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Viruses are subcellular entities that infect organisms from all different kingdoms of life. In their simplest form they are just constituted by an infective genetic.
Table of contents

• First video of viruses assembling released
• Some physics of viruses and the grand questions still unanswered
• The Physics of Viruses

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Fetching data from CrossRef. This may take some time to load. Jump to main content. Jump to site search. Journals Books Databases. Search Advanced. Current Journals. Archive Journals. All Journals. Viruses occupy a special taxonomic position: they are not plants, animals, or prokaryotic bacteria single-cell organisms without defined nuclei , and they are generally placed in their own kingdom. In fact, viruses should not even be considered organisms, in the strictest sense, because they are not free-living; i.

The nucleic acid encodes the genetic information unique for each virus. The infective, extracellular outside the cell form of a virus is called the virion. It contains at least one unique protein synthesized by specific genes in the nucleic acid of that virus. In virtually all viruses, at least one of these proteins forms a shell called a capsid around the nucleic acid.

Certain viruses also have other proteins internal to the capsid; some of these proteins act as enzymes , often during the synthesis of viral nucleic acids. Other viruslike particles called prions are composed primarily of a protein tightly complexed with a small nucleic acid molecule. Prions are very resistant to inactivation and appear to cause degenerative brain disease in mammals, including humans. Viruses are quintessential parasites ; they depend on the host cell for almost all of their life-sustaining functions.

Unlike true organisms, viruses cannot synthesize proteins, because they lack ribosomes cell organelles for the translation of viral messenger RNA mRNA; a complementary copy of the nucleic acid of the nucleus that associates with ribosomes and directs protein synthesis into proteins. Viruses must use the ribosomes of their host cells to translate viral mRNA into viral proteins. Viruses are also energy parasites; unlike cells, they cannot generate or store energy in the form of adenosine triphosphate ATP.

The virus derives energy, as well as all other metabolic functions, from the host cell. The invading virus uses the nucleotides and amino acids of the host cell to synthesize its nucleic acids and proteins, respectively. Some viruses use the lipids and sugar chains of the host cell to form their membranes and glycoproteins proteins linked to short polymers consisting of several sugars. In many viruses, but not all, the nucleic acid alone, stripped of its capsid, can infect transfect cells, although considerably less efficiently than can the intact virions.

The virion capsid has three functions: 1 to protect the viral nucleic acid from digestion by certain enzymes nucleases , 2 to furnish sites on its surface that recognize and attach adsorb the virion to receptors on the surface of the host cell, and, in some viruses, 3 to provide proteins that form part of a specialized component that enables the virion to penetrate through the cell surface membrane or, in special cases, to inject the infectious nucleic acid into the interior of the host cell.

Logic originally dictated that viruses be identified on the basis of the host they infect. This is justified in many cases but not in others, and the host range and distribution of viruses are only one criterion for their classification. It is still traditional to divide viruses into three categories: those that infect animals, plants, or bacteria. Virtually all plant viruses are transmitted by insects or other organisms vectors that feed on plants.

The hosts of animal viruses vary from protozoans single-celled animal organisms to humans. High-speed tracking of single particles is a gateway to understanding physical, chemical, and biological processes at the nanoscale.

Some physics of viruses and the grand questions still unanswered

It is also a major experimental challenge, particularly for small, nanometer-scale particles. Although methods such as confocal or fluorescence microscopy offer both high spatial resolution and high signal-to-background ratios, the fluorescence emission lifetime limits the measurement speed, while photobleaching and thermal diffusion limit the duration of measurements.

Here we present a tracking method based on elastic light scattering that enables long-duration measurements of nanoparticle dynamics at rates of thousands of frames per second.

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The diffusing particles in this cylindrical geometry are continuously illuminated inside the collection focal plane. We show that the method can track unlabeled dielectric particles as small as 20 nm as well as individual cowpea chlorotic mottle virus CCMV virions—26 nm in size and 4.

Our setup is easily incorporated into common optical microscopes and extends their detection range to nanometer-scale particles and macromolecules. The ease-of-use and performance of this technique support its potential for widespread applications in medical diagnostics and micro total analysis systems. Using the components of a particularly well-studied plant virus, cowpea chlorotic mottle virus CCMV , we demonstrate the synthesis of virus-like particles VLPs with one end of the packaged RNA extending out of the capsid and into the surrounding solution.

This construct breaks the otherwise perfect symmetry of the capsid and provides a straightforward route for monofunctionalizing VLPs using the principles of DNA nanotechnology.

It also allows physical manipulation of the packaged RNA, a previously inaccessible part of the viral architecture. Our synthesis does not involve covalent chemistry of any kind; rather, we trigger capsid assembly on a scaffold of viral RNA that is hybridized at one end to a complementary DNA strand. We show that the nucleic acid protruding from the capsid is capable of binding free DNA strands and DNA-functionalized colloidal particles.

We believe this self-assembly strategy can be adapted to viruses other than CCMV. Skip to main content. Main Menu Utility Menu Search. See also: Current research areas , Virus physics. Publications Goldfain, A. The Journal of Physical Chemistry B , , —