Eukaryotic cells arose long after prokaryotic cells. Some organelles may have evolved by infolding of the cell membrane, whereas others probably evolved by endosymbiosis.
learning outcomes
You should be able to:
Explain how the cell membrane could have been involved in the evolution of the endomembrane system in eukaryotes.
Relate endosymbiotic theory to observations of modern cells.
How could membrane infolding in a prokaryotic cell lead to the formation of the endomembrane system?
The cell membrane could fold inward and then pinch off, forming vesicles for the Golgi apparatus and flat sheets for the ER.
When they are removed from a cell, organelles such as mitochondria no longer function as they did inside the cell. What aspect of endosymbiotic theory explains this observation?
The endosymbiotic theory states that one cell engulfed another cell. Over time the engulfed cell lost some DNA and the ability to perform independently of the host cell. Thus the engulfed cell became dependent on the host cell for its survival.
In this chapter we presented an overview of the components of cells, with some ideas about their structures, functions, and origins. As you now embark on the study of major cellular processes, keep in mind that cellular components do not exist in isolation: they are part of a dynamic, interacting system. In Chapter 6 you will see that the cell membrane is far from a passive barrier, but instead is a multifunctional system that connects the inside of the cell with its extracellular environment.