Chapter 9
When is most of the adenosine triphosphate (ATP) in cellular respiration produced?
During the last steps, when the electron transport chain generates a proton gradient for adenosine triphosphate (ATP) synthase to use
Anaerobic Respiration (Fermentation)
Electron acceptor ≠ oxygen Less efficient than aerobic respiration Results in alternate end products
The enzyme that is most often targeted in the regulation of glycolysis is __________.
phosphofructokinase, the third enzyme in the pathway
Electron Transport Chain Molecules that oxidize NADH and FADH2
Most are proteins One is a lipid-soluble, non-protein called ubiquinone or coenzyme Q or "Q" They have different redox potentials Some accept only electrons; others accept electrons plus protons
Which of the following products of cellular respiration would accumulate if there were no final electron acceptor in the electron transport chain (ETC)?
NADH If there were no final electron acceptor, the ETC would no longer oxidize NADHNADH to NAD+NAD+, which would result in an accumulation of NADHNADH.
When a person loses weight, where do the carbon molecules from the fat end up?
They are converted into acetyl CoA, sent through the citric acid cycle, and released as carbon dioxide (CO2).
During the citric acid cycle FADH2 and NADH are produced. What purpose do these molecules serve in the electron transport chain (ETC)?
They serve as electron donors in the ETC. Both NADH and FADH2 are reduced molecules and serve as electron donors.
What is the purpose of fermentation?
Transferring electrons from NADH so glycolysis can continue
What is the primary function of the citric acid cycle?
Transferring high-energy electrons to NAD+ and FAD
Cellular respiration produces more ATPATP per mole of glucose than fermentation.
True
Cellular respiration produces more CO2CO2 per mole of glucose than fermentation.
True
Role of the ETC Energy released as electrons move through the ETC
Used to pump protons across the mitochondrial inner membrane into the intermembrane space Forms a strong electrochemical gradient
What is the purpose of the electron transport chain (ETC) in cellular respiration?
Using energy from electrons to drive the formation of a proton gradient
Alfred has drawn a flow chart to show a time sequence of four processes of cellular respiration. Which sequence of three labels is the best choice to finish his model?
glycolysis / pyruvate processing / citric acid cycle This sequence is the best choice for completing the model with the names of processes written in the correct order.
For each glucose that enters glycolysis, _____ NADH + H+ are produced by the citric acid cycle.
6 3 NADH + H+ are produced per each acetyl CoA that enters the citric acid cycle.
Per glucose molecule:
6 CO2—disposed of when you exhale 4 ATP—directly used as fuel 10 NADH 2 FADH2
Cellular Respiration Takes 4 Steps
1.Glycolysis 2.Pyruvate processing 3.Citric acid cycle 4.Electron transport and oxidative phosphorylation
lycolysis is a series of 10 chemical reactions that occur in the cytosol
1.Uses two ATP in the energy investment phase (reactions 1-5) 2.Energy payoff phase (reactions 6-10), NADH is made and ATP is produced by substrate-level phosphorylation 3.The net yield is two NADH, two ATP, and two pyruvate
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.
In glycolysis there is a net gain of _____ ATP.
2 It takes 2 ATP to produce 4 ATP.
Cellular respiration produces more NADH per mole of glucose than fermentation.
True
Why do biologists now think this amount of ATPATP per molecule of glucose is not achieved in cells?
A cell will not produce this much ATP, because the proton-motive force is used in other transport steps and because of other issues that may reduce the overall efficiency.
Which of these is NOT a product of glycolysis?
FADH2 FADH2 is a product of the citric acid cycle.
Cellular respiration produces more lactate per mole of glucose than fermentation.
False
Where in a plant cell does glycolysis take place?
In the cytosol
How are the core pathways of cellular respiration important to plants and animals?
The intermediates can be used for the synthesis of essential macromolecules.
What is Cellular Respiration?
The process organisms use to generate ATP (an energy storage molecule)
What stage of cellular respiration is also part of fermentation?
glycolysis In both cellular respiration and fermentation, glycolysis oxidizes glucose to produce pyruvate and ATPATP.
The proximate (immediate) source of energy for oxidative phosphorylation is _____.
kinetic energy that is released as hydrogen ions diffuse down their concentration gradient Concentration gradients are a form of potential energy.
In muscle cells, fermentation produces _____.
lactate and NAD+ These are the products of fermentation as it occurs in muscle cells.
electron trnasport chain (ETC)
occurs in the inner membrane of the mitochondrion
Most of the adenosine triphosphate (ATP) made during cellular respiration is generated by __________.
oxidative phosphorylation
In cellular respiration, most ATP molecules are produced by _____.
oxidative phosphorylation This process utilizes energy released by electron transport.
The final electron acceptor of cellular respiration is _____.
oxygen Oxygen is combined with electrons and hydrogen to form water.
In the citric acid cycle, ATP molecules are produced by _____.
substrate-level phosphorylation A phosphate group is transferred from GTP to ADP.
In glycolysis, ATP molecules are produced by _____.
substrate-level phosphorylation A phosphate group is transferred from glyceraldehyde phosphate to ADP.
For each molecule of glucose processed during glycolysis, the net yield is ____.
two molecules of NADH, two of ATP, and two of pyruvate Glycolysis begins by using molecules of ATP, but the net yield is positive.
How many NADH are produced by glycolysis?
2 Two NADH molecules are produced by glycolysis.
What is ATP synthase?
A complex that uses a proton gradient to drive the synthesis of adenosine triphosphate (ATP)
In glycolysis, what starts the process of glucose oxidation?
ATP Some ATP energy is used to start the process of glucose oxidation.
