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.


  • Outer Membrane
    • Encloses the entire organelle. It has a protein-to-phospholipid ratio similar to that of the eukaryotic plasma membrane. It contains numerous integral proteins called PORINS.
  • Intermembrane Space (space between the outer and inner membranes)
  • Inner Membrane
    • Contains Proteins with four types of functions:
      • Those that carry out the oxidation reactions of the respiratory chain (ETC)
      • ATP synthase, which makes ATP in the matrix
      • Specific transport proteins that regulate the passage of metabolites into and out of the matrix
      • Protein import machinery
    • Contains more than 100 different polypeptides
    • Has very high protein-to-phospholipid ratio (1 protein for 15 phospholipids)
    • Rich in an unusual phospholipids, CARDIOLIPIN, which was first discovered in beef hearts in1942 and is usually characteristic of mitochondrial and bacterial plasma membranes.
    • Unlike the outer membrane, the inner membrane does not contain porins and is highly impermeable; almost all ions and molecules require special membrane transporters to enter or exit the matrix. There is a membrane potential across the inner membrane.
    • The inner mitochondrial membrane is compartmentalized into numerous cristae, which expand the surface area of the inner mitochondrial membrane enhancing its ability to generate ATP.
    • Mitochondria of cells that have greater demand for ATP = Increased/high/more cristae present
  • Cristae Space
  • Mitochondrial matrix
    • The space enclosed by the inner membrane. Matrix is important in the production of ATP with the aid of the ATP synthase contained in the inner membrane.