Viruses-Introduction-History,Virus General characteristics

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Viruses Introduction

Viruses square measure still biologists’ puzzle as a result of they show each living and nonconscious characters. therefore viruses square measure thought to be a separate entity. it’;;;s not taken under consideration in Whittaker’s 5 kingdom classification. Viruses square measure currently outlined as light microscope, malady inflicting intra cellular obligate parasites.

Brief history of discovery

Viruses weren’;;;t well-known to biologists for a protracted time owing to their light microscope structure although their presence was apparent by infectious diseases that were evidenced undue to bacterium. It attracted the eye of investigators solely within the nineteenth century once a plague known as mosaic virus (TMV) caused severe harm to commercially vital tobacco crop. Mayer incontestable  that the malady may well be transmitted simply by applying the sap of infected leaf to the leaf of healthy plant. He thought that the malady was owing to a microorganism. it absolutely was then the Russian scientist Iwanowsky (1892) UN agency

demonstrated that the sap of infected leaves even once passing through microorganism filter remained infective, ruling out the microorganism because the activating agent. Dutch life scientist Beijerinck (1898) confirmed the findings of Iwanowsky and known as the fluid “contagium vivum fluidum” which implies contagious living fluid. This was shortly known as particle (poison) and also the malady inflicting agent as virus. W.M. Stanley (1935), the yankee chemist, isolated virus in crystalline kind and incontestable  that even therein state it maintained the infectivity. This marked the start of a replacement branch of science known as medicine.

General characteristics

Viruses square measure light microscope and might cause diseases in plants and animals. they’;;;re terribly easy in their structure. they’;;;re composed of supermolecule encircled by a macromolecule coat. supermolecule are often either ribonucleic acid or DNA, however ne’;;;er each. they need no cellular organization and don’;;;t have any machinery for any

metabolic activity. they’;;;re obligate intracellular  parasites and that they multiply among their host cells. Once outside the host cell they’;;;re utterly inactive.

Size and form

Viruses square measure terribly minute particles that they will be seen solely underneath microscope. they’;;;re measured in micromillimeters ( one millimicr (1micron – 1/1000 millimeter). usually they vary from a pair of.0 millimetre to three hundred millimetre in size. terribly tiny size and skill to labor under microorganism filters square measure classic attributes of viruses. the subsequent strategies square measure wont to confirm the scale of the viruses.

1. Direct observation by victimisation lepton microscope:

2. Filtration through membranes of stratified porosity: during this methodology viruses square measure created to labor under a series of membranes of well-known pore size, the approximate size of any virus are often measured by determinative that membrane permits the virus to labor under and that membrane holds it back.

3. alluviation by immoderate natural action : the connection between the scale and form of a particle and its rate of alluviation permits determination of particle size.

4. Comparative measurements: the subsequent information is employed for reference.

a. coccus features a diameter of a thousand millimetre.

b. virus varies in size from 10-100 nm. generally viruses occur in 3 main shapes:

1. cuboid symmetry:

polyhedral or spherical – eg.

Adeno virus, HIV

2. volute symmetry: e g .

Tobacco Mosaic virus

(TMV), respiratory illness virus.

3. advanced or atypical eg.

Bacteriophage, Pox virus.

Structure of a plague a plague consists of 2 major components one.Capsid (the macromolecule coat) a pair of.Nucleic acid. The capsid is that the outer macromolecule coat. it’;;;s protecting in perform. it’;;;s usually composed of the many

identical subunits known as capsomeres. a number of the viruses have associate degree outer covering known as envelope eg. HIV. they’;;;re known as engulfed viruses. Others square measure known as naked viruses or non- engulfed viruses. The

capsid is in shut contact with the supermolecule and therefore called nucleocapsid. The supermolecule forms the central core. in contrast to any living cell a plague contains either DNA or ribonucleic acid, however ne’;;;er each. The infective nature of the virus is attributed to the supermolecule whereas host specificity is attributed to the macromolecule coat.

Virion

An intact, infective virus particle that is non-replicating outside a bunch cell is termed particle. Viroids A plant virus could be a circular molecule of ss ribonucleic acid while not a capsid. Viroids cause many economically vital plant diseases, as well as Citrus exocortis. Rions (pronounced “preeons” ) they’;;;re supermolecule infectious particles. they’;;;re the activating agents for a couple of dozen fatal chronic disorders of the central nervous systems of humans and alternative animals. eg. Creutzfeldt-Jacob Disease(CJD), Bovine Spongiform {encephalopathy|brain disorder|brain malady|nervous disorder|neurological disorder|neurological disease} (BSE)-Commonly called mad cow disease, etc .They are terribly distinctive among infectious agents as a result of they contain no genetic material i.e DNA/RNA. Stanley Prusiner did most of the work on prions and was awarded laurels in 1998.

