Energy Organelles
Mitochondria and Chloroplasts are the organelles that convert energy, that they acquire from their surroundings, to forms that cells can use for work. The main form of energy that cells can use is called adenosine triphosphate or ATP.
The endosymbiont theory is the largely accepted hypothesis as to how energy organelles came to exist in eukaryotic cells. It states that an early ancestor of the eukaryotic cells engulfed an oxygen-using non photosynthetic prokaryotic cell. Eventually the two cells formed a relationship and the engulfed cell became an endosymbiont (a cell living within another cell). Later these cells merged into a single organism, making a eukaryotic cell with a mitochondrion. For the chloroplast, one of these cells may have taken up a photosynthetic prokaryote, which then became the ancestor of eukaryotic cells with chloroplasts.
This theory helps explains many structural features of the two organelles.
The endosymbiont theory is the largely accepted hypothesis as to how energy organelles came to exist in eukaryotic cells. It states that an early ancestor of the eukaryotic cells engulfed an oxygen-using non photosynthetic prokaryotic cell. Eventually the two cells formed a relationship and the engulfed cell became an endosymbiont (a cell living within another cell). Later these cells merged into a single organism, making a eukaryotic cell with a mitochondrion. For the chloroplast, one of these cells may have taken up a photosynthetic prokaryote, which then became the ancestor of eukaryotic cells with chloroplasts.
This theory helps explains many structural features of the two organelles.
- Most organelles of the endomembrane system are bound by a single membrane but both chloroplast and mitochondrion are bound by two membranes. This is evidence that the engulfed prokaryotes had two outer membranes which then became the double membranes of chloroplast and mitochondria.
- Like prokaryotes both organelles contain ribosomes, as well as circular DNA molecules attached to their inner membranes. The DNA programs the synthesis of some proteins, which are made on the ribosomes.
- They are autonomous organelles that grow and reproduce within the cell. Their shape is changeable, they grow and occasionally pinch in two reproducing themselves, and they are mobile within the cell.