Ch. 9 Test Your Understanding

The IMMEDIATE energy source that drives ATP synthesis by ATP synthase during oxidative phosphorylationis is the...

H+ concentration gradient across the membrane holding ATP synthase.

DRAW IT : The graph here shows the pH difference across the inner mitochondrial membrane over time in an active respiring cell. At the time indicated by the vertical arrow, a metabolic poison is added that specifically and completely inhibits all function of mitochondrial ATP synthase. Draw what you would expect to see for the rest of the graphed line, and explain graph.

H+ would continue to be pumped across the membrane into the intermembrane space, increasing the difference between the matrix pH and the intermembrane space pH. H+ would not be able to flow back through ATP synthase, since the enzyme is inhibited by the poison, so rather than maintaining a constant difference across the membrane, the difference would continue to increase. (Ultimately, the H+ concentration in the intermembrane space would be so high that no more H+ would be able to be pumped against the gradient, but this isn't shown in the graph.)

MAKE CONNECTIONS : Step 3 in Figure 9.9 is a major point of regulation of glycolysis. The enzyme phosphofructokinase is allosterically regulated by ATP and related molecules (see concept 8.5). Considering the overall result of glycolysis, would you expect ATP to inhibit or stimulate activity of this enzyme? Explain. (hint : make sure you consider the role of ATP as an allosteric regulator, not as a substrate of the enzyme.)

Since the overall process of glycolysis results in net production of ATP, it would make sense for the process to slow down when ATP levels have increased substantially. Thus, we would expect ATP to allosterically inhibit phosphofructokinase.

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).

The proton pump in Figures 7.17 and 7.18 is carrying out active transport, using ATP hydrolysis to pump protons against their concentration gradient. Because ATP is required, this is active transport of protons. The ATP synthase in Figure 9.14 is using the flow of protons down their concentration gradient, no energy is required, and this is passive transport.

Which metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule?

glycolysis

The final election acceptor of the electron transport chain that functions in aerobic oxidative phosphorylation is...

oxygen

In mitochondria, exergonic redox reactions...

provide the energy that establishes the proton gradient

What is the oxidizing agent in the following reaction?... Pyruvate + NADH + H+ S Lactate + NAD+

pyruvate

Most CO2 from catabolism is released during...

the citric acid cycle

When electrons flow along the electron transport chains of mitochondria, which of the following changes occurs?

the pH of the matrix increases