Biology notes on viruses essay

In it the viruses are cylindrical or rod like and the capsomeres are arranged in spiral manner around the long axis.

Virus biology discussion

The cultures of cell obtained so are called diploid cell strain. Figure The steps in the lytic replication cycle of an enveloped virus are illustrated for rabies virus, which has a single-stranded RNA genome. Virions, single virus particles, are very small, about 20— nanometers in diameter. He considered that taxa were best derived by considering all available characters and equal weight to each. Because of the extensive use of viruses in cell biology research and their potential as therapeutic agents, we describe the basic aspects of viral structure and function in this section. They can infect healthy plants just like bacteria and fungi. See Article History Alternative Title: Virales Virus, an infectious agent of small size and simple composition that can multiply only in living cells of animals , plants , or bacteria. Rabies or Rhodoxin are bullet shaped Fig. The site of administration varies according to the type of virus. Cultivation of Viruses: As the viruses do not reproduce independent of living host cells, they cannot be cultured in the same as bacteria and eukaryotic microorganisms. Bacteriophages and plant viruses also can be classified in this way, but the system has been used most widely in animal virology because representatives of all six classes have been identified. More recently, molecular analysis of viral replicative cycles has further refined their classification.

They can be inactivated by chemotherapy and thermotherapy. An interesting feature of viral complexity is that host and virion complexity are uncorrelated. Viral Capsids Are Regular Arrays of One or a Few Types of Protein The nucleic acid of a virion is enclosed within a protein coat, or capsidcomposed of multiple copies of one protein or a few different proteins, each of which is encoded by a single viral gene.

Biology notes on viruses essay

Tournier in Virus classification by capsid structure: Viruses can also be classified by the design of their capsids which are classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex. These newly produced virus particles virions infect the adjacent cells. In , Wendell Stanley purified and partly crystallized tobacco mosaic virus TMV ; other plant viruses were crystallized soon thereafter. The bacteria rickettsia and chlamydia are living cells that, like viruses, can reproduce only inside host cells. Only this genus has a neuraminidase activity which is on the same protein HN as the hemagglutination activity. Some plant viruses can be transmitted only if a diseased part is grafted onto a healthy plant. The components of simple viruses such as TMV, which consists of a single RNA molecule and one protein species, undergo self-assembly if they are mixed in solution. Glycoproteins and glycolipids are the major carbohydrate constituents of enveloped viruses.

Plant viruses with helical symmetry usually appear rod-shaped in electron micrographs. They are obligatory inter-cellular parasites as they are completely inactive outside the host.

Classification of viruses

Clearly, any attempt to classify viruses on the basis of the symptoms they produce or their hosts obscures many important differences in their structures and life cycles. In the latter case, proteins expressed from the viral DNA bind a specific sequence on the circular viral DNA to a similar specific sequence on the circular bacterial DNA. A significant advance was made by the American scientists John Enders , Thomas Weller , and Frederick Robbins , who in developed the technique of culturing cells on glass surfaces; cells could then be infected with the viruses that cause polio poliovirus and other diseases. Electron microscopic counting method often works well with concentrated preparations of viruses of known morphology. The method is laborious and has not been much used recently. Few viruses have more complex structure outside the nucleocapsid called envelop. Adenovirus, a non-enveloped animal virus that causes respiratory illnesses in humans, uses glycoprotein spikes protruding from its capsomeres to attach to host cells. Structural models of several virions are shown in Figure Many viruses can bind to the surface of red blood cells RBCs Fig. Viruses can also be classified by the design of their capsids. They give following arguments in support of the molecular concept: i Size of the some viruses falls within the range of sizes of protein and nucleic acid molecules, ii Building up of the viral protein monomers and of the protein coats of viruses from protein monomers follow the same general principles of chemistry as in the synthesis of protein molecules, iii Chemical and physical homogeneity of virus particles compares with the homogeneity of protein molecules, and iv Crystallization is a physical phenomenon based on the formation of configurations of minimum energy level.

Assay of Viruses: Reasons: Assay of viruses, the accurate determination of concentration, is a basic and primary pre-requisite for many reasons which are the followings: 1. Virus capsids can be classified as naked icosahedral, enveloped icosahedral, enveloped helical, naked helical, and complex.

virus structure diagram

The progress made in the physics of crystals that could be studied by X-ray diffraction provided the high resolution required to discover the basic structure of minute viruses. Many viruses attach to their host cells to facilitate penetration of the cell membrane, allowing their replication inside the cell.

are viruses alive

Animal viruses, such as HIV, are frequently enveloped. This is a logical system known as LHT system, in which divisions are made as to relative importance of different properties which are then used to place a taxon in a particular phylum, order, family, genus etc. The development of bacterial resistance to antibiotics has renewed interest in the therapeutic use of bacteriophages.

What is virus in biology

Essay 6. Since they are able to reproduce inside the host cells they can be said as living. The type of genetic material DNA or RNA and its structure single- or double-stranded, linear or circular, and segmented or non-segmented are used to classify the virus core structures. Such virions are called enveloped viruses in which nucleocapsid is enclosed in a membrane. These are solutions of salts of heavy metals, such as tungsten , that scatter the electrons from regions covered with the stain. The nucleic acid may be single- or double-stranded. They can be sedimented like proteins. Figure Structure of picornaviruses. They are transmissible from diseased to healthy hosts. Viruses differ from other living organisms: According to Lwoff and Tournier the following characteristics separate viruses from other living agents: 1 One type of nucleic acid either DNA or RNA is present in virion other agents possess both types nucleic acid. At the end of incubation period, the animals are slaughtered and washed thoroughly and viruses are obtained from them. Figure Electron micrograph of a T4 bacteriophage adsorbed onto an E. Adsorption and release of enveloped animal viruses are somewhat more complicated processes. Transmission electron micrograph of viruses: Transmission electron micrographs of various viruses show their structures.

Viruses can be concentrated by centrifugation before counting if the virus preparation is too dilute.

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Viral Evolution, Morphology, and Classification