Mitochondria provides the energy a cell needs to move, divide, produce secretory products, contract - in short, they are the power centers of the cell. They are about the size of bacteria but may have different shapes depending on the cell type.
The mitochondria contain their own DNA, which is circular as is true with bacteria, along with their own transcriptional and translational machinery.
They are the organelles that act like a digestive system that takes in nutrients, breaks them down, and creates energy for the cell. The process of creating cell energy is known as cellular respiration.
A mitochondrion contains inner and outer membranes composed of phospholipid bilayers and proteins. The two membranes have different properties.