Mitochondria:
Though they are indeed membranous, the mitochondria are
not formed by or associated with the endoplasmic reticulum, Golgi bodies, or other membranous organelles. As such, mitochondria are not considered part of the endomembrane system of a cell.
A mitochondrion looks somewhat “sausage-shaped” under a microscope, and it has an elaborately folded inner membrane. The mitochondria are where
aerobic (
cellular)
respiration occurs. That is, the mitochondria are where
carbohydrate molecules are
decomposed in order to release the energy that powers the cell’s
metabolism.
Interestingly, mitochondria have their own
DNA, and mitochondria reproduce independently of the rest of the cell. Analysis of mitochondrial DNA shows that it’s actually much more similar to the DNA of certain bacteria than it is to the DNA in the nucleus of the cell within which it resides.
Given the similarity of mitochondrial DNA to bacterial DNA, it is thought that mitochondria are the descendants of bacterial cells that – at some time in the distant past – either invaded larger cells or were engulfed by them. In either case, these cells weren’t destroyed in the process. Instead, the bacterial cells remained within the larger cells and the arrangement turned out to be mutually beneficial. The bacterial cells gained a (relatively) safe and stable haven, and the larger cells benefited from the energy the bacterial cells produced when they broke down carbohydrates.
A mitochondrion within a cell.
Mitochondria
Linear Mode
