Video Transcript
Which of the following best
describes the role of chemiosmosis in oxidative phosphorylation? (A) Chemiosmosis is the movement of
electrons down their electrochemical gradient, which generates energy in the
electron transport chain. (B) Chemiosmosis is the chemical
breakdown of ATP into ADP and inorganic phosphate. (C) Chemiosmosis is the movement of
chemicals dissolved in water down their concentration gradient, across the
mitochondrial membrane. (D) Chemiosmosis is the chemical
breakdown of water into hydrogen and oxygen ions at the final stage of the electron
transport chain. Or (E) chemiosmosis is the movement
of ions down their electrochemical gradient, which generates ATP.
Let’s remove the answer options for
now so we can have a look at oxidative phosphorylation and the role of
chemiosmosis.
Oxidative phosphorylation is the
final stage of aerobic respiration, and it takes place in the inner mitochondrial
matrix of eukaryotic cells. In the inner mitochondrial matrix
is a collection of proteins, enzymes, proton pumps, and electron carriers that make
up the electron transport chain. Electrons donated by coenzymes move
through the electron transport chain, releasing energy as they do so. This energy is used by proton pumps
to actively transport hydrogen ions from the mitochondrial matrix and into the
intermembrane space. These hydrogen ions accumulate in
relatively high concentrations in the intermembrane space. They then move down their
electrochemical gradient from an area of high concentration to an area of low
concentration.
However, these hydrogen ions do not
simply move through the membrane but instead move through the channel of ATP
synthase. The movement of ions down their
electrochemical gradient is called chemiosmosis. The enzyme ATP synthase couples the
movement of hydrogen ions with the phosphorylation of ADP, which creates ATP. ATP is an energy-carrying molecule,
which is crucial in supporting a wide range of cellular reactions.
Let’s use what we now know about
chemiosmosis to answer this question. We now know that chemiosmosis is
the movement of ions down their electrochemical gradient. We also know that this movement of
ions is coupled to the production of ATP by ATP synthase. So our answer must be option
(E). In oxidative phosphorylation,
chemiosmosis is the movement of ions down their electrochemical gradient, which
generates ATP.
