An Overview of Viruses for Light Microscopists
A 3D modelling article
by Mol Smith 2010
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  Scale  Herpes Virus  T4 Virus  Influenza Virus   Resources and external links
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Viruses - Twilight Life?
Viruses are not generally considered to be living entities. They are large molecular units made up of RNA or DNA contained within a protein shell. Unlike living cells, they lack organelles, ribosomes, cytoplasm, respiratory systems, gas exchange, and a source of energy creation. They are effectively parasites, capable of reproduction only by hijacking living cells and taking over control of their reproduction systems, and forcing them to produce more viruses through DNA replication and protein synthesis.

Viruses for Light Microscopists
Light Microscopists will never see a virus directly using their microscopes, but it is possible to see cells damaged by viruses in stained sections of tissue. This means most enthusiast microscopists are limited in what they see for themselves using their instruments. This is a shame because undoubtedly, most enthusiasts are driven by curiosity and an innate passion to explore the reality they find themselves in. But we can still explore these twilight entities through 3D modelling and by using existing data weaned from SEM microscopists and professional study. I suspect we will not be too interested in the deep workings of the viruses' biochemical processes, or the pathology of the diseases that many of these viruses cause in plants, animals and humans, so I have kept the content of this article to a style which I hope will excite your curiosity, and give everyone a 'SEM*1:-less' vision of the sub-light-microscopical world.

SEM*1: Scanning Electron Microscope - wiki

Reasons for the limitations of Light Microscopes
With a few exceptions (Fluorescence & Confocal Light Microscopy), light/optical microscopes are limited to the defraction of incoherent light by glass lenses. There is a maximum resolution of all optical systems which is due to diffraction. The effect is known as
diffraction limitation: the resolution of a given instrument is proportional to the size of its objective, and inversely proportional to the wavelength of the light being observed. For a given numerical aperture (NA), the resolution of microscopy for flat objects under incoherent illumination can be improved using interferometric microscopy.

Several new techniques from emerging technologies will probably break through the current limit of light microscopy soon by the use of new nano materials to create finer apertures, and the application of coherent light sources like lasers: the beam of coherent light is different from other light sources emitting incoherent light beams ( tungsten lamps, LEDs ). Our 'normal' light sources are of random phase - varying with time and position; whereas a laser light is a narrow-wavelength,monochromatic light (
although there are lasers that emit a broad spectrum light at different wavelengths ).

The limitation of an average light microscope ( quality of the instrument may vary this only very slightly ) is to be able to resolve an entity 0.3 microns
*2 across (300nm). Viruses are typically in almost all cases smaller than this. There are exceptions though! The smallpox virus is exactly this size - 0.3 microns (3 µm*3), and a unique viruses discovered in 1992 is a whopping size at 800 nm (0.8 microns): the MimiVirus! This is actually visible in a light microscope, although like a star in the sky to an average telescope, it will be discerned as no more than the tiniest of specks. It is the largest known Virus, larger than some bacterium. It has been placed in a new family of viruses - the Mimiviridae*x.

*2 A micron, which is a micrometer, is normally stated as µm
*3 Microns to nm (nanometres - english spelling) conversions here
*x Offsite link to viralzone web site

The best way for a light microscopist to understand the size of nearly all viruses, compared to the size of non-viral microscopic forms, is to present one (a virus) side-by-side to an entity familiar to the microscopist: so, what about the Euglena? Most of us are familiar with this protozoan
*x. Here we are then - a Herpes Virus next to the Euglena Protozoan, by the application of 3D modelling. The image below shows a slightly exaggerated blue dot representing the Herpes Virus: it is shown here 4x larger than it really is. Had I shown it at its full size, it would not be visible at this scale. Please take note that this image, and the movie just below it, may be in the order of 10x error plus or minus in what you see, with respect to the real world, due to issues with presenting accurately sized images in this way on the internet; a process prone to 'averaging', image pixel issues, and dpi problems. But hopefully it will give you a much better understanding than by using your imagination alone.

*x Protozoa offsite link

Fig. 1

And since you will have certainly turned up the magnification on your light microscope to take a better look at Protozoa and other pond-life forms, here is the Herpes virus as it would appear under your 'scope' if you could see it next to the Euglena and zoom in...
Note: the accuracy of scale is + or - x10 )

Note: this is a movie. Please wait for it to load fully!

So now we have a better understanding of the size and scale of Viruses compared to what we would normally explore under a microscope, I think it's still frustrating not to see this Virus close up, so let us
take a closer look here...


Comments to the author
Mol Smith are welcomed.

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Published in Mar 2010 Micscape Magazine.
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