Outer Membrane Function

• Mitochondria consist of an outer and inner membrane. Each plays an essential function in the production of ATP. The outer membrane serves as a gatekeeper, keeping out unwanted substances and allowing small molecules and ions to enter. It contains channels that exist due to porin, a protein. These channels keep out molecules deemed too large. The molecules that pass through the outer membrane enter an inter-membrane space before encountering the inner membrane.
  
  

Inner Membrane Function

• The inner membrane, or cristae, is a closed space that contains a matrix and the production site of ATP. The inner membrane contains infoldings that allow only certain select small molecules to enter the matrix. Those molecules enter via a system of transport proteins. The infoldings serve to increase the surface area of the inner membrane, which enables the mitochondria to host more enzymes for respiration.
  
  

Aerobic Respiration

• Those enzymes in the inner membrane provide part of the material necessary for aerobic respiration, a process in the mitochondria that transforms oxygen into ATP. The enzymes combine with protein in the inner membrane as part of respiration. The ATP produced by this process goes into the body as its energy supply.
  
  

Reproduction and Presence

• Mitochondria contain their own DNA and reproduce separate from their host cell. The DNA is in the matrix. All living cells contain mitochondria, with the number depending upon the amount of energy that cell requires. Cells in muscles and fat cells require large numbers of mitochondria to function and generate the necessary energy.