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What are the 3 types viruses? What is the body's main defense against viruses? Study Guides. Trending Questions. What's the most outdated thing you still use today? Is it better to take a shower in the morning or at night?

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What Latino American psychologists studies showed cultural bias on intelligence tests? What do you call a rattle snake on a cold and blustery day? Get the Answers App. Viruses are inert outside the host cell. Small viruses, e. Viruses are unable to generate energy. As obligate intracellular parasites, during replication, they fully depend on the complicated biochemical machinery of eukaryotic or prokaryotic cells. The main purpose of a virus is to deliver its genome into the host cell to allow its expression transcription and translation by the host cell.

A fully assembled infectious virus is called a virion. The simplest virions consist of two basic components: nucleic acid single- or double-stranded RNA or DNA and a protein coat, the capsid, which functions as a shell to protect the viral genome from nucleases and which during infection attaches the virion to specific receptors exposed on the prospective host cell. Capsid proteins are coded for by the virus genome. Because of its limited size Table the genome codes for only a few structural proteins besides non-structural regulatory proteins involved in virus replication.

Capsids are formed as single or double protein shells and consist of only one or a few structural protein species. Therefore, multiple protein copies must self assemble to form the continuous three-dimensional capsid structure.

Self assembly of virus capsids follows two basic patterns: helical symmetry, in which the protein subunits and the nucleic acid are arranged in a helix, and icosahedral symmetry, in which the protein subunits assemble into a symmetric shell that covers the nucleic acid-containing core.

Some virus families have an additional covering, called the envelope, which is usually derived in part from modified host cell membranes. Viral envelopes consist of a lipid bilayer that closely surrounds a shell of virus-encoded membrane-associated proteins.

The exterior of the bilayer is studded with virus-coded, glycosylated trans- membrane proteins. Therefore, enveloped viruses often exhibit a fringe of glycoprotein spikes or knobs, also called peplomers.

In viruses that acquire their envelope by budding through the plasma or another intracellular cell membrane, the lipid composition of the viral envelope closely reflects that of the particular host membrane. The outer capsid and the envelope proteins of viruses are glycosylated and important in determining the host range and antigenic composition of the virion.

In addition to virus-specified envelope proteins, budding viruses carry also certain host cell proteins as integral constituents of the viral envelope. Virus envelopes can be considered an additional protective coat. Larger viruses often have a complex architecture consisting of both helical and isometric symmetries confined to different structural components.

Viruses are classified on the basis of morphology, chemical composition, and mode of replication. The viruses that infect humans are currently grouped into 21 families, reflecting only a small part of the spectrum of the multitude of different viruses whose host ranges extend from vertebrates to protozoa and from plants and fungi to bacteria. In the replication of viruses with helical symmetry, identical protein subunits protomers self-assemble into a helical array surrounding the nucleic acid, which follows a similar spiral path.

Such nucleocapsids form rigid, highly elongated rods or flexible filaments; in either case, details of the capsid structure are often discernible by electron microscopy. In addition to classification as flexible or rigid and as naked or enveloped, helical nucleocapsids are characterized by length, width, pitch of the helix, and number of protomers per helical turn.

The most extensively studied helical virus is tobacco mosaic virus Fig. Many important structural features of this plant virus have been detected by x-ray diffraction studies. Figure shows Sendai virus, an enveloped virus with helical nucleocapsid symmetry, a member of the paramyxovirus family see Ch.

The helical structure of the rigid tobacco mosaic virus rod. About 5 percent of the length of the virion is depicted. Individual 17,Da protein subunits protomers assemble in a helix with an axial repeat of 6. Each more Fragments of flexible helical nucleocapsids NC of Sendai virus, a paramyxovirus, are seen either within the protective envelope E or free, after rupture of the envelope.

The intact nucleocapsid is about 1, nm long and 17 nm in diameter; its pitch more An icosahedron is a polyhedron having 20 equilateral triangular faces and 12 vertices Fig. Lines through the centers of opposite triangular faces form axes of threefold rotational symmetry; twofold rotational symmetry axes are formed by lines through midpoints of opposite edges.

An icosaheron polyhedral or spherical with fivefold, threefold, and twofold axes of rotational symmetry Fig. Icosahedral models seen, left to right, on fivefold, threefold, and twofold axes of rotational symmetry. These axes are perpendicular to the plane of the page and pass through the centers of each figure. Both polyhedral upper and spherical lower forms more Viruses were first found to have symmetry by x-ray diffraction studies and subsequently by electron microscopy with negative-staining techniques.

In most icosahedral viruses, the protomers, i. The arrangement of capsomeres into an icosahedral shell compare Fig. This requires the identification of the nearest pair of vertex capsomeres called penton: those through which the fivefold symmetry axes pass and the distribution of capsomeres between them.

Helical viruses consist of nucleic acid surrounded by a hollow protein cylinder or capsid and possessing a helical structure. Polyhedral viruses consist of nucleic acid surrounded by a polyhedral many-sided shell or capsid, usually in the form of an icosahedron.

Enveloped viruses consist of nucleic acid surrounded by either a helical or polyhedral core and covered by an envelope. Binal complex viruses have neither helical nor polyhedral forms, have irregular shapes, or have complex structures.

Contributors and Attributions Dr. Nursing researchers have also benefited HIV testing and prevention in Malawi via identifying the benefits of working with religious leaders to promote HIV testing and prevention behaviors. Additionally, nurses have developed family planning services in Kenya by providing childbearing families with the opportunity to space pregnancies to support the health of pregnant women.

Advanced practice nurses are uniquely qualified to conduct research and assist government leaders and public health officials in creating an informed response to viral outbreaks. The input and insight of experienced nurses will help prevent the spread of infectious diseases and ensure a healthier future.

Our innovative way of thinking makes us adaptable, but our focus on education makes us formidable. Skip to main content. Types of Viruses and How They Work Over many centuries and even millennia, infectious diseases such as smallpox and measles have claimed millions of lives. The Cost of Deadly Virus Infections Viruses gain their infamy through a combination of large infection rates and death, even when their power has been relatively subdued.

The Three Categories of Viruses There are three different virus types that are made distinct by their shape. How a Virus Spreads The first thing a virion does is enter a cell and becomes a virus. Treating Viruses Antiviral drugs can treat viruses by inhibiting viral development and slowing down disease progression. The Role of Advanced Practice Nurses Worldwide Around the world, nurses contribute to the prevention, management and containment of viral outbreaks by caring for infected patients and educating the public on prevention strategies.

The Invaluable Contribution of Nurses Across a variety of roles and specializations, nursing professionals fight viruses in numerous ways. Slowing the Spread Advanced practice nurses are uniquely qualified to conduct research and assist government leaders and public health officials in creating an informed response to viral outbreaks.