Virus Cell Structure
Virus Cell Structure
A virus is a tiny, infectious particle that can reproduce only by infecting a host cell. Viruses are much smaller than bacteria and consist of a single- or double-stranded nucleic acid (DNA or RNA) surrounded by a protein shell called a capsid. Some viruses also have an outer envelope composed of lipids and proteins.
Key Components of a Virus
1. Nucleic Acid Genome: A virus is made up of a DNA or RNA genome. This genome is the genetic material of the virus and contains the information needed for the virus to replicate.
2. Protein Capsid: The genome is enclosed within a protective protein coat called a capsid. The capsid is made from proteins that are encoded by viral genes within their genome. The shape of the capsid may vary from one type of virus to another.
3. Lipid Envelope: Many animal viruses also contain a lipid envelope. The envelope is made from portions of the host’s cell membrane. It surrounds the capsid and helps protect the virus from the host’s immune system. The envelope may also have receptor molecules that can bind with host cells, making it easier for the virus to infect the cells.
Types of Viruses Based on Structure
1. Helical Viruses: Helical capsids are made up of a single type of protein subunit stacked around a central axis to form a helical structure. This arrangement results in rod-shaped or filamentous virions. An example of a helical virus is the tobacco mosaic virus.
2. Icosahedral Viruses: Icosahedral capsid symmetry gives viruses a spherical appearance at low magnification, but the protein subunits are actually arranged in a regular geometrical pattern. They are not truly spherical.
Virus Reproduction
Viruses reproduce by infecting their host cells and reprogramming them to become virus-making “factories”. They “commandeer” the host cell and use its resources to make more viruses.
Conclusion
Viruses are unique entities that straddle the line between living and non-l