Two papers published recently, one in the journal Science and another in the Cell, have generated new interest in the endosymbiotic theory.
- The endosymbiotic theory states that organelles like mitochondria and chloroplasts, the sites of cellular respiration and photosynthesis, were once free-living bacteria that were later ingested by the recipient cells.
Prokaryotes vs Eukaryotes
- There are many millions of life forms on earth, all of them are made up of only two basic types of cell: prokaryotes and eukaryotes.
- Prokaryotes are small and simple and have rings of circular DNA floating free inside the cell. Eukaryotes are large and more complex. They have a nucleus, which holds strings of linear DNA within a lipid membrane.
- All the life forms that we are used to seeing – animals (including humans), plants, and fungi – are made up of eukaryotic cells.
- The bacteria, which are too small to see without a microscope, are made up of prokaryotic cells.
- Prokaryotes were around for a long, long time before eukaryotic cells appeared around 1.8 billion years ago.
