Chapters 8 and 9 Mastering Biology

In glycolysis, what starts the process of glucose oxidation?

ATP

What box would you draw an X through to trigger the onset of fermentation reactions?

O2

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

C—H bonds

_______ is the compound that functions as the electron acceptor in glycolysis.

NAD+

The reduced form of the electron acceptor in glycolysis is _______.

NADH

A newly developed insecticide compound steals high-energy electrons from FADH2 and NADH before they can bind to the electron transport chain. Why does this kill insects?

The ETC cannot establish a proton gradient to drive chemiosmotic production of ATP.

This animation below shows a metabolic pathway with three kinds of enzymes. Which enzyme comes second in the pathway?

The enzyme at the lower right.

You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme?

The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity.

What would you expect the ΔG values to be for the two steps in the uncoupled reaction.

The uncoupled reaction has a ΔG of about +1.3 kcal/mol

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

pyruvate, ATP, and NADH

When a compound accepts (gains) electrons, that compound becomes _______. Such a compound is often referred to as an electron acceptor.

reduced

How many NADH are produced by glycolysis?

2

In glycolysis there is a net gain of _____ ATP.

2

Which statement best summarizes the net production of ATP?

2 ATP (glycolysis) + 2 ATP (citric acid cycle) + 25 ATP (chemiosmosis) = 29 ATP produced per glucose molecule

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.

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down. What can you do to speed the reaction up again?

Add more substrate; it will outcompete the inhibitor and increase the reaction rate.

Which of these is an example of negative feedback?

After you eat, insulin stimulates the lowering of blood sugar levels.

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.)

Both electron transport and ATP synthesis would stop.

Which answer correctly associates a process in cellular respiration with (1) what goes in and (2) what comes out?

Citric acid cycle: (1) Acetyl CoA; (2) NADH, ATP (or GTP), FADH2,, and CO2

What molecule produced during the citric acid cycle feeds into the electron transport chain?

FADH2

Which of these is NOT a product of glycolysis?

FADH2

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. Which statement best explains why more ATP is 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.

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.

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

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. Drag the labels on the left to show the net redox reaction in acetyl CoA formation and the citric acid cycle. Note that two types of electron carriers are involved.

a. CO2 b. NADH c. FAD d. FADH2

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 competitive inhibitor competes with the substrate for the _______ on the enzyme.

active site

What molecule is produced in the citric acid cycle as a by-product of glucose oxidation and is considered a waste product?

carbon dioxide

A (n) ________ inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate.

competitive

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) An enzyme is required in order for the reaction to occur 2) A bond must be broken between an organic molecule and phosphate before ATP can form. 3) One of the substrate is a molecule derived from the breakdown go glucose 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.

When the noncompetivitve inhibitor is bonded to the enzyme, the shape of the _______ is distorted.

enzyme

True or false? If you used a radioactive label to trace the pathway of oxygen through cell respiration, the label would end in CO2.

false

In glycolysis, the carbon-containing compound that functions as the electron donor is _______.

glucose

Concept Map: How is the energy in glucose extracted for use in the cell?

glucose ENTERS glycolysis glycolysis RELEASES PYRUVATE TO pyruvate processing pyruvate processing RELEASES ACETYL-COA TO citric acid cycle citric acid cycle YIELDS 2ATP and CO2 citric acid cycle RELEASES NADH AND FADH2 TO electron transport chain and chemiosmosis electron transport chain and chemiosmosis YIELDS ~25ATP and H2O oxygen ENTERS electron transport chain and chemiosmosis

What process occurs in Box A?

glycolysis

Each of the four stages of cellular respiration occurs in a specific location inside or outside the mitochondria. These locations permit precise regulation and partitioning of cellular resources to optimize the utilization of cellular energy. Match each stage of cellular respiration with the cellular location in which it occurs. Labels may be used once, more than once, or not at all.

glycolysis -cytosol acetyl CoA formation - mitochondrial matrix citric acid cycle - mitochondrial matrix oxidative phosphorylation - inner mitochondrial membrane

Usually, a(n) _______ inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity.

irreversible

In the last stage of cellular respiration, oxidative phosphorylation, all of the reduced electron carriers produced in the previous stages are oxidized by oxygen via the electron transport chain. The energy from this oxidation is stored in a form that is used by most other energy-requiring reactions in cells. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of oxidative phosphorylation. Drag each compound to the appropriate bin. If a compound is not involved in oxidative phosphorylation, drag it to the "not input or output" bin. (Note that not all of the inputs and outputs of oxidative phosphorylation are listed.)

net input: O2, ADP, NADH net output: water, NAD+, ATP not input or output: CO2, glucose, coenzyme A, acetyl-CoA, pyruvate

In the citric acid cycle (also known as the Krebs cycle), acetyl CoA is completely oxidized. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of the citric acid cycle. Drag each compound to the appropriate bin. If a compound is not involved in the citric acid cycle, drag it to the "not input or output" bin. (Note that not all of the inputs and outputs of the citric acid cycle are included.)

net input: acetyl-CoA, NAD+, ADP net output: NADH, CO2, ATP, coenzyme A not input or output: glucose, O2, pyruvate

From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of glycolysis. Drag each compound to the appropriate bin. If the compound is not involved in glycolysis, drag it to the "not input or output" bin.

net input: glucose, NAD+, ADP net output: pyruvate, NADH, ATP not input or output: O2, CO2, coenzyme A, acetyl-CoA

In acetyl CoA formation, the carbon-containing compound from glycolysis is oxidized to produce acetyl CoA. From the following compounds involved in cellular respiration, choose those that are the net inputs and net outputs of acetyl CoA formation. Drag each compound to the appropriate bin. If a compound is not involved in acetyl CoA formation, drag it to the "not input or output" bin. (Note that not all of the inputs and outputs of acetyl CoA formation are included.)

net input: pyruvate, coenzyme A, NAD+ net output: CO2, NADH, acetyl-CoA not input or output: ATP, ADP, glucose, O2

A (n) _______ inhibitor binds to a site on the enzyme that is not the active site.

noncompetitive

When a compound donates (loses) electrons, that compound becomes _______. Such a compound is often referred to as an electron donor.

oxidized

What molecule is indicated by the letter D?

oxygen

Once the electron donor in glycolysis gives up its electrons, it is oxidized to a compound called _______.

pyruvate

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: proton pumping rate, electron transport rate, rate of oxygen uptake decreases (or goes to zero): rate of ATP synthesis, size of the proton gradient

Enzyme inhibitor disrupt normal interactions between an enzyme and its _______.

substrate

In glycolysis, ATP molecules are produced by _____.

substrate-level phosphorylation

If the hydrolysis of ATP releases 7.3 kcal of free energy, use the graph in this figure to estimate what you would expect the ΔG values to be for the coupled reaction.

tep 1 has a ΔG of about -3 kcal/mol and step 2 has a ΔG of about -3 kcal/mol

What process occurs in Box B?

the citric acid cycle

In mitochondrial electron transport, what is the direct role of O2?

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

True or false? If you used a radioactive label to trace the pathway of carbon through cell respiration, the label would begin in glucose and end in CO2.

true