Biology Lecture 10: Electron Transport and ATP Synthesis

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Questions and Answers

How many molecules of ATP does the average adult human synthesize per second?

10^20

10^19

10^18

10^21 (correct)

What is the primary location of electron transport proteins in eukaryotic cells?

Cytosol

Outer mitochondrial membrane

Endoplasmic reticulum

Inner mitochondrial membrane (correct)

What is the final step of the electron transport chain?

Reduction of O2 to water (correct)

Reduction of NAD+ to NADH

Synthesis of ATP from ADP

Reduction of FAD to FADH2

How many moles of ATP are synthesized from the energy generated by the reoxidation of 1 mole of NADH?

2-3 Signup and view all the answers

How many dehydrogenation steps occur in the citric acid cycle?

4 Signup and view all the answers

What is the term for the process by which ATP is synthesized from the energy generated by the reoxidation of NADH and FADH2?

Oxidative phosphorylation Signup and view all the answers

What is the total number of moles of NAD+ reduced to NADH and FAD reduced to FADH2 per mole of glucose?

10 Signup and view all the answers

What is the approximate weight of ATP synthesized by the average adult human per day?

Their own body weight Signup and view all the answers

Where are the enzyme complexes that reoxidize reduced electron carriers located?

Inner mitochondrial membrane Signup and view all the answers

What is the energy gradient created by the proton pumping action of the enzyme complexes used for?

ATP synthesis Signup and view all the answers

What is the electron carrier that receives electrons from the oxidation of NADH and succinate?

Coenzyme Q Signup and view all the answers

What is the final electron acceptor in the respiratory chain?

Oxygen Signup and view all the answers

What is the direction of proton pumping by the enzyme complexes?

From the matrix to the intermembrane space Signup and view all the answers

What is the role of complex III in the respiratory chain?

Catalyzing the transfer of electrons from coenzyme Q to cytochrome c Signup and view all the answers

What is the process by which protons re-enter the mitochondrial matrix?

Through a specific channel in complex V Signup and view all the answers

What is the energy source that drives ATP synthesis?

Energy released from the exergonic reactions of the respiratory chain Signup and view all the answers

What is the direction of the subunit rotation driven by the passage of protons through channels in F0?

Counterclockwise Signup and view all the answers

What conformational change occurs in the T site after a 120° rotation of the subunit?

T site changes to an O site Signup and view all the answers

What is the role of the nickel-coated bead in the experimental system?

It binds to the oligohistidine sequence Signup and view all the answers

What is the purpose of using streptavidin in the experimental system?

To couple fluorescent-tagged actin to the subunit Signup and view all the answers

What is observed during fluorescent microscopic examination after the addition of ATP and its subsequent hydrolysis?

The actin molecule is rotating Signup and view all the answers

What is the basis of the model of proton-driven rotation of the c-ring of the ATP synthase component?

X-ray structure of the E. coli ATP synthase Signup and view all the answers

What is the result of the conformational change in the L site after a 120° rotation of the subunit?

The L site binds to ADP and Pi Signup and view all the answers

What is the result of the conformational change in the O site after a 120° rotation of the subunit?

The O site releases ADP and Pi Signup and view all the answers

What is the approximate number of moles of ATP synthesized from the complete oxidation of 1 mole of glucose?

30-32 Signup and view all the answers

What type of enzymes catalyze the oxidation of a substrate without incorporation of oxygen atoms into the product?

Oxidases Signup and view all the answers

What is the term for enzymes that incorporate oxygen atoms from O2 into the oxidized products?

Oxygenases Signup and view all the answers

What is the term for the class of enzymes that incorporate one atom from O2 into a product and reduce the other atom to water?

Monooxygenases Signup and view all the answers

Which of the following is an example of a dioxygenase enzyme?

Tryptophan 2,3-dioxygenase Signup and view all the answers

What is the term for the enzyme complex that catalyzes the first reaction in tryptophan catabolism?

Tryptophan 2,3-dioxygenase Signup and view all the answers

What is the cofactor used by D-Amino acid oxidases?

FAD Signup and view all the answers

What is the general term for enzymes that catalyze the oxidation of a substrate with the incorporation of oxygen atoms into the product?

Oxygenases Signup and view all the answers

What is the effect of adding an exogenous oxidizable substrate, such as glutamate, to carefully prepared coupled mitochondria?

It slightly stimulates respiration, but only in the presence of ADP + Pi. Signup and view all the answers

Why is oxygen uptake recorded in moles O, rather than moles O2?

Because one pair of electrons reduces one atom of oxygen, not one molecule of oxygen. Signup and view all the answers

What is the typical ratio of ATP to ADP in most aerobic cells?

