The structure of a virus

It is a single-stranded RNA virus and has a string of nucleoproteins that helps in replication of the viral genome. It has spikes on the surface of the enveloped virus and gives a crown-like appearance under a microscope. These spikes help viruses to attach to the host cell. Some viruses are composed of several separate capsomeres with separate shape and symmetry forming complex symmetry.

They neither have icosahedral nor helical symmetry due to the complexity of their capsid structure. Examples include Poxvirus, Bacteriophage, etc. Bacteriophage is known to be the most complicated virus in terms of structure. It possesses an icosahedral head and helical tail. Such a structure is called binal symmetry. Bacteriophage is the virus that infects bacteria, these are of different types. Attempt Mock Tests.

Viruses are intracellular, obligate parasites that are on the borderline of living and non-living. They contain only nucleic acid and proteins enclosed in capsid. Viruses attach themselves to the host cell, cause incisions and insert their genome into the host body. Viruses use host cell proteins and enzymes to replicate their own genome. These genomes are packed with protein capsids and ready to spread infections to other organisms. What is the shape and structure of a virus? Ans: The shape of the virus varies due to the structure of its capsid.

The capsid can be filamentous or rod-shaped, isometric or icosahedral, spherical or complex with an icosahedral head and helical tail. What is the chemical structure of viruses?

Ans: The centre portion of the virus consists of a single molecule of nucleic acids either DNA or RNA that is surrounded by capsids made of protein units called capsomers. Some viruses also contain certain enzymes of their own. What are the three vital structures of viruses? Ans: There are mainly three types of symmetry observed in viruses that resemble two primary shapes that are rod-shaped and spherical shaped. Why are viruses considered to be on the borderline between living and nonliving?

Ans: Unlike any cellular organisms, viruses do not have any cellular nature and can be crystallised, which is a nonliving character.

On the other hand, they can multiply using host machinery inside any host cell, which is a living character. That is why viruses are considered to be on the borderline between living and nonliving. What structure is unique to a virus? Ans: Bacteriophage is known to be the most complicated or unique virus in terms of structure. We hope this detailed article on Structure of Viruses helps you in your preparation. If you get stuck do let us know in the comments section below and we will get back to you at the earliest.

Support: support embibe. General: info embibe. The same techniques were also employed in the study of complex bacteriophages that were too large to crystallize. Nevertheless, there still remained many pleomorphic, highly pathogenic viruses that lacked the icosahedral symmetry and homogeneity that had made the earlier structural investigations possible. Currently some of these viruses are starting to be studied by combining X-ray crystallography with cryo-electron tomography. Abstract This review is a partially personal account of the discovery of virus structure and its implication for virus function.

Gov't Research Support, U. Gov't, Non-P. Although viruses have been speculated as being a form of protolife, their inability to survive without living organisms makes it highly unlikely that they preceded cellular life during the Earth's early evolution. Some scientists speculate that viruses started as rogue segments of genetic code that adapted to a parasitic existence. All viruses contain nucleic acid, either DNA or RNA but not both , and a protein coat, which encases the nucleic acid.

Some viruses are also enclosed by an envelope of fat and protein molecules. In its infective form, outside the cell, a virus particle is called a virion. Each virion contains at least one unique protein synthesized by specific genes in its nucleic acid. Viroids meaning "viruslike" are disease-causing organisms that contain only nucleic acid and have no structural proteins.

Other viruslike particles called prions are composed primarily of a protein tightly integrated with a small nucleic acid molecule. Viruses are generally classified by the organisms they infect, animals, plants, or bacteria. Since viruses cannot penetrate plant cell walls, virtually all plant viruses are transmitted by insects or other organisms that feed on plants.

Certain bacterial viruses, such as the T4 bacteriophage, have evolved an elaborate process of infection. The virus has a "tail" which it attaches to the bacterium surface by means of proteinaceous "pins. Viruses are further classified into families and genera based on three structural considerations: 1 the type and size of their nucleic acid, 2 the size and shape of the capsid, and 3 whether they have a lipid envelope surrounding the nucleocapsid the capsid enclosed nucleic acid.

There are predominantly two kinds of shapes found amongst viruses: rods, or filaments, and spheres. The rod shape is due to the linear array of the nucleic acid and the protein subunits making up the capsid. The sphere shape is actually a sided polygon icosahedron. The nature of viruses wasn't understood until the twentieth century, but their effects had been observed for centuries.

British physician Edward Jenner even discovered the principle of inoculation in the late eighteenth century, after he observed that people who contracted the mild cowpox disease were generally immune to the deadlier smallpox disease.

By the late nineteenth century, scientists knew that some agent was causing a disease of tobacco plants, but would not grow on an artificial medium like bacteria and was too small to be seen through a light microscope.

Advances in live cell culture and microscopy in the twentieth century eventually allowed scientists to identify viruses. Advances in genetics dramatically improved the identification process.

Capsid - The capsid is the protein shell that encloses the nucleic acid; with its enclosed nucleic acid, it is called the nucleocapsid. This shell is composed of protein organized in subunits known as capsomers. They are closely associated with the nucleic acid and reflect its configuration, either a rod-shaped helix or a polygon-shaped sphere. The capsid has three functions: 1 it protects the nucleic acid from digestion by enzymes, 2 contains special sites on its surface that allow the virion to attach to a host cell, and 3 provides proteins that enable the virion to penetrate the host cell membrane and, in some cases, to inject the infectious nucleic acid into the cell's cytoplasm.