Where in the citric acid cycle does adenosine triphosphate (ATP) regulate enzyme activity?
Acetyl CoA + oxaloacetate → citrate
Citric Acid Cycle
Acetyl CoA is oxidized into two CO2 Oxaloacetate to citrate to oxaloacetate Two turns per glucose molecule Nets three NADH, one FADH2, and two ATP
Where in the citric acid cycle does adenosine triphosphate (ATP) regulate enzyme activity?
Alpha-ketoglutarate → succinyl CoA
Where does adenosine triphosphate (ATP) bind to phosphofructokinase?
At both the active site and the regulatory site, as a substrate and an activator, respectively
Where does fructose-6-phosphate bind to phosphofructokinase?
At the active site, as a substrate
Where do the bubbles in beer come from?
Carbon dioxide (CO2) released during alcohol fermentation
Can you identify whether each activity takes place in cellular respiration, in fermentation, or in both?
Cellular respiration only: pyruvate is oxidized. Fermentation only: pyruvate is reduced. Both cellular respiration and fermentation: ATP is produced. NAD+ is produced. NADH is produced. Glucose is oxidized.
ATP Synthesis
Driven by ATP synthase Protons flow through and turn rotor Conformation change of knob phosphorylates ADP Yields up to 25 ATP via oxidative phosphorylation
Cellular respiration produces more pyruvate per mole of glucose than fermentation.
False
How is the citric acid cycle regulated?
Feedback inhibition by adenosine triphosphate (ATP) and NADH
Which of the following is not part of cellular respiration?
Fermentation
Early estimates suggested that the oxidation of glucose via aerobic respiration would produce 38 ATP. Based on what you know of the theoretical yields of ATP from cellular respiration, show how this total was determined.
For each glucose molecule, 2 ATP are produced in glycolysis and 2 ATP are produced in the citric acid cycle via substrate-level phosphorylation. A total of 10 NADH and 2 FADH2 molecules are produced from glycolysis, pyruvate oxidation, and the citric acid cycle. If each NADH were to yield 3 ATP, and each FADH2 were to yield 2 ATP, then a total of 34 ATP would be produced via oxidative phosphorylation. Adding these totals would result in 38 ATP.
Maria has drawn a flow chart using stars to track electron carriers (NADH and FADH2) during cellular respiration, but she hasn't completed her model. If twelve electron carriers are delivered to the electron transport chain (ETC) per molecule of glucose, how many stars should she show being produced during glycolysis and pyruvate processing?
Glycolysis and pyruvate processing each produce two NADH molecules, so two stars should be drawn into the model for each process.
Where is pyruvate dehydrogenase located?
In the cytosol of prokaryotes and the mitochondrial matrix of eukaryotes
After the four steps of cellular respiration, where is most of the energy stored?
In the form of ATP
Where do plants carry out the latter stages of cellular respiration—citric acid cycle, electron transport chain, and oxidative phosphorylation?
In the mitochondria
Cellular Respiration and Metabolism Catabolic pathways
Involve the breakdown of molecules Often harvest stored chemical energy to produce ATP
Where in the citric acid cycle does NADH regulate enzyme activity?
Isocitrate → alpha-ketoglutarate
What happens to pyruvate in the mitochondria?
It is converted to acetyl CoA in the matrix.
Pyruvate, a three-carbon molecule, is processed into acetyl CoA, a two-carbon molecule. What happened to the missing carbon?
It is lost as carbon dioxide (CO2) One carbon of the three-carbon pyruvate becomes oxidized to CO2.
Pyruvate has three carbons, and acetyl CoA has two carbons from the pyruvate. Where does the third carbon go?
It is released as carbon dioxide (CO2).
People need oxygen to survive. What is the primary function of inhaled oxygen?
It is the final electron acceptor in cellular respiration.
During 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.
Glycolysis Regulation Feedback inhibition Phosphofructokinase Two binding sites for ATP
One bound = active enzyme Two bound = inhibited enzyme
Pyruvate processed by enzyme complex called pyruvate dehydrogenase
One of its carbons is oxidized to CO2 NADH is produced The remaining two-carbon unit is attached to coenzyme A, producing acetyl CoA
A home brewer sets up a container with grain,* water, and yeast. She opens the container twice per day to check the progress and gently stir the mixture. Assuming she had all of the essential ingredients in the proper amounts, why can't she make beer? *The hops flowers are added later and are not germane to this question.
Opening the container so frequently supplies the yeast with oxygen for cellular respiration; they never switch to fermentation. Stirring just makes it worse!
Which of the four macromolecules (nucleic acids, carbohydrates, fats, and proteins) enters the cellular respiration pathway furthest downstream from glycolysis?
Proteins
Doesn't Always Start With Sugar
Proteins, carbohydrates, and fats can all furnish substrates for cellular respiration
Cellular Respiration and Metabolism Anabolic pathways
Result in the synthesis of larger molecules from smaller components Often use energy in the form of ATP
A woman adopted a lifestyle with a healthier diet and more exercise. She is thrilled that these changes have led to healthy weight loss. Where did the extra pounds go?
She exhaled them in the form of carbon dioxide (CO2).
Which of these is NOT a product of the citric acid cycle?
acetyl CoA Acetyl CoA enters the citric acid cycle.
Which of these enters the citric acid cycle?
acetyl CoA Acetyl CoA is a reactant in the citric acid cycle.
The first enzyme in glycolysis __________.
adds a phosphate from adenosine triphosphate (ATP) to the carbon ring
Substrate-level phosphorylation involves ________.
an enzyme and adenosine triphosphate (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+.