Mastering Chapter 9: Cellular Respiration
The proximate (immediate) source of energy for oxidative phosphorylation is...
...kinetic energy that is released as hydrogen ions diffuse down their concentration gradient.
For each glucose that enters glycolysis, ________ acetyl CoA enter the citric acid cycle.
2
Structure A is _____________.
ATP synthase. The purpose of ATP synthase is to phosphorylate ADP>
In the citric acid cycle, pyruvate is oxidized to __________.
CO2
In the citric acid cycle, FAD is reduced to ______________.
FADH2
Which of these is NOT a product of glycolysis?
FADH2. That is a product of the citric acid cycle.
What process is not apart of the cellular respiration pathway that produces large amounts of ATP in a cell?
Fermentation. This is an alternate pathway used when oxygen levels are low.
Which molecule is metabolized in a cell to produce energy "currency" in the form of ATP?
Glucose
What molecules belong in space A and B?
Glucose and oxygen. Photosynthesis produces glucose and releases oxygen into the atmosphere.
What process occurs in Box A?
Glycolysis. It occurs in the cytosol and turns glucose into a 2 pyruvates.
What organelle is indicated by the letter C?
Mitochondrion, the site of cellular respiration.
______________ is the compound that functions as the electron acceptor in glycolysis.
NAD+
Which of the following statements best describes what happens to a molecule of NAD+ when it gains a hydrogen atom?
NAD+ becomes reduced
In the citric acid cycle, NAD+ is reduced to ____________.
NADH
he reduced form of the electron acceptor in glycolysis is ____________.
NADH
What are the reactants in anaerobic reduction of pyruvate during lactic acid fermentation?
NADH and pyruvate
What molecule is indicated by the letter D?
Oxygen. I is the final electron acceptor 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.
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.
In mitochondrial electron transport, wat is the direct role of O2?
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.
What is the product of pyruvate metabolism by aerobic oxidation?
acetyl CoA
What is the product of pyruvate fermentation in yeast and bacteria?
ethanol
In glycolysis, the carbon-containing compound that functions as the electron donor is _______________.
glucose
What is the product of pyruvate fermentation in human muscle?
lactate
What are the products in anaerobic reduction of pyruvate during lactic acid fermentation?
lactate and NAD+
Citric Acid Cycle occurs in the __________________.
mitochondrial matrix Cellular respiration begins with glycolysis in the cytosol. Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes. Both acetyl CoA formation and the citric acid cycle take place in the matrix. The NADH and FADH2produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the inner mitochondrial membrane. The inner membrane provides the barrier that creates an H+ gradient during electron transport, which is used for ATP synthesis.
When a compound donates (loses) electrons, that compound becomes ________________. Such a compound is often referred to as an electron donor.
oxidized
When a glucose molecule loses a hydrogen atom in an oxidation-reduction reaction, the glucose molecule is __________________.
oxidized
Once the electron donor in glycolysis gives up its electrons, it is oxidized to a compound called _________________.
pyruvate
Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?
pyruvate, ATP, and NADH. ATP is the main product of cellular respiration that contains energy that can be used by other cellular processes. Some ATP is made in glycolysis. In addition, the NADH and pyruvate produced in glycolysis are used in subsequent steps of cellular respiration to make even more ATP.
In fermentation ____________ is reduced and ______________ is oxidized.
pyruvate; NADH The pyruvate from glycolysis is reduced to either lactate or ethanol, and NADH is oxidized to NAD+.
When a compound accepts (gains) electrons, that compound becomes _______________. Such a compound is often referred to as an electron acceptor.
reduced
In the citric acid cycle, ATP molecules are produced by...
substrate-level phosphorylation
In the citric acid cycle, ATP molecules are produced by...
substrate-level phosphorylation. A phosphate group is transferred form GTP to ADP.
In glycolysis, ATP molecules are produced by...
substrate-level phosphorylation. A phosphate group is transferred from glyceraldehyde phosphate to ADP.
During the electron transport, energy from ______________ is used to pump hydrogen ions into the _________________.
NADH and FADH2; intermembrane space. The energy released as electrons, which have been donated by NADH and FADH2, is passed along the electron transport chain and used to pump hydrogen ions into the intermembrane space.
True or false? The reactions that generate the largest amounts of ATP during cellular respiration take place in the mitochondria.
True. Glycolysis takes place in the cytosol, whereas the Krebs cycle and the electron transport chain, which generate the largest amounts of ATP during cellular respiration, take place in the mitochondria.
Glycolysis occurs in the _______________.
cytosol Cellular respiration begins with glycolysis in the cytosol. Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes. Both acetyl CoA formation and the citric acid cycle take place in the matrix. The NADH and FADH2produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the inner mitochondrial membrane. The inner membrane provides the barrier that creates an H+ gradient during electron transport, which is used for ATP synthesis.
