- The bacterial cytoplasm is not sub-divided by any additional membranous compartments. Consequently, bacteria do not possess a distinct nucleus like mammalian cells. Major structural features of the cytosol are discussed below.
- The bacterial genome is composed of a single, circular molecule of DNA. Importantly, bacterial genes does not contain introns like their mammalian counterparts. Bacterial genes are transcribed into mRNA which then goes on to be translated by bacterial ribosomes (see below). Interestingly, bacterial mRNA molecules are "polycistronic" and may contain several genes which are translated into separate proteins. In contrast mammalian mRNA molecules are "monocistronic" and contain information for only a single gene.
- In addition to the bacterial genome, much smaller circular pieces of double-stranded DNA, termed plasmids, can replicate and exist independently in the bacterial cytoplasm. Plasmids often contain genes that allow for the synthesis of bacterial virulence factors or antibiotic resistance proteins. Many plasmids can be exchanged with other bacteria through "Bacterial Conjugation" as described in Bacterial Genetics.
- Bacterial ribosomes are basically similar to mammalian ribosomes, but do contain significant structural differences. Bacterial ribosomes are smaller, being composed of 50S and 30S subunits which together make up a 70S ribosome whereas the mammalian ribosome is made up of 60S and 40S subunits which together make an 80S ribosome. The antibiotic pharmacological class of Bacterial Ribosome Inhibitors inhibit the bacterial (but not mammalian) ribosome and in so doing selectively inhibit bacterial protein synthesis and thus growth.