Mitochondria may have a number of different shapes. A mitochondrion contains outer and inner membranes composed of phospholipid bilayers and proteins. The two membranes have different properties. Because of this double-membraned organization, there are five distinct parts to a mitochondrion:
# The outer mitochondrial membrane,
# The intermembrane space (the space between the outer and inner membranes),
# The inner mitochondrial membrane,
# The cristae space (formed by infoldings of the inner membrane), and
# The matrix (space within the inner membrane), which is a fluid.
Mitochondria have folding to increase surface area, which in turn increases ATP (adenosine triphosphate) production.
Mitochondria stripped of their outer membrane are called mitoplasts.