How are virions classified on their nucleocapsid nature?
Answers
Virus classification
Viruses are classified on the basis of morphology, chemical composition, and replication method. Viruses infecting humans are currently grouped into 21 families, which show only a small part of spectrum of various virus races, whose hosts extend from vertebra to protozoa and bacteria from plants and fungi.
Morphology
Helical symmetry
In replicating the viruses of helical symmetry, similar protein subunits (protomers) are assembled in a helical array around nucleic acid, which adhere to a similar spiral path. Such nucleocapsidos make rigid, highly expanded rods or flexible filaments; In any case, the description of the capsid structure is often explained by electron microscopy. Apart from the classification, in the form of flexible or rigid and naked or envelope, the helical nucleocapsids are characterized by the length, width, pitch of the helix, and the number of protomers per hectare point. The most widely studied helical virus is the Tobacco Mosaic Virus. X-ray diffraction studies have identified many important structural characteristics of this plant's virus. Sendai Virus, an envelope virus with helical nucleocyzed symmetry, is a member of the Paramedosvirus family.
Icosahedral symmetry
An icosahedron is a polyhedron in which there are 20 equivalent triangle faces and 12 vertex lines define the axis of five times rotational symmetry through the opposite vertease: all the structural features of polyhedron are five within the 360 degree rotation of five axis each Repeat times. Through the centers of opposite triangular faces, the lines make the axis of rotation symmetry three times; Two-fold rotating symmetry axes are formed by the lines through the midpoints of the opposite edges. An echocasheron (polyhedral or spherical) is defined as 532 symmetry (read as 5,3,2) with five times the rotation symmetry, three times, and two-fold axis.
The virus was first detected by X-ray diffraction studies for 532 symmetry and later found with electron microscopy with negative-blurred techniques. In most Icocashedral viruses, protomers, i.e. structural polypeptide chains, are arranged in the oligomeric cluster called capsomeres, which are easily portrayed by negative staining electron microscopy and form a closed capsid shell. The arrangement of capsomeres in an IcosaHedral shell allows the classification of such viruses by capsular number and pattern. For this it is necessary to identify the closest pair of vertex capsomeres (called penton: through which five times symmetry is close to the axis) and distribution of capsomerase between them.
Answer:
Viruses are small obligate intracellular parasites, which by definition contain either a RNA or DNA genome surrounded by a protective, virus-coded protein coat. Viruses may be viewed as mobile genetic elements, most probably of cellular origin and characterized by a long co-evolution of virus and host. For propagation viruses depend on specialized host cells supplying the complex metabolic and biosynthetic machinery of eukaryotic or prokaryotic cells. A complete virus particle is called a virion. The main function of the virion is to deliver its DNA or RNA genome into the host cell so that the genome can be expressed (transcribed and translated) by the host cell. The viral genome, often with associated basic proteins, is packaged inside a symmetric protein capsid. The nucleic acid-associated protein, called nucleoprotein, together with the genome, forms the nucleocapsid. In enveloped viruses, the nucleocapsid is surrounded by a lipid bilayer derived from the modified host cell membrane and studded with an outer layer of virus envelope glycoproteins.