Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis

Question 1

The electron transport chain is a collection of molecules embedded in the inner membrane of the mitochondrion in

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eukaryotic cells

Question 2

In prokaryotes, these molecules reside in the

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plasma membrane

Question 3

The folding of the inner membrane to form cristae increases its surface area, providing space for thousands of copies of each component of the electron transport chain in a

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mitochondrion.

Question 4

Most components of the chain are proteins, which exist in

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multiprotein complexes numbered I through IV

Question 5

Tightly bound to these proteins are ____________________, nonprotein components such as cofactors and coenzymes essential for the catalytic functions of certain enzymes.

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prosthetic groups

Question 6

During this electron transport, electron carriers alternate between ___________________ as they accept and then donate electrons.

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reduced and oxidized states

Question 7

Each component of the chain becomes reduced when it accepts electrons from its “uphill” neighbor, which has a lower affinity for

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electrons (in other words, is less electronegative)

Question 8

It then returns to its oxidized form as it passes electrons to its

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“downhill,” more electronegative neighbor.

Question 9

free energy change during electron transport. During glycolysis and the citric acid cycle, electrons from food molecules are transferred to NAD+ and FAD forming

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NADH and FADH2

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these electrons carriers bring electrons to the electron transport chain in the inner

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mitochondrial membrane

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there the energy of electrons is converted to a form that powers the synthesis of

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ATP

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the overall function of the electron transport chain is to

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receive electrons from NADH and FADH2 and move them through a series of redox reactions

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when the electrons are in the NADH and FADH2 molecules they have a relatively high energy level and they lose a little energy with each

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redox exchange

Question 14

the electron transport chain is made up of

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four protein complexes, a smaller cytochrome protein, and an organic molecular called ubiquinone or Q

Question 15

Electrons acquired from glucose by NAD+ during glycolysis and the citric acid cycle are transferred from NADH to the first molecule of the

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electron transport chain in complex I

Question 16

This molecule is a flavoprotein, so named because it has a prosthetic group called

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flavin mononucleotide (FMN).

Question 17

In the next redox reaction, the flavoprotein returns to its oxidized form as it passes electrons to an iron-sulfur protein ( Feּּ* S in complex I), one of a family of proteins with both

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iron and sulfur tightly bound.

Question 18

The iron-sulfur protein then passes the electrons to a compound called

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ubiquinone

Question 19

Most of the remaining electron carriers between ubiquinone and oxygen are proteins called

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cytochromes

Question 20

Their prosthetic group, called a _______________, has an iron atom that accepts and donates electrons.

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heme group

Question 21

The electron transport chain has several types of cytochromes, each named “cyt” with a letter and number to distinguish it as a different protein with a slightly different

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electron-carrying heme group.

Question 22

The last cytochrome of the chain, Cyt aּּᴈ, passes its electrons to oxygen, which is very

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electronegative.

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Each oxygen atom also picks up a pair of hydrogen ions (protons) from the aqueous solution, neutralizing the charge of the added electrons and forming

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water.

Question 24

Another source of electrons for the electron transport chain is FADH2 , the other reduced product of the

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citric acid cycle.

Question 25

FADH2 adds its electrons from within complex II, at a lower energy level than

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NADH does.

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The electron transport chain makes no

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ATP directl;ly

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How does the mitochondrion (or the plasma membrane in prokaryotes) couple this electron transport and energy release to ATP synthesis?

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a mechanism called chemiosmosis.

Question 28

Populating the inner membrane of the mitochondrion or the prokaryotic plasma membrane are many copies of a protein complex called ,

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ATP synthase, the enzyme that makes ATP from ADP and inorganic phosphate

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ATP synthase uses the energy of an existing ion gradient to power

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ATP synthesis.

Question 30

The power source for ATP synthase is a difference in the concentration of H+ on opposite sides of the

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inner mitochondrial membrane.

