Cellular Respiration and Electron Transport

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Questions and Answers

What is the primary site of oxygen utilization in aerobic tissues?

In the TCA cycle

In the mitochondrial intermembrane space

In the electron transport chain (correct)

During the oxidation of NADH and FADH2

What is the number of reactions that produce NADH + H+ from NAD+ in the TCA cycle?

Two

Three

One (correct)

Five

Where does the oxidation of NADH and FADH2 produced in the TCA cycle occur?

On the inner mitochondrial membrane (correct)

In the cytosol

In the mitochondrial matrix

In the nucleus

What is the characteristic of the electron transport chain?

Increasing electron affinity and increasing redox potential Signup and view all the answers

What would be the effect of making the inner mitochondrial membrane freely permeable to protons?

NADH would build up Signup and view all the answers

Which of the following would occur if the electron transport chain were inhibited?

NADH would build up Signup and view all the answers

What is the product of the reaction catalysed by pyruvate dehydrogenase?

Acetyl-CoA and NADH Signup and view all the answers

What is the central role of acetyl-CoA in metabolism?

It is a key intermediate in the metabolism of glucose, fatty acids, and amino acids Signup and view all the answers

What is the purpose of the dehydrogenase enzymes in the TCA cycle?

To produce reduced cofactors such as NADH and FADH2 Signup and view all the answers

What is the metabolic importance of oxaloacetate?

It can be produced from pyruvate by the pyruvate carboxylase reaction and is a key component of the TCA cycle Signup and view all the answers

What is the role of the TCA cycle in biosynthesis?

It acts as a source of biosynthetic precursors, such as amino acids and haem Signup and view all the answers

What is the result of the metabolic events of the TCA cycle?

The conversion of acetyl-CoA into two molecules of CO2 Signup and view all the answers

What is another name for the pathway that involves the oxidation of acetyl CoA to CO2 and water?

Krebs cycle Signup and view all the answers

Where does the TCA cycle take place?

Mitochondrial matrix Signup and view all the answers

What is the energy yield of the TCA cycle?

12 ATP Signup and view all the answers

What is the function of citrate synthase?

To convert oxaloacetate and acetyl-CoA to citrate Signup and view all the answers

What is the byproduct of the conversion of α-ketoglutarate to succinyl-CoA?

GTP Signup and view all the answers

Which of the following is NOT a tissue where the TCA cycle takes place?

Red blood cells Signup and view all the answers

What is the purpose of the link reaction?

To convert pyruvate to acetyl-CoA Signup and view all the answers

Which enzyme is responsible for the conversion of fumarate to malate?

Fumarase Signup and view all the answers

What is the net result of the re-oxidation of NADH and FADH2 via the electron transport chain?

The synthesis of ATP Signup and view all the answers

Which of the following is an irreversible step in the TCA cycle?

The conversion of α-ketoglutarate to succinyl-CoA Signup and view all the answers

Which of the following electron carriers is responsible for accepting electrons from NADH in the electron transport chain?

Flavin cofactor Signup and view all the answers

What is the primary function of the electron transport chain in oxidative phosphorylation?

To pump protons across the mitochondrial inner membrane, creating a proton gradient Signup and view all the answers

How does the rate of electron transport affect the proton gradient and ATP synthesis?

An increase in electron transport rate increases the proton gradient and ATP synthesis Signup and view all the answers

What is the effect of uncouplers on the electron transport chain and ATP synthesis?

Uncouplers dissipate the proton gradient, decreasing ATP synthesis Signup and view all the answers

Which of the following is a characteristic of the electron transport chain in the mitochondrial inner membrane?

The electron transport chain is a series of protein complexes that pump protons across the membrane Signup and view all the answers

What is the role of the F0, F1-ATP synthase in oxidative phosphorylation?

To synthesise ATP from ADP and Pi using the energy from the proton gradient Signup and view all the answers

How does the level of ATP affect the rate of electron transport?

An increase in ATP level decreases the rate of electron transport Signup and view all the answers

What is the effect of inhibitors on the electron transport chain and ATP synthesis?

Inhibitors inhibit the electron transport chain and decrease ATP synthesis Signup and view all the answers

What is the role of the proton gradient in oxidative phosphorylation?

To drive ATP synthesis from ADP and Pi using the energy from the proton gradient Signup and view all the answers

What is the net ATP yield from the complete oxidation of one molecule of glucose?

32 ATP Signup and view all the answers

Study Notes

Aerobic Metabolism: The TCA Cycle and Oxidative Phosphorylation

In aerobic tissues, O2 utilization results from its reduction to H2O by cytochrome oxidase.
The TCA cycle (also known as Krebs cycle, Citric acid cycle, or Tricarboxylic acid cycle) is a common terminal pathway for the catabolism of sugars, fats, and amino acids.
The TCA cycle occurs in the mitochondrial matrix of all tissues with mitochondria, except for red blood cells and white muscle fibers.