Classification of virus

Although viruses aren’;;;t classified as members of the 5 kingdoms, they’;;;re various enough to need their own classification theme to assist in their study and identification. in step with the sort of the host they infect, viruses square measure classified chiefly into the subsequent four varieties.

1. Plant viruses as well as protoctist viruses-RNA/DNA

2.Animal viruses as well as human viruses-DNA/RNA

3.Fungal viruses(Mycoviruses)-ds ribonucleic acid

4.Bacterial viruses (Bacteriophages) as well as cyanophages-DNA

1.Plant viruses

They infect plants and cause diseases. Some common plant microorganism diseases are:

a. Mosaic diseases of tobacco (TMV), cucumber (CMV), cauliflower.

b. concentrated prime of banana

c. Leaf-roll of potato

d. noticed wilt of tomato

Generally, plant viruses have ribonucleic acid with the exception of some viruses like cauliflower mosaic virus that has DNA.

2. Animal viruses

They infect animals and cause diseases. The supermolecule is either DNA or ribonucleic acid. a number of the diseases caused by viruses in groups of people are: communicable disease, measles, tiny pox ( currently extinct) chicken pox, Jaundice, herpes, hapatitis A B,C,D,E,G, influenza, polio, mumps, rabies, AIDS and severe acute respiratory syndrome. Viruses additionally cause diseases in kine. eg. Foot and mouth malady. (FMD) in kine, distemper  dog,  redness of horse, , rabbies etc.   that cause diseases in fungi square measure known as mycophages and viruses that attack blue inexperienced algae/cyanobacteria and cause diseases square measure known as cyanophages.

4. Bacteriophages

Virus that infects bacterium is termed virus or just bacteriophage. it’;;;s larva like and also the supermolecule is DNA eg. T2, T4, T6 bacteriophages.

Life cycle of a bacteriophage

Phages exhibit 2 differing types of life cycle.

1. Virulent or lytic cycle

2. Temperate or lysogenic cycle.

1. Virulent or lytic cycle

Intra cellular multiplication of the bacteriophage ends within the lysis of the host microorganism and also the unharness of relative virions. Replication of a virulent bacteriophage takes place within the following stages.

1. sorption a pair of.Penetration three.Synthesis of bacteriophage parts four.Assembly

5.Maturation vi.Release of relative bacteriophage particles

1. Adsorption

The attachment of the bacteriophage to the surface of a prone microorganism by means that of its tail is termed sorption. Host specificity of the bacteriophage is set within the sorption stage of the cycle. Artificial direct injection of bacteriophage DNA are often achieved even in strains of bacterium that aren’;;;t

susceptible to the bacteriophage. The infection of a microorganism by the naked bacteriophage supermolecule is thought as transfection.

2. Penetration

The process of penetration resembles injection through a syringe. The bacteriophage DNA is injected into the microorganism cell through the hollow core. once penetration the empty head and also the tail of the bacteriophage stay outside the microorganism because the shell.

3.Synthesis of bacteriophage parts

During this stage synthesis of microorganism macromolecule, DNA, and ribonucleic acid ceases. On the opposite hand, phage DNA, head macromolecule and tail macromolecule square measure synthesized on an individual basis within the microorganism cell. The DNA is succinctly ‘packaged’ within the solid head and at last the tail structures square measure intercalary.

 4. The assembly of bacteriophage parts into mature infectious bacteriophage particle is thought as

(5) Maturation.

6. unharness of phages

Release of phages usually takes place by the lysis of the microorganism cell. throughout the replication of phages, the microorganism cell membrane is weakened and it assumes a spherical form and at last burst or lyse. Mature female offspring phages square measure free.

Lysogenic cycle

The temperate phages enter into a dependent relationship with the host cells. there’;;;s no death or lysis of the host cells. Once within the host cell the temperate bacteriophage supermolecule becomes integrated with the microorganism ordering. currently the integrated bacteriophage supermolecule is termed a prophage. The prophage behaves sort of a section of the host body and replicates along side it. This development is termed lysogenicity. The microorganism that cavity a prophage among its ordering is termed lysogenic microorganism. The prophage confers bound new properties on the microorganism. this can be known as lysogenic conversion or bacteriophage conversion. associate degree example is poison production by the Diptheria B that is set by the presence of prophage beta.

Plant microorganism malady

Bunchy prime of banana

Banana concentrated prime virus causes this malady. The infected plant shows very inferior growth. Leaves become short and slim. Affected leaves square measure crowded  during a rosette like fashion (bunch of leaves) at the highest of the plant.Chlorosis and curling of the leaves additionally occur. unhealthy plants ought to like a shot

be uprooted and burnt to avoid any infection. rising microorganism infections( in human beings)

Recent samples of rising microorganism infections in numerous regions of the globe embrace filovirus, HIV, dengue, VHF, viral hemorrhagic fever, vale fever, SARS.

