What is Virus? It will be outlined as non-cellular infectious entities that contain ribonucleic acid or DNA sheathed in supermolecule coat and reproduce solely in a living cell. The word VIRUS comes from Latin word venome means that substance was wont to describe any disease-causing substance.
About fifty years before the development of the microscope, the existence of viruses was incontestable as an outsized cluster of one-celled disease-causing agents composed of macromolecule encapsulated in an exceedingly super molecule coat, by L. life scientist in 1884 and A. Mayer in 1886 throughout their studies on the mosaic sickness of tobacco plants. They exhibited that the sickness will be transmitted from one host to a different underneath controlled laboratory conditions. However, the character of viruses wasn’t clearly established by their experiments as a result of neither of those viruses can be full-grown in pure culture by the strategies obtainable at that point.
In 1892, D. Iwanowsky ready associate extract from tobacco plants that were laid low with mosaic sickness. once the extract was undergone a filterable to forestall the passage of bacterium, the filtrate was able to infect healthy tobacco leaves. As a result of this experiment, these disease-causing agents were named filterable viruses. In 1898 M. Beijernick established that viruses possess the property of replication that’s common to all or any living things. He any established that these disease-causing filterable viruses multiply within the host cells.
Later F. Twort and F. d’Hérelle severally discovered that some viruses infect bacterium. They termed these viruses bacteriophages, i. e. , eaters of a bacterium, or just bacteriophages. This discovery established the actual fact that viruses infect and cause diseases altogether the 3 major biological teams, the animals, plants and bacterium.
In 1935, W. Stanley incontestible the structure of virus tobacco mosaic virus. He crystallized the virus so showed that it’s mostly composed of supermolecule. Later, alternative scientists showed that these crystals additionally contain a tiny low however constant quantity of ribonucleic acid. Chemical studies of alternative viruses unconcealed that some contain DNA additionally to supermolecule, however, no virus has been found to contain each DNA and ribonucleic acid. additionally to a macromolecule, some viruses contain lipoid, and a few contain tiny amounts of carbohydrates conjugated to their supermolecule parts. the biggest and most advanced viruses, the poxviruses, area unit composed of a macromolecule and a number of other internal compartments encircled by membranes.
CHARACTERISTICS OF VIRUS
The chief characteristics of viruses they’re sickness inflicting agent. ii. they’re quite tiny, thus invisible within the microscope and able to through filters that retain most bacterium. They are doing not multiply in cultures designed to support the growth of the bacterium.
- They’re composed of macromolecule DNA or ribonucleic acid core encircled and by a supermolecule coat known as capsid.
- The DNA or ribonucleic acid functions as infective agent order. those who contain ribonucleic acid contain associate uncommon biological property of getting genetic data for good.
TYPES OF VIRUSES
Generally the viruses will be divided into the subsequent types:
- Animal Viruses:
These cause diseases in man and alternative animals. they sometimes carries with it DNA core protected by capsid.
- Plant Viruses:
These cause diseases in plants. A virus consists of ribonucleic acid core encircled by protecting supermolecule coat. for instance mosaic virus (TMV).
This is a special cluster of viruses. they need ribonucleic acid as their genetic material. They cause serious sickness like AIDS in humans.
These area unit plant viruses that contain fiber DNA as genetic material.
MORPHOLOGY OF VIRUSES
Size and form of Viruses
Viruses vary greatly in size and form. the tiniest, simplest and structurally complete infectious viruses area unit virions.
These home in size from twenty to 350 nm. Most viruses home in size between ten and three hundred nanometers. polio, yellow-fever and foot-and-mouth disease-causing viruses area unit smaller in size with a diameter of regarding twenty five nm, whereas pox viruses area unit larger, regarding 250 nm in diameter. Since most viruses live but one hundred fifty nm, thus they’re visible solely underneath microscope.
The viruses exhibit a range of shapes. they will be rod-like, i. e., elongated sort of a piece of insulated line (TMV); rounded (mump virus, animal virus, respiratory disorder virus); tadpole-shaped (bacteriophages); or bullet-shaped (rabies virus). Bacteriophages exist in numerous shapes, however, most of them possess a solid head and a tail through that they infect the host cell. Some bacteriophages area unit threadlike.
Generalized Structure of an epidemic
The viruses area unit non-cellular and possess a really straightforward structure. every virus consists of a DNA or ribonucleic acid filament forming a core. The absolutely assembled, an infective particle is termed a particle.
The virus DNA is encircled by a coat of supermolecule known as a capsid. This structure shaped macromolecule and capsid is mostly termed nucleocapsid. The capsid is formed from proteins. These embody basic proteins, the histones; histone-like proteins (adenoviruses); or tiny peptides and polyamines (bacteriophages). Lipids and carbohydrates also are found in viruses. These embody phospholipids, glycolipids, neutral fats, fatty acids, and cholesterin. lipide is predominant in infective agent envelope.
The virus coats (capsids) area unit typically designed from identical continuation units known as capsomeres. The capsomeres kind extremely symmetrical structures which will be crystallized and facilitate to check their structure through X-ray physical science and microscopy. Most animal viruses like herpes and respiratory disorder viruses have an extra conjugated protein envelope derived from the surface membrane of the host cell. However, all the plant viruses and bacteriophages area unit naked.
The infective agent order consists of nucleic acids. Bacteriophages and animal viruses contain DNA whereas plant viruses contain ribonucleic acid sometimes. each DNA and ribonucleic acid ne’er exist within the same particle. A virus that contain solely one copy of the macromolecule area unit known as haploid. However, retroviruses area unit contains 2 identical ribonucleic acid single strands. in order that they area unit termed diploid.