• Question: What's the difference between bacteria and virus?

    Asked by sulty4skin to PB, Paul, Lyn, Katy on 26 Jun 2013.
    • Photo: Peter Balfe

      Peter Balfe answered on 26 Jun 2013:

      A virus is the truest parasite, it has no metabolism of it’s own relying totally on its host, whereas a bacteria does. That’s the key difference.
      The classic 3 word phrase is :
      OBLIGATE
      INTRACELLULAR
      PARASITE
      I get my first year undergraduate class to chant this out loud during lectures.

    • Photo: Paul Waines

      Paul Waines answered on 26 Jun 2013:

      Hi sulty4skin- first of all viruses are way way smaller than bacteria- about 0.1 microns ( that’s a tenth of a millionth of a metre!)
      Secondly, a virus is really a ‘particle’ whereas bacteria are cells. That is to say that they are not able to survive on their own, whereas bacteria can, because they are more complex.

      This means that viruses have to invade cells (including bacteria) to make copies of themselves- this makes them parasites; they use the cells and don’t give anything back!

    • Photo: Ee Lyn Lim

      Ee Lyn Lim answered on 27 Jun 2013:

      There is this idea that life essentially consists of passing on your genes (i.e. making more of your species). Viruses take this extremely literally, since they are actually just strands of genetic material (DNA or RNA) and a protein container (called a capsid) to put them in! That’s why it’s not completely agreed that viruses are alive at all – they don’t eat, they don’t breathe – all they do is bind to cells with their capsid, inject their genetic material into those cells, and then have the infected cells make many many copies of both their genetic material and the bits of protein to build the capsid with, so that they can be packaged into new viruses. (Remember DNA, or in some cases RNA, acts like a set of instructions that tells the cell how to behave, so if you stick some foreign DNA into a cell you can get it to do things it doesn’t normally do – like make baby viruses!) That’s why they can’t do anything without a host cell to infect – if you have a single virus in a sugar solution and nothing else, you can come back days later and it will stay just like that – a single virus.

      Bacteria, on the other hand, are much more like the living things that we think of – they need water and nutrition to survive. Like a cell, bacteria are made of a membrane of lipids and carbohydrates, around a watery soup of proteins as well as a strand of DNA. They can swim around in water (as Paul can probably tell you), move towards areas with more nutrients, and reproduce by growing larger and splitting into two. If you left one bacterium in a sugar solution for a few days, you’d probably come back to millions and millions of bacteria munching away on the sugar! Many kinds of bacteria are quite happy living on their own out in some pond in the wild, and never cause any infections or disease at all; some strains of bacteria can even do photosynthesis like plants, and make their own food from carbon dioxide and sunlight. Of course, some bacteria do also infect hosts and depend on them to survive, but most often what they get from the host is just food, rather than making the host help them reproduce!

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