Both viruses and bacteria are so small that you cannot see them in plain sight (although viruses are, depending on the type, between 10 and 100 times smaller than bacteria) and that is why both are called microorganisms. However, the main difference between viruses and bacteria is that bacteria are considered living beings, but viruses are not. Why? Living beings, by definition, can nurture, relate and reproduce. While bacteria can reproduce on their own, viruses need to enter in a living being (for example, a cell) which is able to reproduce itself and use this ability to reproduce themselves: without this cell, viruses cannot reproduce. For this reason, viruses are not considered living beings but “cellular” parasites.

The genetic material contained by bacteria and viruses is also different. Brief reminder: the genetic material harbors all the information necessary for the organism to work. In living beings, this information is encoded in the deoxyribonucleic acid (DNA), which is a very stable type of molecule. To transmit this information within the cell, this information is temporarily copied into another less stable type of molecule (ribonucleic acid or RNA), which will take this information wherever is necessary in the cell. In contrast to bacteria, which only use DNA structured in a circular form, viruses (again, depending on the type) use both DNA and RNA in either circular or linear form.

Finally, viruses’ structure is way simpler than bacteria’s. Viral genetic material is wrapped in a protein layer, and some types of viruses are additionally protected by a pseudomembrane (fun fact COVID19: this protective pseudomembrane is the part of the virus destroyed by soap). However, bacterial organization is more complex: it has several structures which take care of different functions (organelles) and all of them, together with the genetic material, are surrounded by a cellular membrane. Moreover, this membrane is protected by a rigid layer called the cell wall.

Knowing these four differences, you will never confuse again a bacterium with a virus… even if you cannot see them!