Cellular Respiration BIO 100

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The reaction A --> B + C + heat is released in a(n) _____ reaction.

exergonic

A(n) _____ reaction occurs spontaneously.

exergonic

Which of these reactions requires a net input of energy from its surroundings?

endergonic

In cells, what is usually the immediate source of energy for an endergonic reaction?

ATP

The reaction ADP + P --> ATP is a(n) _____ reaction.

endergonic

The energy for an endergonic reaction comes from a(n) _____ reaction.

exergonic

What is the fate of the phosphate group that is removed when ATP is converted to ADP?

It is acquired by a reactant in an endergonic reaction.

Select the INCORRECT association

enzyme ... protein
exergonic ... uphill
potential energy ... positional energy
x exergonic ... spontaneous
kinetic energy ... motion

What is energy coupling?

the use of energy released from an exergonic reaction to drive an endergonic reaction

Which term describes the degree to which an element attracts electrons?

Electronegativity.

Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other?

Anion and cation.

Which of the following statements is true of the bonds in a water molecule?

Oxygen holds electrons more tightly than hydrogen does, and the net charge is zero.

Which of the following statements is not true of most cellular redox reactions?

A hydrogen atom is transferred to the atom that loses an electron.

What kind of bond is formed when lithium and fluorine combine to form lithium fluoride?

ionic

Gaseous hydrogen burns in the presence of oxygen to form water:

2H2 + O2 → 2H2 O + energy

Which molecule is oxidized and what kind of bond is formed?

Hydrogen, polar.

A cell has enough available ATP to meet its needs for about 30 seconds. What is likely to happen when an athlete exhausts his or her ATP supply?

Catabolic processes are activated that generate more ATP.

Refer to the figure in the text. What characteristic of this molecule (ATP) is responsible for its high energy level?

the closely spaced negative charges associated with the phosphate groups

How many NADH are produced by glycolysis?

2

In glycolysis, ATP molecules are produced by _____.

substrate-level phosphorylation

Which of these is NOT a product of glycolysis?

NADH
ATP
pyruvate
x FADH2

In glycolysis, what starts the process of glucose oxidation?

ATP

In glycolysis there is a net gain of _____ ATP.

2

Which of these is an example of negative feedback?

As a blood clot begins to form, the process of its formation gets faster and faster.
After you eat, glucagon stimulates an increase in blood sugar levels.
After you eat, insulin stimulates the lowering of blood sugar levels.
The digestive enzyme pepsinogen is converted to pepsin by the action of hydrochloric acid; pepsin itself can then convert pepsinogen into pepsin.
Once labor begins, contractions increase in frequency and intensity.

In the phosphofructokinase molecule shown in the figure below, the active site has a much higher affinity for ATP than the regulatory site does. Which answer best summarizes what the consequences would be if the regulatory site had a much higher affinity for ATP than the active site did?

Glucose oxidation would be inhibited even if ATP were scarce in the cell.

Two ATP molecules are expended in the energy investment phase of glycolysis. Why is this energy needed to begin the process of glucose catabolism?

Some energy must be invested to make the glucose molecule unstable and begin the process of catabolism.

Canine phosphofructokinase (PFK) deficiency afflicts springer spaniels, affecting an estimated 10% of the breed. PFK is the glycolytic enzyme that phosphorylates fructose-1-phosphate and catalyzes the committed step in glycolysis. Given its critical role in glycolysis, one implication of the genetic defect resulting in PFK deficiency in dogs is _____.

an intolerance for exercise

Substrate-level phosphorylation occurs within a metabolic pathway where sufficient energy is released by a given chemical reaction to drive the synthesis of ATP from ADP and phosphate. In which of the following metabolic pathways is substrate-level phosphorylation exhibited?

in both glycolysis and the Krebs cycle

The reactions of pyruvate processing, the citric acid cycle, and the electron transport chain occur within the _____ in the cell.

mitochondria

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 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 these enters the citric acid cycle?

acetyl CoA

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

substrate-level phosphorylation

Following glycolysis and the Krebs 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

If you were to add one of the eight Krebs cycle intermediates to the culture medium of yeast growing in the laboratory, what do you think would happen to their rates of ATP and carbon dioxide production?

The rates of ATP production and carbon dioxide production would both increase.

What is the function of coenzyme A in the Krebs cycle?

It is the coenzyme of acetylation reactions.

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

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

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.

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.

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.

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.

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

in the electron transport chain

The energy of electron transport serves to move (translocate) protons to the outer mitochondrial compartment. How does this help the mitochondrion to produce energy?

The translocation of protons sets up the electrochemical gradient that drives ATP synthesis in the mitochondria.

The inner mitochondrial membrane normally _____.

is virtually impermeable to hydrogen ions (protons)

Fatty acids usually have an even number of carbons in their structures. They are catabolized by a process called beta-oxidation. The end products of the metabolic pathway are acetyl groups of acetyl CoA molecules. What is the most likely fate of the acetyl groups?

They directly enter the Krebs cycle.

In muscle cells, fermentation produces _____.

lactate and NAD+

In fermentation _____ is reduced and _____ is oxidized.

pyruvate ... NADH

Which molecule is metabolized in a cell to produce energy for performing work?

Glucose

True or false? The potential energy in an ATP molecule is derived mainly from its three phosphate groups.

True

Which process is not part of the cellular respiration pathway that produces large amounts of ATP in a cell?

Fermentation

Which step of the cellular respiration pathway can take place in the absence of oxygen?

Glycolysis

Into which molecule are all the carbon atoms in glucose ultimately incorporated during cellular respiration?

Carbon dioxide

Which of the following statements about the electron transport chain is true?

NADH and FADH2 donate their electrons to the chain.

Which stage of glucose metabolism produces the most ATP?

Electron transport and chemiosmosis

True or false? The reactions that generate the largest amounts of ATP during cellular respiration take place in the mitochondria

True

When ATP is hydrolyzed into ADP and inorganic phosphate, _____.

a large amount of energy is released

When one molecule gains an electron from another, the molecule that received the electron has been _____.

reduced

In cellular respiration, glucose is _____ and oxygen is _____.

oxidized, reduced

_____ is the three-carbon sugar that is produced as an end product of glycolysis.

Pyruvate

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

GDP is phosphorylated to produce GTP

The enzyme phosphofructokinase is the major regulatory enzyme of glycolysis. It catalyzes _____.

the phosphorylation of fructose 6-phosphate

How do allosteric regulation and competitive inhibition compare?

Competitive inhibition involves binding of a regulatory molecule to the active site; in allosteric regulation a regulatory molecule binds to a different location.

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

pyruvate, ATP, and NADH

The chemiosmotic hypothesis is an important concept in our understanding of cellular metabolism in general because _____.

it explains how ATP is synthesized by a proton motive force

Why is ATP production during cellular respiration characterized as indirect?

ATP is not produced directly by the ETC but instead via the proton gradient generated during electron transport through the ETC.

Why are fermentation reactions important for cells?

They regenerate NAD+ so that glycolysis can continue to operate.

What would happen to NADH levels in a cell in the first few seconds after a drug has poisoned the enzyme that converts acetyl CoA to citrate?

NADH levels would decrease.

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