Variety of life Or Virology

 The study of viruses is called virology.  It is a non-cellular infectious entity that contains only nucleic acids and proteins. 

• The viruses utilize the biosynthetic machinery of the host for their own synthesis.
• Charile has filterated the agents which are responsible for rabies, while bacteria cannot pass through these porcelain filters. Lavanisko discovered the Tabacoo Mosaic virus
• These viruses were purified by Stanely successfully by crystalizing these agents. (TMV). T  Twort discovered the virus which infects and kills the bacteria as he discovered that the bacterial cell colony undergoes lysis and this process transfer from one colony to another colony. D Herle also discovered the same phenomena and named them "Bacteriophage".
• Davin Baltmore got the noble prize as he divided  the virus into seven groups depending upon their mode of replication and genome. 

Viruses have the simplest chemical compositions.  These are visible under an electron microscope only.  The largest virus has a range of 250nm called poxvirus and the samllest virus has range of 20nm called parvovirus and are 10 to 1000 times smaller than that of bacteria. These cannot be grown on artificial media.  Therefore these are called obligate intracellular parasites. The viruses have resistant to a broad range of antibiotics.

Structure of Virus:

               The virus has the central core and the outer capsid. The central core is made up of the nucleic acid which is either DNA or RNA and the capsid is made up of protein subunits called capsomeres.

•  Adenoivirus that cause cold has 252 capsomerse in its capsid.
• The herpes virus has 162 capsomers in its capsid.
• Polio virus has 32 capsomere in its capsid.
• Some viruses have envelope outer to its capsid which is derived from the host cell and made up of lipoprotein.
• Some viruses have a spikes which are used for the recognitation of the cells and are made up of glycoproteins.
• Viruses also have no fossil records.

Classification of Viruses:

• based on their structure and shape, these are divided into three forms:

1. Rod-shaped virus( TMV)
2. Shepherical virus( Poliovirus)
3. Tadpole virus( Bacteriophage)

• based on capsid:

1.  Helical capsid(TMV)
2. Polyhedral virus(Adenovirus)
3. Enveloped virus(Influenza virus )
4. complex capsid virus(Bacteriophage) 

• based on the genome:

1. Double standard DNA(ds DNA) virus(Smallpox, adenovirus, herpes virus)
2. Single standard DNA (ss DNA) virus(parvovirus cause midrash)
3. ds RNA Virus ( Reovirus, diarrhea virus)
4. ss RNA Virus ( HIV, Rubella virus, and Influenza virus(orthoremyxovirus))

Enveloped Viruses:   Small pox virus( enveloped DNA ), HCV   ,influenza virus, Paramoxyoviruses( Enveloped RNA virus)

HAV is an RNA non-enveloped virus.

Most Plant viruses contain only RNA  and these viruses have more ability to mutate than DNA viruses. 200 viruses cause some cold and are called cold viruses. 

2000 types of plant viral diseases have been discovered still. Rous sarcoma virus causes cancer in animals. Papovirus causes warts. Picornovirus causes hepatitis A, Polio. ( The smallest known RNA non-enveloped virus is called poliovirus or enterovirus). Every virus can attack its specific host and not all living organisms.

• All the hepatitis viruses infect only liver cells.
• HIV or AIDS virus infects only WBC, especially T- Helper lymphocytes, macrophages, and certain types of brain cells (CNS).
•  Cold viruses infect only the cells of tracts of the respiratory systems.
• The Poliovirus which is the smallest known virus can infect only spinal nerve cells.
• The Rabies virus can not infect all animals but only mammals.
• Bacteriophage virus infects only the bacteria cells.

RETROVIRUS:

The RNA encompassed infection which is round in structure, and are answerable for growth creation in living cells are called retrovirus. These are likewise called oncovirus as they cause disease. A portion of these infection are vague in its activity yet by and large retrovirus are have explicit. For instance, HIV infection which cause cold.

HIV:

    It is an RNA-encompassed infection that is round in shape. The envelope which is lipoproteins in nature

furthermore, comprises of two layers. The external film is the glycoprotein layer (gp120) and it is fundamental for the connection to the host cell. while the internal layer is the transmembrane (gp41) and it is fundamental for the cell combination process. Between the envelope and the capsid, there is the framework of proteins.

The HIV capsid is tapered in shape and is made out of capsomers. This capsid contains two strands of ssRNA and The chemicals required for replication e.g.: Turn around transcriptase, protease, and intergrase.

life cycle:

      The intial step of HIV is the landing or the attachment on the host cell. It is characterized by the binding of the  gp120 to the Cd4 receptors of cells which are also glycoprotein in nature. The next step is the fusion of the viral cell with the host cell and then the viral RNA and viral enzymes are realsed into the host cells. The enzyme reverse transcriptase uses the viral RNA as a template and synthesizes complementary single standard DNA. After this, the viral RNA is disintegrated by the ribonuclease enzyme. This cDNA synthesizes another DNA strand and forms double standard DNA which is integrated into the host cell chromosome by integrase and now this integrated DNA is called a provirus. A viral mRNA is synthesized from this DNA and also genomic RNA is produced. These viral mRNAs are translated by host ribosomes for the synthesis of large proteins which are broken by an enzyme called protease into structural proteins. The viral components are then assembled and the complete and mature virion is budded off by taking the portion of the host membrane and in this way the host cell becomes dysfunctional. 

  AIDs itself is not a disease but it destroys the immune system and in this way, the immunity against other diseases is reduced and attacked by normal diseases called opportunistic .These diseases include: eye infection, cancer, viral and fungal infection and serval nervous diseases.

AIDS is a disease for which the vaccine is still not available.  The main causes for its spreading are of using contaminated syringes, contaminated scissors and increasing your sexual relationship. So by avoiding these activities, you can be safe from AIDs.