TCA Cycle Reactions

The TCA cycle is a series of 8 reactions that convert acetyl-CoA into 2 molecules of CO2.
The cycle produces NADH and FADH2, which are used to generate ATP in the Electron Transport Chain.
The TCA cycle also produces GTP, which is used to generate ATP.
The reactions of the TCA cycle are:
- Condensation reaction: Citrate synthase catalyzes the formation of citrate from oxaloacetate and acetyl-CoA.
- Isomerisation: Aconitase catalyzes the conversion of citrate to isocitrate.
- First loss of CO2: Isocitrate dehydrogenase catalyzes the conversion of isocitrate to α-ketoglutarate.
- Second loss of CO2: α-Ketoglutarate dehydrogenase catalyzes the conversion of α-ketoglutarate to succinyl-CoA.
- Trapping thioester bond energy as GTP: Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate and GTP.
- Conversion of succinate to fumarate: Succinate dehydrogenase catalyzes the conversion of succinate to fumarate.
- Conversion of fumarate to malate: Fumarase catalyzes the conversion of fumarate to malate.
- Conversion of malate to oxaloacetate: Malate dehydrogenase catalyzes the conversion of malate to oxaloacetate.

Generation of ATP

The re-oxidation of NADH to NAD and FADH2 to FAD via the Electron Transport Chain results in the synthesis of ATP from ADP and Pi (Oxidative Phosphorylation).
The energy yields of the TCA cycle are:
- 3 enzyme reactions produce NADH and H+, yielding 3 x 2.5 ATP = 7.5 ATP.
- 1 enzyme reaction produces FADH2, yielding 1 x 1.5 ATP = 1.5 ATP.
- 1 enzyme reaction produces GTP, yielding 1 x 2 ATP = 2 ATP.
- Total ATP yield: 12 ATP (old numbers) or 10 ATP (new numbers).

Irreversibility of Key Stages

Three enzyme steps are highly exergonic and irreversible:
- Citrate synthase
- Isocitrate dehydrogenase
- α-Ketoglutarate dehydrogenase### Chemical Nature and Sequential Arrangement of Electron Carriers
Electron carriers in the mitochondrial inner membrane are organized in complexes that conserve energy from the reoxidation of NADH and FADH2 by pumping protons across the membrane.
The energy from the proton gradient is used for the synthesis of ATP from ADP by the F0, F1-ATP synthase.

Electron Transport Chain

The electron transport chain is a process for the transfer of H atoms to oxygen.
It takes place in the mitochondria and occurs in most tissues and cell types, except for red blood cells.
The function of the electron transport chain is to trap energy and phosphorylate ADP to produce ATP.
Components of the electron transport chain are "buried" in the inner mitochondrial membrane.
The electron transport chain involves the stepwise transfer of H atoms to O2, with the participation of electron carriers such as NADH, flavin cofactors, coenzyme Q, iron-sulfur proteins, and cytochrome proteins.

Electron Carriers

NADH is the reduced form of nicotinamide adenine dinucleotide, with a nicotinamide ring and a ribose molecule.
The electron transport chain involves the transfer of electrons from NADH to O2, resulting in the formation of water and the release of energy.

Complexes of the Electron Transport Chain

Complex I: NADH dehydrogenase, also known as NADH:ubiquinone oxidoreductase.
Complex III: cytochrome b-c1 complex, also known as cytochrome reductase.
Complex IV: cytochrome c oxidase, also known as cytochrome a3.
The electron transport chain is organized in these complexes, which work together to pump protons across the membrane and generate a proton gradient.

ATP Synthesis

The proton gradient is used to drive the synthesis of ATP from ADP by the F0, F1-ATP synthase.
The ATP synthase is a membrane-associated protein that uses the energy from the proton gradient to drive the phosphorylation of ADP.

Control of Electron Transport

The rate of electron transport is controlled by the levels of ADP and ATP, a process known as respiratory control or "tightly-coupled" oxidative phosphorylation.
Increased ADP levels increase the rate of O2 uptake, while increased ATP levels decrease O2 uptake.

Inhibitors and Uncouplers

Inhibitors of oxidative phosphorylation include CN, rotenone, and CO, which block the electron transport chain.
Uncouplers of oxidative phosphorylation include dinitrophenol (DNP) and thermogenin protein in brown adipose tissue, which disrupt the proton gradient and prevent ATP synthesis.

ATP Yield

The ATP yield from the complete oxidation of one molecule of glucose is 32 or 30 ATP, depending on the shuttle used to transfer NADH into the mitochondria.
The ATP yield from the oxidation of NADH is 2.5 ATP, while the ATP yield from the oxidation of FADH2 is 1.5 ATP.

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Description

Test your knowledge on cellular respiration, TCA cycle, and electron transport chain. Answer questions on the primary site of oxygen utilization, NADH production, and the effects of inhibiting the electron transport chain.