The mitochondrion (plural, mitochondria) is a type of organelle that specializes in making ATP (molecule used by cells as main energy source). They have various enzymes to catalyze cellular respiration. Bacteria have no mitochondria; they make ATP in their cell walls and cytoplasm. Cells that have a very high demand for energy tend to have many mitochondria e.g. liver needs more because needs more energy. Mitochondria, like most organelles, can move within the cell and they grow and divide independently. Each has two membranes, one highly folded inside the other. Double-membrane system: Smooth outer membrane (lipid bilayer) faces cytoplasm and permeable to small solutes; blocks macromolecules where as Inner Membrane (cristae) folds back on itself to enlarge surface area for chemical reactions to take place. Membranes form two distinct compartments. ATP-making machinery is embedded in the inner mitochondrial membrane.
- Mitochondria and chloroplasts have similarities with bacteria,
- Enveloped by a double membrane
- Contain free ribosomes and circular DNA molecules
- Grow and reproduce somewhat independently in cells
They may have evolved from ancient bacteria that were engulfed but not digested. Mitochondria and chloroplasts developed because as a prokaryote it gained protection by living inside the eukaryote and in turn produced energy for the eukaryote (symbiotic relationship).