Chapter 9 - Cellular Respiration

For each glucose that enters glycolysis, _____ acetyl CoA enter the citric acid cycle.

2

The glucose molecule has a large quantity of energy in its ________.

C—H bonds

What kind of molecules serve as electron acceptors in cellular respiration?

molecules with low potential energy

________ is a product of glycolysis, pyruvate processing, and the citric acid cycle.

NADH

The oxygen consumed during cellular respiration is involved directly in which process or event?

accepting electrons at the end of the electron transport chain

Which of these is NOT a product of the citric acid cycle?

acetyl CoA

Structure A is _____.

ATP synthase

A substrate-level phosphorylation occurs in the citric acid cycle when _____.

GDP is phosphorylated to produce GTP

Which process does not occur within a mitochondrion in a eukaryotic cell?

Glycolysis

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.

The final electron acceptor of cellular respiration is _____.

oxygen

In the citric acid cycle, ATP molecules are produced by _____.

substrate-level phosphorylation

In fermentation _____ is reduced and _____ is oxidized.

pyruvate ... NADH

Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?

pyruvate, ATP, and NADH

In glycolysis, as in all the stages of cellular respiration, the transfer of electrons from electron donors to electron acceptors plays a critical role in the overall conversion of the energy in foods to energy in ATP. These reactions involving electron transfers are known as oxidation-reduction, or redox, reactions. Drag the words on the left to the appropriate blanks on the right to complete the sentences.

1. When a compound donates (loses) electrons, that compound becomes [oxidized]. Such a compound is often referred to as an electron donor. 2. When a compound accepts (gains) electrons, that compound becomes [reduced]. Such a compound is often referred to as an electron acceptor. 3. In glycolysis, the carbon-containing compound that functions as the electron donor is [glucose]. 4. Once the electron donor in glycolysis gives up its electrons, it is oxidized to a compound called [pyruvate]. 5. [NAD+] is the compound that functions as the electron acceptor in glycolysis. 6. The reduced form of the electron acceptor in glycolysis is [NADH].

Substrate-level phosphorylation accounts for approximately what percentage of the ATP formed by the reactions of glycolysis?

100 percent

Glycolysis is a series of ___ reactions that occurs in the _____ of cells.

10; cytoplasm

In glycolysis there is a net gain of _____ ATP.

2

How would anaerobic conditions (when no O2O2 is present) affect the rate of electron transport and ATPATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATPATP synthesis in glycolysis or the citric acid cycle.)

Both electron transport and ATP synthesis would stop.

Which of the following statements about cellular metabolism is FALSE?

Citric acid cycle activity is dependent solely on availability of substrate; otherwise it is unregulated.

Which of these is NOT a product of glycolysis?

FADH2

Why would fermentation alone not be sufficient to keep your cells alive?

Fermentation has a much lower yield of ATP than the ETC.

Which of the following correctly pairs the process with its inputs and outputs?

Pyruvate processing-Inputs: pyruvate, NAD+; Outputs: acetyl CoA, NADH, CO2

Which of these enters the citric acid cycle?

acetyl CoA

What is the term for metabolic pathways that release stored energy by breaking down complex molecules?

catabolic pathways

The proximate (immediate) source of energy for oxidative phosphorylation is _____.

kinetic energy that is released as hydrogen ions diffuse down their concentration gradient

The primary role of oxygen in cellular respiration is to _____.

act as an acceptor for electrons and hydrogen, forming water

Chemiosmotic ATP synthesis (oxidative phosphorylation) occurs in ________.

all respiring cells, both prokaryotic and eukaryotic, using either oxygen or other electron acceptors

What process occurs in Box A?

glycolysis

C6H12O6 (glucose) + 6 O2 → 6 CO2 + 6 H2O Where is most of the water in this reaction produced?

in the electron transport chain

Where does the citric acid cycle occur in eukaryotes?

in the matrix of mitochondria

In muscle cells, fermentation produces _____.

lactate and NAD+

The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction ________.

loses electrons and loses potential energy

During cellular respiration, acetyl CoA accumulates in which location?

mitochondrial matrix

Carbon dioxide (CO2) is released during which of the following stages of cellular respiration?

oxidation of pyruvate to acetyl CoA and the citric acid cycle

In cellular respiration, most ATP molecules are produced by _____.

oxidative phosphorylation

When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, the molecule becomes ________.

oxidized

During glycolysis, when each molecule of glucose is catabolized to two molecules of pyruvate, most of the potential energy contained in glucose is _____.

retained in the two pyruvates

In mitochondrial electron transport, what is the direct role of O2O2?

to function as the final electron acceptor in the electron transport chain

What is the major adaptive advantage of cellular respiration?

to produce adenosine triphosphate (ATP)

In glycolysis, for each molecule of glucose oxidized to pyruvate _____.

two molecules of ATP are used and four molecules of ATP are produced.

