ETC

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Questions and Answers

What is the primary function of the electron transport chain described?

To convert free energy into heat for cellular processes

To transfer electrons through a series of proteins (correct)

To facilitate the uptake of oxygen in the mitochondria

To generate ATP directly from glucose metabolism

What role do cytochromes play in the electron transport chain?

They act as electron carriers that contain iron atoms (correct)

They enhance the flow of protons across the mitochondrial membrane

They convert oxygen to carbon dioxide during electron transport

They directly produce ATP when electrons are passed through them

What happens to the energy released during the electron transport chain process?

It is stored as chemical energy in glucose molecules

It is lost as heat and does not contribute to energy production

It is broken down into smaller, manageable amounts (correct)

It is released in large amounts to power cellular activities

Which statement is true regarding the ATP generation in the electron transport chain?

ATP generation occurs indirectly through subsequent processes Signup and view all the answers

What is the final electron acceptor in the electron transport chain?

Oxygen (O2) Signup and view all the answers

What is the primary purpose of the electron-transport chain in relation to NADH?

Transfers electrons to O2 while generating ATP through oxidative phosphorylation Signup and view all the answers

How many moles of ATP are typically produced from the oxidation of one NADH?

3 moles Signup and view all the answers

What factor increases with the protein complexes in the electron-transport chain?

The affinity for electrons Signup and view all the answers

What is the thermodynamic efficiency of oxidative phosphorylation under standard conditions?

42% Signup and view all the answers

How is the free energy change during oxidative phosphorylation described?

It is fragmented into smaller packets that couple with ATP synthesis Signup and view all the answers

What is the role of CoQH2 in the Q cycle?

Transferring electrons to one-electron acceptors Signup and view all the answers

How many protons are pumped into the intermembrane space during the Q cycle process?

Four protons Signup and view all the answers

What is the significance of having two different binding sites for Q in complex III?

It facilitates different electron transfer paths Signup and view all the answers

What occurs to the protons as they are pumped into the intermembrane space?

They contribute to the pH gradient Signup and view all the answers

What is the consequence of the electrons transferred from CoQH2 during the Q cycle?

They create a potential energy gradient Signup and view all the answers

What role does cytochrome c play in cellular respiration?

It is a mobile electron carrier that transports electrons. Signup and view all the answers

Which statement is true about the structure of cytochrome c?

It is covalently linked to the protein via two sulfur atoms. Signup and view all the answers

What is the function of the vinyl group in cytochromes?

It is identical in all cytochrome variants. Signup and view all the answers

What type of bonds link the heme group to cytochrome c?

Covalent bonds via sulfur atoms. Signup and view all the answers

Which compound does cytochrome c transport electrons from?

Ubiquinone. Signup and view all the answers

What is characterized by the specific absorption bands a, b, and g in cytochrome c?

Porphyrin rings. Signup and view all the answers

During the electron transport process involving cytochrome c, what state does it carry electrons in?

Reduced state. Signup and view all the answers

Which of these elements undergoes oxidation-reduction with one electron in cytochrome c?

Iron. Signup and view all the answers

What happens to proton influx during rest and decreased ATP use?

Proton influx decreases. Signup and view all the answers

Which molecules cannot be oxidized rapidly in the electron-transport chain when their levels build up?

NADH and FADH2 Signup and view all the answers

How much maximum ATP yield can be generated from one molecule of glucose during cellular respiration?

About 30 or 32 ATP Signup and view all the answers

What role do uncouplers play in oxidative phosphorylation?

They dissipate the proton gradient. Signup and view all the answers

Which stage of cellular respiration produces the least ATP directly?

Glycolysis Signup and view all the answers

What effect does a decreased electrochemical gradient have on the electron-transport chain?

It slows down the electron transport. Signup and view all the answers

Which of the following is NOT a product of glycolysis?

Acetyl CoA Signup and view all the answers

Which process primarily occurs in the mitochondrion during cellular respiration?

Oxidative phosphorylation Signup and view all the answers

What is the primary purpose of thermogenin in brown fat mitochondria?

To allow protons to return to the matrix and generate heat Signup and view all the answers

In cold-adapted mammals, which hormone binds to cells to initiate the process of nonshivering thermogenesis?

Norepinephrine Signup and view all the answers

Which process does the activation of protein kinase A (PKA) influence in brown fat cells?

