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Viruses

An image of a virus particle


Viruses cause diseases such as the common cold, COVID-19, mumps, measles, HIV and Polio to name but a few. It is common at A Level to be asked why viruses are classed as 'non-living' or why antibiotics are not used when someone is infected by them. In this post, we will discuss the answers to these two important questions and explain what a virus is.

 What is a Virus and what does it do?

A Virus has a protein coat (a Capsid) surrounding a piece of DNA or RNA (Nucleic Acid. In some viruses there is an additional lipid layer on the outside of the capsid. The proteins can stick out from the surface (sometimes projecting through the lipid layer) and these are referred to as 'spike proteins.'  

A virus attaches to living cells and either enters the cell whole or injects its Nucleic Acid into the host cell. The host cell then copies the nucleic acid and uses it to produce more virus capsids. The virus particles are assembled in the cell and then leave it to infect more cells. In this way they are using the host cell's organelles to make virus copies. They can be transferred from one host to another via blood or mucus.


 Why is a virus non living?

Viruses are non living. They are not like animals, plants, fungi, protists and bacteria. These are all living and are made up of one or more cells. Viruses are not made of cells and are instead referred to as 'particles.'

Viruses are not classed as living organisms because they do not possess all the characteristics of living things. See  "The features of all living organisms" to find out which characteristics viruses do not possess.

 Why do antibiotics not work against viruses?

Antibiotics are chemicals used to kill bacterial cells or stop them from multiplying inside animals. They work against bacteria in one of three main ways:

  • Prevent DNA synthesis by interfering with bacterial enzymes that copy DNA
  • Prevent protein synthesis by interfering with bacterial enzymes that produce proteins
  • Inhibit the synthesis of the bacterial cell wall

Since they target bacterial enzymes only and viruses have no enzymes anyway, antibiotics are useless against a viral infection. In fact, using antibiotics when they are not needed increases the chances of bacteria becoming resistant to them. So they should only be taken as prescribed for a bacterial infection. 

The features of all living organisms: 

The features of all living organisms are listed below . Test yourself by considering each feature in turn . Think about what the statement means then click on the box to see if you are correct. 


Explaining viruses clearly 

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