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Tobacco Mosaic Virus: The type species of Tobamovirus which causes mosaic disease of tobacco. Transmission occurs by mechanical inoculation.

What are Viruses?

JoVE 10821

A virus is a microscopic infectious particle that consists of an RNA or DNA genome enclosed in a protein shell. It is not able to reproduce on its own: it can only make more viruses by entering a cell and using its cellular machinery. When a virus infects a host cell, it removes its protein coat and directs the host’s machinery to transcribe and translate its genetic material. The hijacked cell assembles the replicated components into thousands of viral progeny, which can rupture and kill the host cell. The new viruses then go on to infect more host cells. Viruses can infect different types of cells: bacteria, plants, and animals. Viruses that target bacteria, called bacteriophages (or phages), are very abundant. Current research focuses on phage therapy to treat multidrug-resistant bacterial infections in humans. Viruses that infect cultivated plants are also highly studied since epidemics lead to huge crop and economic losses. Viruses were first discovered in the 19th century when an economically-important crop, the tobacco plant, was plagued by a mysterious disease—later identified as Tobacco mosaic virus. Animal viruses are of great importance both in veterinary research and in medical research. Moreover, viruses underlie many human diseases, ranging from the common cold, chickenpox, and herpes, to more dangerous infection

 Core: Viruses

Viral Structure

JoVE 10822

Viruses are extraordinarily diverse in shape and size, but they all have several structural features in common. All viruses have a core that contains a DNA- or RNA-based genome. The core is surrounded by a protective coat of proteins called the capsid. The capsid is composed of subunits called capsomeres. The capsid and genome-containing core are together known as the nucleocapsid.

Many criteria are used to classify viruses, including capsid design. Most viruses have icosahedral or helical capsids, although some viruses have developed more complex capsid structures. The icosahedral shape is a 20-sided, quasi-spherical structure. Rhinovirus, the virus that causes the common cold, is icosahedral. Helical (i.e., filamentous or rod-shaped) capsids are thin and linear, resembling cylinders. The nucleic acid genome fits inside the grooves of the helical capsid. Tobacco mosaic virus, a plant pathogen, is a classic example of a helical virus. Some viruses have capsids that are enclosed by an envelope of lipids and proteins outside of the capsid. This viral envelope is not produced by the virus but is acquired from the host’s cell. These envelope molecules protect the virus and mediate interactions with the host’s cells. The viral capsid not only protects the virus’s genome, but it also plays a critical role in interactions with host cells. For i

 Core: Viruses

Transforming, Genome Editing and Phenotyping the Nitrogen-fixing Tropical Cannabaceae Tree Parasponia andersonii

1Laboratory of Molecular Biology, Department of Plant Sciences, Wageningen University & Research, 2Center of Technology for Agricultural Production, Agency for the Assessment and Application of Technology (BPPT), 3Department of Ecological Science, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, 4Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing University of Agriculture

JoVE 59971

 Genetics
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