Lipolysis of triacylglycerols Signup and view all the answers

What occurs as a result of the increase in cAMP levels triggered by norepinephrine?

Activation of adenylate cyclase Signup and view all the answers

How does brown fat help maintain the body temperature of newborn mammals lacking fur?

By generating heat through nonshivering thermogenesis Signup and view all the answers

What is the role of triacylglycerol lipase in brown fat metabolism?

To hydrolyze triacylglycerols into free fatty acids Signup and view all the answers

What is a unique characteristic of brown fat cells compared to white fat cells?

Brown fat cells are more vascularized Signup and view all the answers

What is the significance of the cytochromes present in the mitochondria of brown fat cells?

They provide the brown color and facilitate heat generation. Signup and view all the answers

Study Notes

Electron Transport and Oxidative Phosphorylation

Electron transport and oxidative phosphorylation occur in the mitochondria.
The outer mitochondrial membrane and the inner mitochondrial membrane are shown.
The location of proteins complexes I, III, IV, and V are shown embedded in the inner mitochondrial membrane.
Protons (H+) move from the matrix to the intermembrane space.
Oxygen (O2) is the final electron acceptor in the electron transport chain.
Water (H2O) is formed as a product.
ADP and phosphate (Pi) are used to form ATP.

Citric Acid Cycle

The citric acid cycle (also called the Krebs cycle) is a series of reactions in the mitochondria.
Key molecules involved include Acetyl CoA, oxaloacetate, malate, citrate, isocitrate, α-ketoglutarate, fumarate, and succinate.
NADH and FADH2 are produced, carrying high-energy electrons to the electron transport chain.
CO2 is released as a waste product.
ATP is produced via substrate-level phosphorylation.

ATP Yield Per Glucose Molecule

Glycolysis in the cytoplasm produces 2 ATP.
Pyruvate oxidation yields 2 NADH.
The citric acid cycle produces 2 ATP, 6 NADH, and 2 FADH2.
In the electron transport chain, oxidative phosphorylation generates 26-28 ATP.
The maximum ATP yield per glucose molecule is 30 or 32 ATP.

Key Questions of the Lecture

Electron transport and oxidative phosphorylation occur in the mitochondria.
Reduction potentials are used to determine free energy changes in redox reactions.
The electron transport chain is organized in a specific order with protein complexes.
Cytosolic NADH is transported into the mitochondria.
A proton gradient drives ATP synthesis.

The Fate of Electrons Removed from Glucose

Glucose oxidation occurs by molecular oxygen (O2).
In the first half-reaction, glucose carbon atoms are oxidized.
In the second half-reaction, molecular oxygen is reduced.
The 12 electron pairs involved aren't transferred directly to O2.
Coenzymes (NAD+ and FAD) are involved; 10 NADH and 2 FADH2 are formed.
These coenzymes become oxidized in the electron transport chain.

Mitochondrial Anatomy

Mitochondria have an outer membrane, inner membrane, cristae, and matrix.
The inner membrane is highly folded into cristae.
Heart muscle cells have densely packed cristae.
Liver cells have mitochondria with more sparsely distributed cristae.

The Malate-Aspartate Shuttle

Cytosolic NADH electrons are transported into the mitochondrial matrix.
Malate dehydrogenase and aspartate aminotransferase are involved.
This shuttle regenerates cytosolic oxaloacetate.

The Glycerophosphate Shuttle

Cytosolic NADH electrons are transported to the mitochondrial electron transport chain.
Glycerol-3-phosphate dehydrogenase is involved, transferring electrons to FAD.
This shuttle produces FADH2, which enters the electron transport chain.

ATP-ADP Translocase

ATP/ADP translocase is a key protein for transporting ATP and ADP across the inner mitochondrial membrane.
The process moves one negative charge out of the matrix.
ATP transport is favored, because of the electrochemical potential.

The Respiratory Chain for Oxidative Phosphorylation

Electrons are transferred from NADH/FADH2 to the electron-transport chain.
O2 is the final electron acceptor.
Water is formed as a product.
ATP is synthesized through chemiosmosis.

Concept of the Electron Transport Chain

The electron transport chain is a series of electron carriers that transfer electrons from NADH and FADH2 to O2 in a stepwise manner.
Each step releases smaller amounts of energy, rather than a single large burst of energy, which would be damaging to the cell.

