Other cyanobacteria house chlorosomes , which contain pigments necessary for photosynthesis. The cytoskeleton of eukaryotes has long been noted and consists of a network of filaments for support and movement. The study used fluorescent antibodies to detect two proteins, termed MreB and Mbl, involved in making a helical internal scaffold responsible for maintaining cell shape. Bacterial cells can contain thousands of ribosomes , the sites of protein synthesis. The structural similarity of bacterial ribosomes to that of those found in eukaryotic mitochondria and chloroplasts has been interpreted as evidence of endosymbiotic theory .
Plasmids are small, extrachromosomal DNA circles.
Plasmids replicate independently of the chromosome carry genes that are not essential for cell survival but may give some advantage to an organism. For example, they can carry genes for antibiotic resistance and toxin production. Plasmids are also very useful vehicles for genetic engineering. The ability to produce spores is a type of cell differentiation involving precise genetic regulation of proteins. This process has now become a model system for studying how cells of higher organisms divide and differentiate.