AIDS: (Acquired Immuno Deficiency Syndrome) could be a recently discovered sexually transmitted virus malady. it’;;;s caused by Human Immuno Deficiency Virus ( HIV ). HIV belongs to a gaggle of viruses known as retroviruses. It infects the T4 lymphocytes called helper cells that kind the most line of body system. HIV kills the T4 lymphocytes and also the ensuing depletion of T4 cell population creates associate degree immune deficiency. This paves manner for several opportunist pathogens to attack. AIDS by itself isn’;;;t a killer malady. it’;;;s solely the opposite opportunist pathogens that kill the infected persons.

Symptoms

HIV infection causes fever, loss of weight, persistent generalized lymph gland enlargement and opportunist infections like T.B . etc. The AIDS patients may have headache, fatigue, persistent diarrhea, dry cough, lymphomas and harm of the central systema nervosum. usually there’;;;s look of thrush within the mouth and throat and night sweats. Changes in behaviour and mental disease may occur.

Mode of infection

Primarily HIV is sexually transmitted. it’;;;s predominant among homosexuals. Persons with veneral diseases, persons UN agency have several sexual partners and prostitutes can have a lot of probabilities of HIV infection. the most typical methodology of transmission is thru sexual activity with several persons.

The other strategies of transmission square measure throughout intromission, tissue or organ donation of HIV

infected persons to healthy persons, injections with unsterilised syringes and needles and shared needles

by drug addicts. AIDS will unfold from infected mother to the kid throughout gestation or through infant feeding.

Prevention

Since there’;;;s no cure for AIDS the simplest approach to manage AIDS is bar. Reduction of sexual sexual practice and adoptions of prophylactic measures (such because the use of condoms) will cut back  transmission through sexual activity. Transmission through the shared needles by drug addicts is also reduced by correct education. The transmission through intromission is also eliminated by correct

serological screening of given blood for the presence of HIV antibodies. Transmission from infected mother to kid are often reduced by preventing or terminating gestation. medication like ZDV  azidothymidine) solely facilitate to extend the lifetime of the victim by few a months and don’;;;t provide complete cure for the

disease.

Viruses and cancer

Cancer is associate degree uncontrollable and unorganized growth of cells inflicting malignant neoplasm. The cells of this tumours have the capability to unfold indiscriminately anyplace within the body. In recent years, there has been increasing proof to prove that the cancer is caused by the DNA virus known as Simian virus (SV-40) and a gaggle of ribonucleic acid viruses known as retroviruses. The cancer inflicting viruses are known as oncogenic viruses. it’;;;s currently believed that some viruses square measure concerned in leukaemia, malignant neoplastic disease and a few quite

breast cancer additionally.

A new malady known as severe acute respiratory syndrome

Severe Acute metabolic process

Syndrome (SARS) could be a respiratory disease that has recently been rumored in South East Asia, North America and Europe. it’;;;s created panic among the individuals everywhere the globe and has resulted in nice

economic loss for several countries like China, Singapore etc.

Symptoms

It begins with high fever. alternative symptoms embrace headache, discomfort and body aches. Patient might develop dry cough and have bother in respiratory.

How severe acute respiratory syndrome unfold

It seems to unfold by person to person contact particularly with infectious material (for example metabolic process secretions.) The viruses that cause severe acute respiratory syndrome square measure perpetually ever-changing their kind which is able to

make developing a immunizing agent troublesome. severe acute respiratory syndrome is caused by a gaggle of viruses known as corona viruses that square measure engulfed viruses. Their ordering is single stranded ribonucleic acid. The nucleocapsid is volute. These viruses have flower petal formed surface projections organized during a fringe sort of a star corona.

Viral vaccines

The purpose of microorganism immunizing agent is to utilize the reaction of the host to forestall microorganism diseases. Vaccination is that the most price effective methodology of bar of great virus infection.

Interferons (IFNs)

They are the host coded proteins of protein family that inhibit microorganism replication. they’;;;re created by intact animal or civilised cells in response to virus infection or alternative inducers. they’;;;re believed to be the a part of body’s 1st line of defense against virus infection.

Significance of Viruses

1. Viruses square measure a form of biological puzzle to biologists since they’;;;re at the threshhold of living and non-living things showing the characteristics of each.

 2. Viruses square measure considerably used as research project tools owing to their simplicity of structure and speedy multiplication. they’;;;re wide employed in analysis

especially within the field of biology, recombinant DNA technology, drugs etc.

 3. Viruses square measure employed in eradicating harmful pests like insects. so they’;;;re employed in Biological management Programmes.

4. Plant Viruses cause nice concern to agriculturists by their unhealthful nature. Bacteriophages attack the N2 fixing bacterium of soil and square measure liable for reducing the fertility of soil. 5. In trade, viruses square measure employed in preparation of sera and vaccines.

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