What exactly is a virus?

What exactly is a virus? Is it considered life? Why can’t I just take antibiotics to get rid of a cold? To find the answers to these questions, I could just link the Wikipedia article for you and send you on your way. But that isn’t the point of this blog!

To quote Medline Plus, a medical dictionary supported by the NIH, a virus is

“any of a large group of submicroscopic infective agents that are regarded either as extremely simple microorganisms or as extremely complex molecules, that typically contain a protein coat surrounding an RNA or DNA core of genetic material but no semipermeable membrane, that are capable of growth and multiplication only in living cells, and that cause various important diseases in humans, animals, or plants”

While this definition explains what a virus is, it doesn’t really explain what a virus really is.

What is a virus?     

Viruses are minute infectious particles that tread the line between living and non-living. They infect their hosts and take over cellular machinery to replicate without expending any energy themselves. Their genetic code, consisting of either DNA or RNA, only contains the details needed to allow for proper function and continuation of their infectious cycles.

All viruses have their genetic information surrounded by protective protein wrapping called a capsid. Capsids can form several different shapes and prevents the genetic material of the virus from the cell’s defense system. Some viruses are able to take the cell membrane of the cell they infect and make another envelope from it, further protecting the virus from being degraded. Scientists classify viruses by the type of genetic material they carry and the shape of their capsid.

How big are viruses?

Despite their tiny size, these infectious agents can do a lot of damage. To put in perspective how small viruses are, if bacteria were scaled to the size of the Superdome, a virus would only be the size of Jimmy Graham on the field!  This website offers a great animation on the relative size of viruses compared to other tiny objects like bacteria, dust, and pollen.

How do viruses work?

Viruses do not have the capacity make more of their own genetic material, so they rely on the cells they infect to copy their genetic material for them. After the infected cell has made new copies of the viral genome and when the virus is ready, the cell bursts open to release the virus. The virus can continue infecting, replicating inside, and killing cells in this fashion. So are viruses living organisms or not? That remains a debate for another day.

Of course, some types of viral infections are more dangerous than others. Did you know that over 90 percent of the American population has been infected with Epstein-Barr virus, a virus that infects B cell lymphocytes and can cause “mono”, at some point in their lives? Yet for a large majority of us, the only signs we show of it are no different from a mild cold. On the other hand, untreated contact with the Rabies virus is deadly.

Different viruses infect different types of cells. For example, HIV infects CD+4 T-cells, a type of white blood cell involved in immunity. Influenza (the virus that causes the flu) infects certain types of epithelial cells lining the nose, throat, lungs, and intestines. The site of infection, as well as the type of cells infected and amount of virus present are all factors in determining how potent a virus can be.

Alright… but why can’t I take antibiotics when I get a cold? Don’t they kill everything?

The reason antibiotics don’t work on viruses is because the compounds that antibiotics attack specific structures in bacteria cells that viruses simply don’t have. Taking a round of antibiotics at the first sign of a cold or flu will not help you feel better sooner, and may actually cause more harm than good. That said, there are antiviral therapies that can be prescribed by your doctor if he or she determines that you have a viral infection.

Sources:

1: Harvey SC, Zeng Y, Heitsch CE. The icosahedral RNA virus as a grotto:
organizing the genome into stalagmites and stalactites. J Biol Phys. 2013
Mar;39(2):163-72. doi: 10.1007/s10867-013-9312-1. Epub 2013 Apr 27. Review.
PubMed PMID: 23860866; PubMed Central PMCID: PMC3662420.
2: Knobler CM, Gelbart WM. Physical chemistry of DNA viruses. Annu Rev Phys Chem.
2009;60:367-83. doi: 10.1146/annurev.physchem.59.032607.093728. Review. PubMed
PMID: 19046126.
3: Affranchino JL, Gonzalez SA. Understanding the process of envelope
glycoprotein incorporation into virions in simian and feline immunodeficiency
viruses. Viruses. 2014 Jan 16;6(1):264-83. doi: 10.3390/v6010264. Review. PubMed
PMID: 24441862; PubMed Central PMCID: PMC3917442.

 

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