Not an Input or Output of Glycolysis
Coenzyme A, O2, acetyl CoA, and CO2 In glycolysis, the six-carbon sugar glucose is converted to two molecules of pyruvate (three carbons each), with the net production of 2 ATP and 2 NADH per glucose molecule. There is no O2 uptake or CO2 release in glycolysis.
True or false? The potential energy in an ATP molecule is derived mainly from its three phosphate groups.
True. The three phosphate groups in an ATP molecule carry negative charges that strongly repel each other and give ATP a large amount of potential energy.
For each glucose that enters glycolysis, ________ acetyl CoA enter the citric acid cycle.
2. Each glucose produces two pyruvates, each of which is converted into acetyl CoA.
For each glucose that enters glycolysis, _______ NADH + H+ are produced by the citric acid cycle.
6. 3NADH + H+ are produced per each acetyl CoA that enters the citric acid cycle.
Which stage of glucose metabolism produces the most ATP?
Electron transport chain and chemiosmosis. They produce around 26 molecules of ATP.
In muscle cells, fermentation produces...
...lactate and NAD+
How many NADH are produced by glycolysis?
2
In glycolysis there is a net gain of ________ ATP.
2
Correct Statements
A bond must be broken between an organic molecule and phosphate before ATP can form. One of the substrates is a molecule derived from the breakdown of glucose. An enzyme is required in order for the reaction to occur.
The rate of cellular respiration is regulated by its major product, ATP, via feedback inhibition. As the diagram shows, high levels of ATP inhibit hhosphorfructokinase (PFK), an earl enzyme on glycolysis. As a result, the rate of cellular respiration, and this ATP production, decreases. Feedback inhibition enables cells to adjust their rate of cellular respiration to match their demands for ATP. Which statement correctly describes how this increased demand would leave to an increased rate of ATP production?
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.
Net Output of Oxidative Phosphorylation
ATP, NAD+, and water In oxidative phosphorylation, the NADH and FADH2 produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing O2 to water and recycling NAD+ and FAD back to the first three stages of cellular respiration. The electron transport reactions supply the energy to drive most of a cell's ATP production.
Net Output of the Citric Acid Cycle
ATP, NADH, CO2, and Coenzyme A In the citric acid cycle, the two carbons from the acetyl group of acetyl CoA are oxidized to two molecules of CO2, while several molecules of NAD+ are reduced to NADH and one molecule of FAD is reduced to FADH2. In addition, one molecule of ATP is produced.
Net Outputs of Glycolysis
ATP, NADH, and pyruvate In glycolysis, the six-carbon sugar glucose is converted to two molecules of pyruvate (three carbons each), with the net production of 2 ATP and 2 NADH per glucose molecule. There is no O2 uptake or CO2 release in glycolysis.
In glycolysis, what starts the process of glucose oxidation?
ATP. Some ATP energy is used to start the process.
Net Input of Citric Acid Cycle
Acetyl CoA, NAD+, and ADP In the citric acid cycle, the two carbons from the acetyl group of acetyl CoA are oxidized to two molecules of CO2, while several molecules of NAD+ are reduced to NADH and one molecule of FAD is reduced to FADH2. In addition, one molecule of ATP is produced.
What enters the citric acid cycle?
Acetyl CoA, but the coenzyme A is stripped leaving the 2 carbon acetyl.
Which of these is NOT a product of the citric acid cycle? a. acetyl CoA b. ATP c. FADH2 d. NADH + H+ e. CO2
Acetyl CoA, that is one of the reactants in the citric acid cycle.
Net Output of Acetyl CoA
Acetyle CoA, NADH, and CO2 In acetyl CoA formation, pyruvate (a product of glycolysis) is oxidized to acetyl CoA, with the reduction of NAD+ to NADH and the release of one molecule of CO2.
How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note you should NOT consider the effect on ATP synthesis in glycolysis or the citric acid cycle).
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.
Into which molecule are all the carbon atoms in glucose ultimately incorporated during cellular respiration?
CO2. All of the carbon atoms in glucose are incorporated into carbon dioxide: two molecules are formed as pyruvate is converted to acetyl CoA, and four molecules are formed during the Krebs cycle.
What molecules belong in spaces E and F?
Carbon dioxide and water. they are the by-products of cellular respiration.
Not an Input or Output of Oxidative Phosphorylation
Coenzyme A, Acetyl CoA, Pyruvate, Glucose, and CO2 In oxidative phosphorylation, the NADH and FADH2 produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing O2 to water and recycling NAD+ and FAD back to the first three stages of cellular respiration. The electron transport reactions supply the energy to drive most of a cell's ATP production.
NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce O2 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule. Why is more ATP made per molecule of NADH than per molecule of FADH2?
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.
