Mastering Biology Chapter 9 Pre-Lecture Assignment 2

What are not inputs or outputs of acetyl CoA formation?

ATP, ADP, glucose, O2

Where does glycolysis occur?

In the cytosol.

Where does oxidative phosphorylation occur?

In the inner mitochondrial membrane.

Where does acetyl CoA occur?

In the mitochondrial matrix.

Where does the citric acid cycle occur?

In the mitochondrial matrix.

What are the net inputs of glycolysis?

NAD+, ADP, glucose

What are the net outputs of the citric acid cycle?

NADH, CO2, ATP, coenzyme A

What are the net inputs of oxidative phosphorylation?

NADH, O2, ADP

What are not inputs or outputs of the citric acid formation?

O2, glucose, pyruvate

What are the net inputs of the citric acid cycle?

acetyl CoA, NAD+, ADP

What are the net outputs of acetyl CoA formation?

acetyl CoA, NADH, CO2

How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.) a. Electron transport would be unaffected but ATP synthesis would stop. b. Electron transport would stop but ATP synthesis would be unaffected. c. Both electron transport and ATP synthesis would stop. d. Neither electron transport nor ATP synthesis would be affected.

c. Both electron transport and ATP synthesis would stop. Oxygen plays an essential role in cellular respiration because it is the final electron acceptor for the entire process. Without O2, mitochondria are unable to oxidize the NADH and FADH2 produced in the first three steps of cellular respiration, and thus cannot make any ATP via oxidative phosphorylation. In addition, without O2 the mitochondria cannot oxidize the NADH and FADH2 back to NAD+ and FAD, which are needed as inputs to the first three stages of cellular respiration.

What are not inputs or outputs of glycolysis?

coenzyme A, CO2, acetyl CoA, O2

What are the net inputs of acetyl CoA formation?

coenzyme A, NAD+, pyruvate

Net redox reaction in acetyl CoA formation and the citric acid cycle. In the sequential reactions of acetyl CoA formation and the citric acid cycle, pyruvate (the output from glycolysis) is completely oxidized, and the electrons produced from this oxidation are passed on to two types of electron acceptors.

pyruvate is oxidized to (a) CO2 NAD+ is reduced to (b) NADH (c) FAD is reduced to (d)FADH2

What are the net outputs of glycolysis?

pyruvate, ATP, NADH

What are the net outputs of oxidative phosphorylation?

water, NAD+, ATP

Carbon atoms in acetyl CoA formation and the citric acid cycle During acetyl CoA formation and the citric acid cycle, all of the carbon atoms that enter cellular respiration in the glucose molecule are released in the form of CO2. Use this diagram to track the carbon-containing compounds that play a role in these two stages.

Start: acetyl CoA - 2 C; continue clockwise: 6 C, 6 C, 5 C, 4 C, 4 C, 4 C, 4 C, 4 C

During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell's demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions. What would happen to the cell's rate of glucose utilization? a. Glucose utilization would increase a lot. b. Glucose utilization would increase a little. c. Glucose utilization would remain the same. d. Glucose utilization would decrease a little. e. Glucose utilization would decrease a lot.

a. Glucose utilization would increase a lot. ATP made during fermentation comes from glycolysis, which produces a net of only 2 ATP per glucose molecule. In contrast, aerobic cellular respiration produces about 36 ATP per glucose molecule. To meet the same ATP demand under anaerobic conditions as under aerobic conditions, a cell's rate of glycolysis and glucose utilization must increase nearly 20-fold.

The effect of gramicidin on oxidative phosphorylation: Sort the labels into the correct bin according to the effect that gramicidin would have on each process.

remains the same: proton pumping rate, electron transport rate, rate of oxygen uptake decreases (or goes to zero): rate of ATP synthesis, size of the proton gradient Gramicidin causes membranes to become very leaky to protons, so that a proton gradient cannot be maintained and ATP synthesis stops. However, the leakiness of the membrane has no effect on the ability of electron transport to pump protons. Thus, the rates of proton pumping, electron transport, and oxygen uptake remain unchanged.