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This process, in which energy stored in the form of a hydrogen ion gradient across a membrane is used to drive cellular work such as the synthesis of ATP, is called

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chemiosmosis

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ATP synthase is a multisubunit complex with

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four main parts, each made up of multiple polypeptide

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Protons move one by one into binding sites on one of the parts (the rotor), causing it to spin in a way that catalyzes ATP production from

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ADP and inorganic phosphate

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Establishing the gradient is a major function of the electron transport chain, which is shown in its

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mitochondrial location

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The chain is an energy converter that uses the exergonic flow of electrons from NADH and FADH2 to pump H+ across the membrane, from the .

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mitochondrial matrix into the intermembrane space

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The H+ has a tendency to move back across the membrane, diffusing down its gradient. And the ATP synthases are the only sites that provide a route through the membrane for

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H+

Question 37

Researchers have found that certain members of the electron transport chain accept and release protons (H+) along with

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electrons

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In eukaryotic cells, the electron carriers are spatially arranged in the inner mitochondrial membrane in such a way that H+ is accepted from the mitochondrial matrix and deposited in the

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intermembrane space

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emphasizing the capacity of the gradient to perform work.

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proton-motive force

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The force drives H+ back across the membrane through the H+ channels provided by

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ATP synthases.

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is an energy-coupling mechanism that uses energy stored in the form of an gradient across a membrane to drive cellular work.

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chemiosmosis

Question 42

In mitochondria, the energy for gradient formation comes from exergonic redox reactions along the

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electron transport chain, and ATP synthesis is the work performed

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Chloroplasts use chemiosmosis to generate ATP during

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photosynthesis

Question 44

In these organelles, light (rather than chemical energy) drives both electron flow down an electron transport chain and the resulting

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H+ gradient formation

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Prokaryotes, as already mentioned, generate H+ gradients across their

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plasma membranes.

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They then tap the proton-motive force not only to make ATP inside the cell but also to rotate their flagella and to

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pump nutrients and waste products across the membrane

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respiration overall function:

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harvesting the energy of glucose for ATP synthesis.

Question 48

During respiration, most energy flows in this sequence:

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glucoseּּ → NADHּּ → electron transport chain ּּ→ proton motive ּּ→ ATP

Question 49

We can do some bookkeeping to calculate the ATP profit when cellular respiration oxidizes a molecule of glucose to

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six molecules of carbon dioxide

Question 50

The three main departments of this metabolic enterprise are

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glycolysis, pyruvate oxidation and the citric acid cycle, and the electron transport chain, which drives oxidative phosphorylation.

Question 51

The tally adds the 4 ATP produced directly by substrate-level phosphorylation during glycolysis and the citric acid cycle to the many more molecules of

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ATP generated by oxidative phosphorylation.

Question 52

Each NADH that transfers a pair of electrons from glucose to the electron transport chain contributes enough to the proton-motive force to generate a maximum of about

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3 ATP.

Question 53

There are three reasons we cannot state an exact number of ATP molecules generated by the breakdown of

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one molecule of glucose.

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First, phosphorylation and the redox reactions are not directly coupled to each other, so the ratio of the number of NADH molecules to the number of ATP molecules is not a

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whole number.

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Second, the ATP yield varies slightly depending on the type of shuttle used to transport electrons from the

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cytosol into the mitochondrion

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A third variable that reduces the yield of ATP is the use of the proton-motive force generated by the redox reactions of

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respiration to drive other kinds of work

Question 57

Recall that the complete oxidation of a mole of glucose releases

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686 kcal of energy under standard conditions ( ּּ∆G= -686 kcal/mol)

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Phosphorylation of ADP to form ATP stores at least

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7.3 kcal per mole of ATP.

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Therefore, the efficiency of respiration is

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7.3 kcal per mole of ATP times 32 moles of ATP per mole of glucose divided by 686 kcal per mole of glucose, which equals 0.34.

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Thus, about 34% of the potential chemical energy in glucose has been transferred to

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ATP;

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The rest of the energy stored in glucose is lost as

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heat