The viruses are a set of genes, either deoxyribonuclei acid (DNA) or Ribonucleic acid (RNA), packed in a coated protein. Viruses that infect humans are considered as animal viruses’. The dangerous in a way that, they also infect other microorganisms like bacteria. Viruses that infect bacteria are refereed to as phages. There are considered as intracellular parasites, they can only survive inside a living cell.
Viruses enter and infect cells and program their cellular machinery to synthesize and produce their own viral constituents call virions. The infected host cell may now divide and produced thousands of new virions and that the host cell dies. Cell death result in tissue damages which account for pathology of many viral diseases in humans. In most of the cases, the host infected cells survive, resulting in persistent viruses’ production and as results a chronic infection may remain asymptomatic, producing a chronic disease state or leading to a relapsing of an infection.
In some instances, viruses’ fails to multiply and reproduce itself and instead enters a dormant or latent states. This only happens if the virus has integrated into host cell genomes. Of which, there is a potential for reactivation at a later stage. A possible results of the presence of viral genes in a latent state is a new genotype for the cell. The formation of new genotypes are the reasons why viral infection leading to a disease, hard to treat or eliminates. Some malignancies, cancer associated of human cells are good examples of genetic effects of latent viruses’.
In the discussion to follow, the microbiology and molecular biology, genetic bases of this phenomenon are provided. Three themes are emphasized: 1. Different viruses’ can have very different structures, 2. Because of the viruses’ small size genetic built, viruses’ achieve a very high degree. 3. Although viruses’ depends on the host cell functions, therefore, are very difficult to treat or clear medically. But they have unique steps in their replication cycles, which are targeted by antiviral therapy.
Size of viruses and design
Viruses are approximately 100 – 1000 folds s!mallerr than the cell they infect. The smallest viruses such as parvoviruses, are ranging from 20 – 30 nm in diameters. Whereas the largest animal viruses such as poxviruses, overlap the size of the smallest bacterial cells which are Chlamydia and Mycoplasma, with a diameter of approximately 300 nm. In short, viruses can generally pass through filters designed to trap bacteria, and this property can as evidence of a viral etiology.
The basic design of all true viruses places the nucleic genome on the inside of a protein shell called a capsid. Some human viruses are furthermore packed into a lipid membrane, or envelope, which is usually acquired from the cytoplasmic membrane of the infected cell during egress from the cell. Viruses that are not enveloped have a defined external capsid and are referred to as naked capsid viruses.
Enveloped viruses contain a nucleic acid-protein complex called a nucleocapsid surrounded by a matrix proteins that serves as a bridge between the nucleocapsid and the inside of the membrane envelope. The protein shell forming the capsid or the nucleocapsid assumes one of two basic shapes, cylindrical or spherical. The outer shell of viruses functions 1. To protect the nucleic acid genome from damage during the extracellular passage of the virus from one cell to another, 2. To aid in the process of entry into the cell, and 3. To package enzymes essential for the early steps of the infection process.
Generally, the length of the viral nucleic acid genome is hundreds of times the longest dimension of the complete virion. The viral genome must be extensively condensed during the process of virion Assembly. For naked capsid viruses, this condensation is achieved by the association of the nucleic acid with basic protein to form what is called the core of the virus.
The core proteins are encoded by the virus, but DNA-containing animal viruses, the basic proteins are his tones scavenged from the host cell. For enveloped viruses, the formation of the nucleocapsid serves to condense the nucleic acid genome.
Classes of viral infectious agents
Two classes of infectious agents exist that are structurally simpler than viruses. Viroids are infectious circular RNA molecules that lack protein shells, they are responsible for a variety of plant diseases. Prions, which apparently lack any genes and are composed only of protein, furthermore are agents that appear to be responsible for some chronic severe neurologic diseases such as scrapie in sheep and Creutzfeldt-Jakob syndrome in humans.
Check Genomic structures: viruses causing infection and diseases for continuation from this page.