Under anaerobic conditions (a lack of oxygen), glycolysis continues in most cells despite the fact that oxidative phosphorylation stops, and its production of NAD+ (which is needed as an input to glycolysis) also stops. The diagram illustrates the process of fermentation, which is used by many cells in the absence of oxygen. In fermentation, the NADH produced by glycolysis is used to reduce the pyruvate produced by glycolysis to either lactate or ethanol. Fermentation results in a net production of 2ATP pr glucose molecule. 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 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?
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 30 ATP per glucose molecule. To meet the ATP demand under anaerobic conditions as under aerobic conditions, a cell's rate of glycolysis and glucose utilization must increase about 15-fold.
Net Inputs of Glycolysis
Glucose, NAD+, and ADP In glycolysis, the six-carbon sugar glucose is converted to two molecules of pyruvate (three carbons each), with the net production of 2 ATP and 2 NADH per glucose molecule. There is no O2 uptake or CO2 release in glycolysis.
Not an Input or Output of Acetyl CoA
Glucose, O2, ADP, and ATP In acetyl CoA formation, pyruvate (a product of glycolysis) is oxidized to acetyl CoA, with the reduction of NAD+ to NADH and the release of one molecule of CO2.
Which step of the cellular respiration pathway can take place in the absence of oxygen?
Glycolysis. It can take place in the absence of oxygen; its product, pyruvate, enters the cellular respiration pathway or undergoes fermentation depending on the availability of oxygen.
Under anaerobic conditions (lack of oxygen), the conversion pyruvate to acetyl CoA stops. What statement explains this observation?
In the Adsense 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+.
In the oxidation of pyruvate to acetyl coA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms - in acetate - to CO2 requires a complex, eight step pathway - the citric acid cycle. Consider four possible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction.
It is easier o 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.
Which of the following statements about the electron transport chain is true? a. The electron transport chain is the first step in cellular respiration. b. Water is the last electron acceptor. c. NADH and FADH2 donate their electrons to the chain. d. Electrons gain energy as they move down the chain.
NADH and FADH2 donate their electrons to the chain. Electrons lose energy as they move down the chain, and this energy is used to create a proton gradient that drives the synthesis of ATP.
Net Input of Oxidative Phosphorylation
NADH, ADP, and O2 In oxidative phosphorylation, the NADH and FADH2 produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing O2 to water and recycling NAD+ and FAD back to the first three stages of cellular respiration. The electron transport reactions supply the energy to drive most of a cell's ATP production.
Not an Input or Output of the Citric Acid Cycle
O2, Glucose, and Pyruvate In the citric acid cycle, the two carbons from the acetyl group of acetyl CoA are oxidized to two molecules of CO2, while several molecules of NAD+ are reduced to NADH and one molecule of FAD is reduced to FADH2. In addition, one molecule of ATP is produced.
In cellular respiration, the most ATP molecules are produced by...
Oxidative phosphorylation. This process utilizes energy released by the electron transport chain.
The final electron acceptor of cellular respiration is _____________.
Oxygen. It is combined with electrons and hydrogen to form water.
Net Input of Acetyl CoA
Pyruvate, NAD+, and Coenzyme A In acetyl CoA formation, pyruvate (a product of glycolysis) is oxidized to acetyl CoA, with the reduction of NAD+ to NADH and the release of one molecule of CO2.
When the protein is integrated into a membrane, an H+ channel forms and the membrane becomes very permeable to protons (H+ ions). Of gramicidin is added to an actively respiring muscle cell, how would it affect the rates of electron transport, proton pumping, and ATP synthesis in oxidative phosphorylation? Assume that gramicidin does not affect the production of NADH and FADH2 during the early stages of cellular respiration).
Remains the same: proton pumping rate, electron transport rate, and rate of oxygen uptake. Decreases or goes to zero: size of the proton gradient and the rate of ATP synthesis. Increases: nothing 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.
What process occurs within Box B?
The citric acid cycle. This is where electrons are transferred to NADH and FADH2.
Incorrect Statements
The enzymes involved in AP synthesis must be attached to a membrane to produce ATP. The phosphate group added to ADP to make ATP comes from free inorganic phosphate ions.
Oxidative Phosphorylation occurs in the ___________________.
inner mitochondrial membrane Cellular respiration begins with glycolysis in the cytosol. Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes. Both acetyl CoA formation and the citric acid cycle take place in the matrix. The NADH and FADH2produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the inner mitochondrial membrane. The inner membrane provides the barrier that creates an H+ gradient during electron transport, which is used for ATP synthesis.
Acetyl CoA formation occurs in the _______________.
mitochondrial matrix Cellular respiration begins with glycolysis in the cytosol. Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes. Both acetyl CoA formation and the citric acid cycle take place in the matrix. The NADH and FADH2produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the inner mitochondrial membrane. The inner membrane provides the barrier that creates an H+ gradient during electron transport, which is used for ATP synthesis.
What process occurs in structure H?
photosynthesis