Question

When electron flow along the electron transport chains of mitochondria, which of the following changes occur?
A) pH of the matrix increases
B) $NA{{D}^{+}}$is oxidized
C) Cytochromes of the chain phosphorylate ADP to form ATP
D) ATP synthase pumps protons by active transport

Answer 1

Hint: The electron transport chain is a chain of or group of proteins in the mitochondria which through a series of redox reactions forms ATP and water molecules as a result. There are four complexes numbered I to IV.

Complete answer:
- The last component of aerobic respiration is the electron transport chain.
- Glucose metabolism which uses atmospheric oxygen is the only part of the electron transport chain.
- Just like a relay race in which the bate is passed from one player to the next player, the electrons are passed rapidly from one complex to the next.
- The complexes are embedded in the Cristae which is the inner mitochondrial membrane.
- Initially to start two electrons to the first complex (complex I).
- Complex II directly receives $FAD{{H}_{2}}$ and the compound ubiquinone (Q) connects first and second complex to the third complex.
- Protons are pumped by complex III through the membrane.
- In the fourth complex, the oxygen reduces and picks the two hydrogen ions to make ${{H}_{2}}O$.
- Finally, in the process of chemiosmosis the free energy is used to pump hydrogen ions.
- Overall redox reaction is: $2{{H}^{+}}+2{{E}^{+}}+\dfrac{1}{2}{{O}_{2}}\to {{H}_{2}}O+energy$
- Hence, we can conclude that ATP synthase pumps protons by active transport since ATP is being synthesized.

Hence the correct answer is option ‘D’.

Note: All the four complexes take place in the inter membrane space of the mitochondrial matrix. The end point of the electron transport chain is where the electrons reduce molecular oxygen to produce water.