Viruses are tiny parasites of the living world that can only reproduce within a living being.
A virus is a submicroscopic and small microscopic agent that replicates inside the human body's living cells only. It cannot replicate alone. They are essentially made up of DNA or RNA that is surrounded by a protein coat. They use the components of a host cell and make copies of themselves. They often cause harm to these host cells in the process and eventually kill them. They also infect all life forms, from human beings to animals to plants and even bacteria and other microorganisms.
In the absence of a host cell, the viruses cannot generally function and reproduce. They cannot synthesize their proteins due to the absence of ribosomes. They cannot even store their own energy in the form of ATP ( Adenosine Triphosphate ); instead, they derive their energy from the host cells.
All viruses contain either DNA or RNA nucleic acid, and a protein coat encases the nucleic acid called the capsid. Along with this, some viruses are even covered with a coat of fats and proteins. When it is infected, a particle called the virion is present outside the cell. In some viruses, an envelope is made up of a phospholipid layer, and glycoprotein is present outside the capsid.
1. Genome or Nucleic acid: This part contains DNA or RNA. A virus that contains the DNA protein is called a DNA Virus, and that which contains RNA is called an RNA virus. For example, Reovirus is an RNA virus containing an RNA genome, and Papovavirus is a DNA virus.
2. Capsid: It is the protective protein coat. It comprises many capsomeres, which are arranged tightly together in repeating patterns. It is an impenetrable shell. Its main function is to help introduce a viral genome into the host cell during infection. The structure of a capsid is what gives symmetry to the virus. The structures can be cubical, helical, complex, or binal.
3. Envelope: Some viruses even contain an envelope surrounding the nucleocapsid. It is a layer of lipoprotein and glycoprotein, and the envelope results from the budding process from the host cell. The proteins can also project out as telomeres such as neuraminidase and haemagglutinin involved in binding virus to the host cells.
4. Enzymes: These play a central role in the infection process. For example, some viruses like bacteriophages contain enzymes like lysozyme that make a small hole in the bacterial cell that allows nucleic acid to enter.
According to Baltimore, viruses are classified into VII groups based on the method of replication, they are:
1. What are the three structures of a virus?
Based on symmetry, the three structures of a virus are Helical, Complex and Cubical structures.
2. What are the four main parts of a virus?
The four main parts of a virus are Genome, Capsid, Envelope, and Enzymes.
3. What are the five characteristics of a virus?
The 5 characteristics of a virus are:
4. What are the four shapes of viruses?
5. What best describes a virus?
A virus is an organism that is smaller than a bacterium that cannot grow or reproduce by itself but uses the host cell as an agent.
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