Jordana Cepelewicz writes:

Open a basic biology textbook published decades ago or one published a few months ago, and both will define the two major categories of cells in the same way: Eukaryotes have membrane-bound compartments called organelles, including a nucleus where they store their genetic information, while prokaryotes do not. The distinction is even embedded in their names: In Greek, the word “eukaryote” means “true kernel” (a reference to the nucleus), while “prokaryote” means “before kernel.”

As the evolutionary story is usually told, first came the prokaryotes: the archaea and bacteria, which are often envisioned as simple bags of enzymes without an intricate structure. Then, more than 1.5 billion years ago, eukaryotes evolved, marking the advent of unprecedented cellular complexity and permanently transforming life on Earth, allowing for the rise of animals, plants, fungi and protists. The eukaryotes represented a substantial departure from their predecessors, and the transition from an all-prokaryote world to one that contained eukaryotes is often described as abrupt and explosive.

But this version of events ignores the fact that, for the past few decades, researchers have been quietly uncovering many complex structures within prokaryotes, including membrane-bound organelles. In contrast to eukaryotes, which all have a suite of organelles in common, different groups of prokaryotes showcase their own specialized compartments. One kind of bacterial organelle, discovered in 1979, is essentially a little magnet wrapped in a lipid package; another hosts a series of reactions crucial for energy metabolism; still others serve as small storage units for nutrients. [Continue reading…]