When the protein gramicidin is integrated into a membrane, an H+ channel forms and the membrane becomes very permeable to protons (H+ ions). If 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.) Sort the labels into the correct bin according to the effect that gramicidin would have on each process.

Remains the same = 1) Electron transport rate 2) Proton pumping rate 3) Rate of oxygen uptake Decreases (or goes to zero) = 1) Rate of ATP synthesis 2) Size of the proton gradient

For each glucose that enters glycolysis, _____ NADH + H+ are produced by the citric acid cycle.

6

How many NADH are produced by glycolysis?

2

What molecule is indicated by the letter D?

oxygen

In glycolysis, what starts the process of glucose oxidation?

ATP

Which electron carrier(s) function in the citric acid cycle?

NADH and FADH2

During electron transport, energy from _____ is used to pump hydrogen ions into the _____.

NADH and FADH2 ... intermembrane space

How many oxygen molecules (O2) are required each time a molecule of glucose (C6H12O6) is completely oxidized to carbon dioxide and water via aerobic respiration?

6

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. Drag the labels from the left (which represent numbers of carbon atoms) onto the diagram to identify the number of carbon atoms in each intermediate in acetyl CoA formation and the citric acid cycle. Labels may be used more than once.

A) 2 C B) 6 C C) 6 C D) 5 C E) 4 C F) 4 C G) 4 C H) 4 C I) 4 C

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 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+

At the end of cellular respiration, protons flow through a protein called ATP synthase, which drives the formation of __________________.

ATP from ADP and inorganic phosphate

The rate of cellular respiration is regulated by its major product, ATP, via feedback inhibition. As the diagram shows, high levels of ATP inhibit phosphofructokinase (PFK), an early enzyme in glycolysis. As a result, the rate of cellular respiration, and thus ATP production, decreases. Feedback inhibition enables cells to adjust their rate of cellular respiration to match their demand for ATP. 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?

ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production.

Which of the listed statements describes the results of the following reaction? C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy

C6H12O6 is oxidized and O2 is reduced.

The ATP that is generated in glycolysis is produced by substrate-level phosphorylation, a very different mechanism than the one used to produce ATP during oxidative phosphorylation. Phosphorylation reactions involve the addition of a phosphate group to another molecule. Sort the statements into the appropriate bin depending on whether or not they correctly describe some aspect of substrate-level phosphorylation in glycolysis.

Correct statements = 1) One of the substrates is a molecule derived from the breakdown of glucose. 2) A bond must be broken between an organic molecule and phosphate before ATP can form. 3) An enzyme is required in order for the reaction to occur. Incorrect statements = 1) The phosphate group added to ADP to make ATP comes from free inorganic phosphate ions. 2) The enzymes involved in ATP synthesis must be attached to a membrane to produce ATP.

NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce O2to 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.

Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor.

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 2 ATP per 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 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?

Glucose utilization would increase a lot.

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?

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.

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. Use your knowledge of the first three stages of cellular respiration to determine which explanation is correct.

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.

Which of the following correctly describes the fermentation pathway? Select all that apply.

It produces 2 ATP molecules. It synthesizes a variety of the products depending on an electron acceptor. It includes a reaction that reduces NAD+ to NADH.

Which of the following statements about NAD+ is true?

NAD+ is reduced to NADH during glycolysis, pyruvate oxidation, and the citric acid cycle.

After glucose is fully oxidized by glycolysis, pyruvate processing, and the citric acid cycle, where is most of its energy stored?

NADH

Following glycolysis and the citric acid cycle, but before the electron transport chain and oxidative phosphorylation, the carbon skeleton of glucose has been broken down to CO2 with some net gain of ATP. Most of the energy from the original glucose molecule at that point in the process, however, is in the form of ________.

NADH

In mitochondria, exergonic redox reactions _____.

provide the energy that establishes the proton gradient

In glycolysis, ATP molecules are produced by _____.

substrate-level phosphorylation

What process occurs within Box B?

the citric acid cycle