Measurements of Redox Potentials

Redox reactions involve the transfer of electrons.
Reduction potentials (E°) quantify the tendency for a compound to gain electrons.
Standard reduction potentials (E°) measure the tendency of a molecule to be reduced compared to another.
Free energy change (ΔG°) is related to the difference in reduction potentials.

Biochemical Half Reactions

Half-reactions are parts of redox reactions.
Positive E° indicates a stronger oxidizing agent.
Negative E° indicates a stronger reducing agent.
High E° suggests that there is a high tendency for the compound to accept electrons.

NADH Oxidation

NADH oxidation is a highly exergonic reaction
Electron transfer from NADH to O2 releases a large amount of energy.
The oxidation of NADH to NAD is coupled with ATP synthesis.

Complex I (NADH Dehydrogenase)

Complex I is a large multi-subunit protein that receives electrons from NADH.
Flavin mononucleotide (FMN) and iron-sulfur clusters are components.

Complex II (Succinate-Coenzyme Q Oxidoreductase)

Complex II is part of the citric acid cycle.
Also receives electrons from succinate, which are transferred to CoQ (Ubiquinone).
It does not pump protons across the inner mitochondrial membrane.

Complex III (Cytochrome bc₁ Complex)

Complex III receives electrons from CoQ and passes them on to cytochrome c.
The Q cycle is involved in electron transfer.
Proton pumping occurs across the inner mitochondrial membrane.

Complex IV (Cytochrome c Oxidase)

Complex IV receives electrons from cytochrome c and transfers them to oxygen (O2).
Water is formed as a product; four protons are pumped across the inner mitochondrial membrane.

The Electron Jump in Complex IV

Redox centers participate in electron transfer in complex IV
Electrons move from cytochrome c to oxygen (O2).
CuA and CuB centers are involved in the process.

Coupling of Electron Transport and ATP Synthesis

Proton pumping across the inner mitochondrial membrane is driven by electron transport.
A proton gradient created.
This gradient's energy is subsequently used in ATP synthesis

The Chemiosmotic Hypothesis

Peter Mitchell's hypothesis that maintains that protons are pumped from the matrix into the intermembrane space.
This establishes an electrochemical potential.
ATP synthesis is fueled by the return of the protons to the matrix.

Structure and Mechanism of Molecular Motors

Molecular motors, like the F₁F₀-ATP synthase, have different conformations.
Protein rotation is a crucial step in ATP formation.

Binding-Change Mechanism in the F₀F₁ ATP Synthase

The process of ATP formation from ADP and P_i is described.
Rotations within the enzyme's structure are crucial.
Conformational changes for binding of ADP and Pi, the synthesis of ATP, and the release of ATP are discussed.

Regulation Through Coupling

ATP, ADP, and phosphate (Pi) concentration regulates the rate of electron transport and ATP production.
The electron transport chain rate and cellular respiration rate are dependent on these factors.

Uncoupling of Oxidative Phosphorylation in Brown Fat Mitochondria

Brown fat mitochondria contain UCP (uncoupling protein).
UCP dissipates the proton gradient, generating heat (nonshivering thermogenesis)
Energy from the gradient is released as heat.
Norepinephrine regulates electron transport in brown fat mitochondria.

Brown Fat Story

Brown fat is a specific type of adipose tissue found in mammals, helping with nonshivering thermogenesis.
Its role in maintaining body temperature, particularly in newborns and hibernating animals.
UCP (uncoupling protein) is a central component of brown fat metabolism.

The Versatility of Catabolism

Catabolism encompasses the breakdown of proteins, carbohydrates, and fats.
These substances can all be broken down to the citric acid cycle intermediate, acetyl coA.

Quiz Questions and Answers

Questions regarding components of respiratory chain complexes, and their involved electron transfer mechanisms (one or two-electron steps) were asked and answered.
The complex I-IV complexes of electron transfer were questioned and the roles explained in generating a proton gradient across the inner mitochondrial membrane.
The components of the proton-motive force (PMF) were queried.

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Test your knowledge on the electron transport chain with this quiz. Explore topics including the function of cytochromes, ATP generation, and the roles of CoQH2 and NADH. Perfect for biochemistry students looking to reinforce their understanding of cellular respiration.

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