The coupled stages of cellular respiration: The four stages of cellular respiration do not function independently. Instead, they are coupled together because one or more outputs from one stage functions as an input to another stage. The coupling works in both directions, as indicated by the arrows in the diagram below. In this activity, you will identify the compounds that couple the stages of cellular respiration. Drag the labels on the left onto the diagram to identify the compounds that couple each stage. Labels may be used once, more than once, or not at all.

a. pyruvate b. NADH c. NAD+ d. NADH e. NAD+ The main coupling among the stages of cellular respiration is accomplished by NAD+ and NADH. In the first three stages, NAD+ accepts electrons from the oxidation of glucose, pyruvate, and acetyl CoA. The NADH produced in these redox reactions then gets oxidized during oxidative phosphorylation, regenerating the NAD+ needed for the earlier stages.

Suppose that a cell's demand for ATP suddenly exceeds its supply of ATP from cellular respiration. Which statement correctly describes how this increased demand would lead to an increased rate of ATP production? a. ATP levels would fall at first, increasing the inhibition of PFK and increasing the rate of ATP production. b. ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production. c. ATP levels would rise at first, increasing the inhibition of PFK and increasing the rate of ATP production. d. ATP levels would rise at first, decreasing the inhibition of PFK and increasing the rate of ATP production.

b. ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production. An increased demand for ATP by a cell will cause an initial decrease in the level of cellular ATP. Lower ATP decreases the inhibition of the PFK enzyme, thus increasing the rate of glycolysis, cellular respiration, and ATP production. It is the initial decrease in ATP levels that leads to an increase in ATP production.

Anaerobic conditions and acetyl CoA formation: Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. Which of these statements is the correct explanation for this observation? a. Oxygen is an input to acetyl CoA formation. b. In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration. c. ATP is needed to convert pyruvate to acetyl CoA. Without oxygen, no ATP can be made in oxidative phosphorylation. d. Oxygen is required to convert glucose to pyruvate in glycolysis. Without oxygen, no pyruvate can be made.

b. In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration. NAD+ couples oxidative phosphorylation to acetyl CoA formation. The NAD+ needed to oxidize pyruvate to acetyl CoA is produced during electron transport. Without O2, electron transport stops, and the oxidation of pyruvate to acetyl CoA also stops because of the lack of NAD+.

Why is the citric acid cycle a cyclic pathway rather than a linear pathway? a. More ATP is produced per CO2 released in cyclic processes than in linear processes. b. It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA. c. Redox reactions that simultaneously produce CO2 and NADH occur only in cyclic processes. d. Cyclic processes, such as the citric acid cycle, require a different mechanism of ATP synthesis than linear processes, such as glycolysis.

b. It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA. Although it is possible to oxidize the two-carbon acetyl group of acetyl CoA to two molecules of CO2, it is much more difficult than adding the acetyl group to a four-carbon acid to form a six-carbon acid (citrate). Citrate can then be oxidized sequentially to release two molecules of CO2.

In mitochondrial electron transport, what is the direct role of O2? In mitochondrial electron transport, what is the direct role of O2? a. to oxidize NADH and FADH2 from glycolysis, acetyl CoA formation, and the citric acid cycle b. to function as the final electron acceptor in the electron transport chain c. to provide the driving force for the production of a proton gradient d. to provide the driving force for the synthesis of ATP from ADP and Pi

b. to function as the final electron acceptor in the electron transport chain The only place that O2 participates in cellular respiration is at the end of the electron transport chain, as the final electron acceptor. Oxygen's high affinity for electrons ensures its success in this role. Its contributions to driving electron transport, forming a proton gradient, and synthesizing ATP are all indirect effects of its role as the terminal electron acceptor.

Which statement best explains why more ATP is made per molecule of NADH than per molecule of FADH2? Which statement best explains why more ATP is made per molecule of NADH than per molecule of FADH2? a. There is more NADH than FADH2 made for every glucose that enters cellular respiration. b. FADH2 is made only in the citric acid cycle while NADH is made in glycolysis, acetyl CoA formation, and the citric acid cycle. c. The H+ gradient made from electron transport using NADH is located in a different part of the mitochondrion than the H+ gradient made using FADH2. d. Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor. e. It takes more energy to make ATP from ADP and Pi using FADH2 than using NADH.

d. Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor. Electrons derived from the oxidation of FADH2 enter the electron transport chain at Complex II, farther down the chain than electrons from NADH (which enter at Complex I). This results in fewer H+ ions being pumped across the membrane for FADH2 compared to NADH, as this diagram shows. Thus, more ATP can be produced per NADH than FADH2.

What are the not inputs or outputs of oxidative phosphorylation?

glucose, coenzyme A, acetyl CoA, pyruvate, CO2