The difference between bacteria and viruses

We have all gotten sick, we’ve all gotten some kind of flu and of course the classic cold. There is always talk about how we should protect ourselves from viruses and bacteria. But how are they even different? And how are they different to our most body cells. What if I told you that human cells have more in common with bacteria than with viruses.

Short story: Human cells are eukaryotic which means they are more complicated, bacteria cells are prokaryotic which means they are simpler and viruses are not even cells at all, they are just genetic material in a protein shell. Not all bacteria make us sick, most actually help us e.g. in our gut. Viruses are more like parasites they need a host cell to reproduce. Viruses are very specialized on their host so some only target certain human body cells (e.g. Herpes virus) and others attack certain bacteria.

Human cells

To make all of this more understandable let’s start with something you might be more familiar with: humans. We humans are multicelled organisms with an estimated 37 trillion cells in our body (over 5000 times more cells than people currently on earth). Our cells are eukaryotic. Because they having more organelles, they differ from prokaryotic cells (bacteria). Organelles are like the “organs” of a cell. They are specialized for different tasks for example the cell nucleus which stores the genetic information (DNA) or the ribosomes which build proteins.


A prokaryotic cell like a bacterium does not have a cell nucleus, the DNA just floats around in the cell. Bacteria are one celled organisms, each bacteria cell is independent from on another although they can interact with each other. Bacteria reproduce asexually by making an internal copy of themselves and then splitting, in a process called binary fission.

But both types of cells have a cell membrane which acts as a barrier between the inside of the cell and the outside environment. And this is where a virus can attack them.


Viruses are  just genetic material (DNA) in a protein shell. They can’t reproduce by themselves, they need a host cell. Viruses dock onto the membranes of their host cell (human cell or bacteria cells) and insert their genetic material into the cell.

Viruses attack a bacterium, Image credit: Wikimedia commons

The virus DNA manipulates the cell and turns it into a virus replication machine. All resources of the cell are spent on replicating (duplicates/copies) this viral DNA and producing protein shells to builds lots of different new viruses inside the cell. Then the cell is either programed to die and the cell bursts open releasing the viruses or the cell is kept alive and keeps realeasing viruses through its membrane.

The enemy of my enemy is my friend

As you now know a virus needs to kill its host cell to reproduce so they are all bad for us? Well, not all of them, there is a group called bacteriophages (bacteriakillers). Much like “the enemy of my enemy is my friend” these bacteriophages only infect bacteria and leave the human cells alone, so we can use them to combat harmful bacteria.

This was all very basic microbiology and the processes are a bit more complicated than I described here. So if you are interested check these great interesting videos out:
Bacteria: from Khan Academy
Viruses: from Khan Academy
How our immune system works to fight these: from Crash Course (one of my favorite youtube channels)

Sidenote: Are viruses evil?

You might think that a virus wants to kill us it wants to hurt us. But the Virus does not have a purpose to exist, it does not care about making us ill, it is not “evil”. The thing is that viruses which are good at reproducing exist. A virus which was bad at reproducing simply died out. But viruses which are good at reproducing survived. For example the flu virus: it makes us cough and sneeze and thus spreading the virus to other humans. It didn’t want to make us ill but those viruses that made us ill got spread more. They had an evolutionary advantage over viruses which were worse at reproducing, which died out.