What are viruses and their structure?

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viruses are a unique group of pathogens with a simple cellular organization and a distinct pattern of multiplication despite their simple structure they are a major cause of disease they have no cytoplasmic membrane cytosol or functional organelles, but they can infect all types of cells and numerous viruses can also infect bacteria which are called bacteriophage viruses



Bacteriophages are unable to do their metabolic activity on their own so instead, they attack other cells and gain their metabolic machinery to produce more viral molecules nucleic acid.



viruses can exist either extracellularly or intracellularly in the extracellular state the virus is called a virion and isn’t capable of reproducing very one consists of a protein coat called a capsid surrounding a nucleic acid core which contains the genetic material or the viral genome the nucleic acid and the capsid are collectively called a nucleic acid.


Envelope virus

some variants have a phospholipid membrane derived from the host cell called an envelope that surrounds the Nucleo capsid the viruses that have an envelope are called enveloped viruses and these include the herpes viruses and HIV.



while the ones that lack the envelope such as poliovirus are called non-enveloped or naked viruses once inside the cell the virus enters the intracellular state where the capsid is taken out, and the infection becomes dynamic in this express the infection exists exclusively as nucleic acids that actuate the host to orchestrate viral parts from which virions are gathered and eventually released now the viruses are surrounded by an outer protein coating called the capsid



which protects the viral genome and aids in its transfer between most cells also according to their capsid symmetry



capsid symmetry


The viruses can come in many shapes and sizes there are three types of shapes helical, icosahedral, and complex first the helical viruses have a capsid with a central cavity or a hollow tube which is made by proteins arranged in a circular fashion creating a disc-like shape the disc shapes are attached helical e creating a tube with room for the nucleic acid.


Example of a helical virus

In the middle, an example of a virus with helical symmetry is the tobacco mosaic virus which is the most studied.


Example of icosahedral viruses

example moving on to the icosahedral viruses which are made up of equilateral triangles that fuse together in a spherical shape that fully encloses the genetic material these viruses are released into the environment when the cell dies breaks down and lysis thus releasing the variants


some examples of icosahedral viruses include Poliovirus, Rhinovirus, and adenovirus finally the complex viruses have a combination of icosahedral and helical shapes and may have a complex outer wall or head-tail morphology


The head-tail morphology is unique to viruses that infect bacteria called bacteriophages and they have an icosahedral-shaped head and a helical-shaped tail these viruses use their tail to attach to the bacterium and then they create a hole in the cell wall and insert their DNA into the cell using the tail as a channel now the nucleic acid core of the virus contains the genetic material which can either be DNA or RNA and the total genetic content of the virus is called the viral genome


Viral genome

The viral genomes are usually small and contain only a few genes that encode for proteins needed by the virus that is not present in the host cell the genetic material can be single-stranded or double-stranded linear or circular in DNA viruses the viral DNA enters the nucleus and uses the hosts DNA polymerase to create more copies of itself as well as viral mRNA that gets translated into a viral protein with RNA viruses many of them stay in the cytoplasm


where the viral RNA is used by the host’s ribosomes to create viral RNA polymerase proteins these will help replicate the viral genome so that more viruses can be created RNA polymerases are more likely to make copying errors than DNA polymerases and therefore often make mistakes during transcription this is why mutations and RNA viruses occur more frequently than DNA viruses

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