8. Respiration

Chemiosmotic creation of ATP is driven by:

a) Phosphate transfer through the plasma membrane.

b) Potential energy of the H⁺ concentration gradient created by the electron transport chain.

c) Substrate-level phosphorylation in the mitochondrial matrix.

d) Large quantities of ADP in the mitochondrial matrix.

The electron transport chain pumps H⁺ ions into which location of the mitochondria?

a) Mitochondrial intermembrane space. 

b) Mitochondrial matrix.

c)  Mitochondrial inner membrane.

d) The H⁺ ions are pumped out of the mitochondria.

What does the chemiosmotic hypothesis claim? a. ATP is generated using phosphates taken from intermediates in the electron transport chain. b. ATP is generated using a phosphate gradient produced by glycolysis and the citric acid cycle. c. ATP is generated using a proton-motive force that is produced by the electron transport chain. d. Water is generated using electrons taken from NADH and FADH2 and transported through the electron transport chain.

MAKE CONNECTIONS The proton pump shown in Figures 7.17 and 7.18 is a type of ATP synthase (see Figure 9.14). Compare the processes shown in the two figures, and say whether they are involved in active or passive transport (see Concepts 7.3 and 7.4).

VISUAL SKILLS This computer model shows the four parts of ATP synthase, each part consisting of a number of polypeptide subunits (the structure in gray is still an area of active research). Using Figure 9.14 as a guide, label the rotor, stator, internal rod, and catalytic knob of this molecular motor.

Continue your comparison of electron transport and chemiosmosis in mitochondria and chloroplasts. In each case, a. where do the electrons come from? b. how do the electrons get their high potential energy? c. what picks up the electrons at the end of the chain? d. how is the energy released as electrons are transferred down the electron transport chain used?

For a short time in the 1930s, some physicians prescribed low doses of a compound called dinitrophenol (DNP) to help patients lose weight. This unsafe method was abandoned after some patients died. DNP uncouples the chemiosmotic machinery by making the inner mitochondrial membrane leaky to H+. Explain how this drug could cause profuse sweating, weight loss, and possibly death.