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To defeat Covid-19, scientists try to "see" the invisible enemy



However, the CDC image is far from the overall picture. For one thing, not every virus particle is identical. Researchers have now observed that some virus particles are spherical while others are egg-shaped. Their sizes vary with diameters between 80 and 160 nanometers. Lined up side by side, almost 1,000 corona viruses would fit across the width of an eyelash.

Courtesy of CDC

In addition, the envelope of the virus is not really gray and its spikes are not red – the pathogen is too small to be colored. What people perceive as color is primarily the result of light waves that are reflected from or absorbed by the surfaces of objects. However, the corona virus is smaller than the visible light. Its diameter is about three times narrower than the wavelength range of violet light, the visible light with the shortest wavelengths.

"It's a very artistic interpretation," says Alissa Eckert, the medical illustrator who created the CDC portrait with a colleague Dan Higgins. "It is intentionally simplified what communicates best."

The design of drugs and vaccines requires much more scientifically precise images. Researchers magnify the microbe by more than 40,000 times and take extreme close-ups to understand its structural subtleties. For example, biologist Jason McLellan of the University of Texas at Austin and his team released high-magnification 3D images of the coronavirus spike protein in February.

The team did not examine the spike protein as it exists in the wild on the surface of a real virus. Instead, they mimicked the part of the genome of the virus that scientists in China released publicly on January 11 that contained the instructions for making the protein. McLellan's team inserted these genes into cultured human embryonic kidney cells, which then produced these spike proteins. They extracted these proteins and imaged them.

McLellan's team imaged the protein tip using a method known as cryo-electron microscopy, in which they fired a thin electron beam at frozen, single proteins that adhered to a fine network. The electrons that move near the speed of light hit the atoms of the protein with a detector. The resulting pattern on the detector forms an image. The researchers repeated the process to create thousands of images of proteins on the web, all oriented in different directions. "They then use algorithms to try to recreate the object that could give all of these different views," says McLellan.

Read all of our corona virus coverage here.

Other researchers also use a method called X-ray crystallography to examine the structure of the virus. In this method, they take multiple copies of the biological molecule in question and arrange them in clean rows to form a crystal. Then they radiate X-rays on the crystal and can deduce the structure of the virus from the shadow and brightness areas that are formed by the transmitted X-rays. They use the crystalline form of the molecules because it reduces the number of X-rays to be used. X-rays can break the molecule into pieces if used at too high a dose. (Rosalind Franklin discovered the double helix structure of DNA using X-ray crystallography.)


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