4:1 to 10:1 Signup and view all the answers

What happens to respiration when ADP is depleted in a relaxed and well-nourished cell?

It decreases due to the depletion of ADP. Signup and view all the answers

What is the role of ADP in respiratory control?

It is a substrate for phosphorylation and stimulates respiration. Signup and view all the answers

What is the effect of adding ADP + Pi to carefully prepared coupled mitochondria?

It significantly stimulates respiration, as ADP is a substrate for phosphorylation. Signup and view all the answers

What is the purpose of using oligomycins in this context?

As antibiotics to treat bacterial infections. Signup and view all the answers

Why does oxygen uptake slow down after the initial stimulation by ADP + Pi?

Because all of the ADP + Pi has been converted to ATP. Signup and view all the answers

Study Notes

Electron Transport, Oxidative Phosphorylation, and Oxygen Metabolism

The average adult human synthesizes ATP at a rate of nearly 10^21 molecules per second, equivalent to producing their own weight in ATP every day.
Under aerobic conditions, six dehydrogenation steps (one in glycolysis, one in pyruvate dehydrogenase, and four in the citric acid cycle) collectively reduce 10 moles of NAD+ to NADH and 2 moles of FAD to FADH2 per mole of glucose.
Reoxidation of these reduced electron carriers in the process of cellular respiration generates most of the energy needed for ATP synthesis.
Oxidation of 1 mole of NADH by the respiratory chain provides sufficient energy for the synthesis of ~2.5 moles of ATP from ADP.

The Mitochondrion: Scene of the Action

In eukaryotic cells, NADH and FADH2 are reoxidized by electron transport proteins bound to the inner mitochondrial membrane.
A series of linked oxidation and reduction reactions occurs, with electrons being passed along a series of electron carriers—the electron transport chain.
The final step is the reduction of O2 to water.
The overall electron transport sequence is quite exergonic.
One pair of reducing equivalents, generated from 1 mole of NADH, suffices to drive the synthesis of between 2 and 3 moles of ATP from ADP and Pi by a process termed oxidative phosphorylation.

Electron Transport

Embedded within the inner mitochondrial membrane are the protein carriers that constitute the respiratory chain.
Complex I and complex II receive electrons from the oxidation of NADH and succinate, respectively, and pass them along to a lipid-soluble electron carrier, coenzyme Q, which moves freely in the membrane.
Complex III catalyzes the transfer of electrons from the reduced form of coenzyme Q to cytochrome c, a protein electron carrier that is also mobile within the intermembrane space.
Complex IV catalyzes the oxidation of cytochrome c, reducing O2 to water.
The energy released by these exergonic reactions creates a proton gradient across the inner membrane, with protons being pumped from the matrix into the intermembrane space.
Protons then re-enter the matrix through a specific channel in complex V, driving the endergonic synthesis of ATP from ADP and inorganic phosphate.

Oxidative Phosphorylation

The experimental system that permits observation of rotation in the F1 component of F1F0 ATP synthase involves immobilizing the complex on a nickel-coated bead and attaching it to a glass coverslip.
Fluorescence microscopic examination showed that, following the addition of ATP and its subsequent hydrolysis by the catalytic subunits, the actin molecule was rotating, which proved that the subunit itself was rotating.
Proton-driven rotation of the c-ring of the F1F0 ATP synthase has been demonstrated experimentally.

Respiratory Control

In most aerobic cells, the level of ATP exceeds that of ADP by 4- to 10-fold.
Respiratory control is a dependence of respiration on ADP as a substrate for phosphorylation.
If the energy demands on a cell cause ATP to be consumed at high rates, the resultant accumulation of ADP will stimulate respiration, with concomitant activation of ATP resynthesis.
Conversely, in a relaxed and well-nourished cell, ATP accumulates at the expense of ADP, and the depletion of ADP limits the rate of both electron transport and its own phosphorylation to ATP.

Oxygen as a Substrate for Other Metabolic Reactions

The term oxidase is applied to enzymes that catalyze the oxidation of a substrate without incorporation of oxygen atom into the product.
A two-electron oxidation is usually involved, so the oxygen is converted to H2O2.
Most oxidases utilize either a metal or a flavin coenzyme.
Oxygenases are enzymes that incorporate oxygen atoms from O2 into the oxidized products; there are two classes—monooxygenases and dioxygenases.
Monooxygenases, which incorporate one atom from O2 into a product and reduce the other atom to water, are widely distributed and are also called mixed-function oxidases.

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Description

Learn about the mitochondrion, electron transport, oxidative phosphorylation, and oxygen metabolism, as well as the role of glycolysis and citric acid cycle in ATP synthesis.