Prokaryotic cells and viruses

Viruses are acellular, non-living particles. They are smaller than bacteria, ranging in size from 20-300 nm. 

They contain nucleic acids such as DNA or RNA as genetic material but can only multiply in living host cells. 

The nucleic acid is enclosed within a protein coat called the capsid. 

Some viruses, like the human immunodeficiency virus, are further surrounded by a lipid envelope. 

Or if this isn't present, the capsid, have attachment proteins which are essential to identify the host and attach to it.

Bacteria are highly adaptable and versatile leading to them to occur in every habitat in the world. 

Their cellular structutre is relatively simple:

• Cell wall made up of miuren - Polymer of polysaccarides and peptides. Many other bacteria protect themselves further by secreating themselves in mucilagious slime around them. 
• Inside they have a cell surface membrane.
• Cytoplasm that contain ribosomes- These ribosomes are smaller than those found in eukaryotic cells.
• Bacteria store food as glycogen granules and oil droplets.
• Circular strand of DNA - Seperate from this are circular plasmids of DNA.

These can reproduce themselves independently and therefore may give bacterium resistance to harmful chemicals, such as antibiotics. 

Plasmids are used havily as vectors (carriers of genetic information)