.Therefore, it has high resolution to detect details of smaller objects, even with small numericalaperture. The resolving power increases with the decreasing wavelength of light. For instance