what is the main topic in discussion?
Mitochondrion.
Mitochondrion
A mitochondrion contains outer and inner membranes composed of phospholipid bilayers and proteins. 
where is the mitochondria located in an animal cell UNANSWERABLE
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Mitochondrion [SEP] Structure
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. They are: Mitochondria stripped of their outer membrane are called mitoplasts.