In introductory biology courses, mitochondria are rarely covered beyond their “powerhouse of the cell” taglines.  However, what are depicted as bean-shaped organelles in every textbook, are actually complex, interconnected tubular mitochondrial networks coordinating cellular energy.

One of the main functions of mitochondria is producing ATP, the energy of cells, through oxidative phosphorylation.  Oxidative phosphorylation is the passing of electrons down the electron transport chain, which produces an electrochemical gradient across the inner mitochondrial membrane.  The energy stored in the gradient is then used to make ATP in a process called chemiosmosis.  But why is all of this relevant to marine mammals and hypoxia? Oxygen plays a huge role in oxidative phosphorylation! Oxygen accepts the electrons at the end of the electron transport chain and is key in keeping up the production of ATP.  Also, when electrons are not correctly passed through the electron transport chain, oxygen can be partially reduced and form Reactive Oxygen Species (ROSs).   Low levels of ROS are important for adaptations seen in hypoxia, and high levels of ROS activate cell death pathways. Therefore, in hypoxic conditions, the mitochondria must adjust to regulate ATP levels and manage ROS production.  Deep-diving marine mammals’ abilities to be highly functional with very little oxygen elucidates that there may be significant differences between human and marine mammal mitochondrial adaptations.