What are the differences between a bacterium and a virus?
I guess there are lots of differences that one could suggest, but for me the defining one is the fact that bacteria can replicate itself without the help of a host cell. A virus cannot replicate independently.
There are several other differences, all of which are directly or indirectly related to the above:
- Viruses do not carry their own enzymes for making proteins, nor do they contain ribosomes which are contained in bacteria for protein production.
- Viruses do not have a cell membrane or a cell wall.
- Viruses tend to be much smaller than bacteria and are often only visible with the use of an electron microscope.
- Viruses are not treatable with antibiotics. Some viruses however can be treated with effective anti-viral compounds.
- Viruses cannot be cultured on agar plates like most bacteria. They require living cells in the form of cell cultures.
What are the main constituents of a bacterial cell?
Bacteria are efficient replicating machines and survival experts thus all their consituents serve a function to these purposes.
Best to “break down” a bacterium into what is inside the cell, what is on the surface of the cell and what is attched to the surface.
Inside a bacterium:
- Nucleoid area containing DNA. Note this is not a nucleus
- Ribosomes: Area where proteins are synthesized.
- Cytoplasm: Contains nutrients, proteins and enzymes, mostly associated with allowing the bacterium to replicate.
On the surface of a bacterium: (from inside to out)
- Cell membrane: Mediates transport of substances in and out of teh bacterium. Conatains enzymes
- Cell wall: Thinner in Gram negative bacteria than in Gram Positive. Confers rigidity to the cell. Also acts as a permeability barrier.
- Capsule (not in all bacteria) : Protects against phagocytosis. Can prevent dessication of the cell.
Attached to the surface of a bacterium
- Sex Pili (not in all bacteria): Allows DNA transfer between bacteria by conjugation.
- Flagellae (not in all bacteria): Gives motility to the bacterium, allowing it to find an area where it can survive best.
- Fimbriae: also called common pili. Facilitates attachment to cells eg epithelial cells.
Try and draw a schematic bacterium to see if you know the basic structure.
Of course there are some bacteria which have more specialisd components and functions. If you are looking for a distinction in an exam you will need to know about these. Consider things like plasmids, cytoskeleton, vesicles, slimes layers. The list goes on…
Further reading:
Todar’s bacteriology: Cell structure.
Wikipedia: Bacterial cell structure.