Bacterial Cell Structure

While not all bacteria share the same rod-like shape of the model pictured here, they all have similar structures.  At the center of the cell is usually a single chromosome.  Like the DNA or RNA in animal or human cells, the bacterial chromosome has full capability to replicate itself.  

Unlike higher organisms, the bacteria's chromosome is not protected from the cytoplasm (fluid of the cell) by a nuclear membrane (such as in the nucleus of a protozoan).

Also, bacteria may have extra pieces of DNA (called plasmids), as well as ribosomes (they help the chromosome replicate) in the cytoplasm. Plasmids confer certain advantages on their host bacterium. These may include genes for resistance to antibiotics. Plasmids also have a DNA sequence that triggers replication of the plasmid independently of the replication of the main DNA in the chromosome. Genetic engineering techniques often insert foreign DNA into bacteria in the form of plasmids, which then multiply in the bacterium.

Lastly, some bacterial species have flagella to help them move around.  Other species may have a rugged cell wall outside the delicate cell membrane.