Biochemistry Chapter on Oxidative Phosphorylation

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Questions and Answers

What is the primary function of ATP synthase in the electron transport chain?

To act as an uncoupling agent in oxidative phosphorylation

To transport electrons across the inner mitochondrial membrane

To form ATP by utilizing the energy from proton translocation (correct)

To generate heat by dissipating energy not trapped in ATP

What occurs to energy released in the electron transport chain if it is not trapped in ATP?

It is utilized in anabolic pathways throughout the body

It is stored as glycogen for later use

It is converted to FADH2 for further reactions

It is released in the form of body heat (correct)

Which subcomplex of ATP synthase is primarily involved in ATP production?

Fo subcomplex

F1 subcomplex (correct)

Gamma subunit

C protein subunits

Which of the following statements is true regarding the P-O ratios for NADH and FADH2?

The P-O ratio for NADH is 2.5, while for FADH2 it is 1.5 Signup and view all the answers

What is the role of the Fo subcomplex in ATP synthase?

It spans the mitochondrial membrane and acts as proton channels Signup and view all the answers

What is the significance of the glycerol-3-phosphate shuttle system?

It assists in transporting electrons to the electron transport chain Signup and view all the answers

Which component of ATP synthase is primarily responsible for the rotary motion during ATP synthesis?

Gamma subunit Signup and view all the answers

What characterizes the binding change mechanism of ATP synthesis?

It involves conformational changes in the beta subunits Signup and view all the answers

What occurs during the exergonic reaction A → B?

Energy is released as heat. Signup and view all the answers

What purpose does ATP serve in energy metabolism?

It traps released energy from exergonic reactions. Signup and view all the answers

Which bond in ATP is indicated by the squiggle symbol ~(E)?

High energy bond. Signup and view all the answers

What is the role of creatine phosphate in energy production?

It provides energy for phosphorylating ADP to ATP. Signup and view all the answers

Why is the reaction C → D not occurring simultaneously with A → B?

It is an endergonic reaction. Signup and view all the answers

What reaction exemplifies substrate level phosphorylation?

The cleavage of creatine phosphate. Signup and view all the answers

What happens to the energy released during the reaction A → B if it is not captured?

It dissipates as heat and increases entropy. Signup and view all the answers

How is ATP synthesized from ADP during the reaction involving creatine phosphate?

Through substrate level phosphorylation. Signup and view all the answers

What is the energy released when ATP is hydrolyzed to ADP and Pi?

-7.3 kJ/mol Signup and view all the answers

What role does pyrophosphate (PPi) play in a reaction involving AMP?

It makes the reaction irreversible. Signup and view all the answers

How much energy is released when AMP and PPi are completely hydrolyzed?

-12.3 kJ/mol Signup and view all the answers

What does substrate level phosphorylation directly involve?

The transfer of a phosphate group from a substrate to ADP. Signup and view all the answers

What is the primary source of energy generation in the body?

Oxidative phosphorylation. Signup and view all the answers

What is the change in Gibbs free energy (ΔGo’) for the reaction Glucose + Pi → Glucose 6-phosphate + H2O?

+13.8 kJ/mol Signup and view all the answers

What is the typical P-O ratio in oxidative phosphorylation?

1.5 or 2.5 Signup and view all the answers

Which enzyme is responsible for converting glucose to glucose 6-phosphate?

Hexokinase Signup and view all the answers

What primarily drives ATP formation in oxidative phosphorylation?

Electrons removed during substrate oxidation Signup and view all the answers

Which complexes in the electron transport chain pump protons to the intermembrane space?

Complexes I, III, and IV Signup and view all the answers

What theory explains the mechanism of oxidative phosphorylation?

Chemiosmotic coupling theory Signup and view all the answers

What is generated as a result of the proton pumping in the mitochondria?

Electrochemical potential Signup and view all the answers

Where do the protons re-enter the mitochondrial matrix during ATP formation?

Through ATP synthase (Complex V) Signup and view all the answers

Which of the following is NOT a source of NADH and FADH2 in metabolism?

Protein degradation Signup and view all the answers

Which statement about complex II in the electron transport chain is true?

It is not involved in proton translocation. Signup and view all the answers

What is the primary role of ATP synthase in oxidative phosphorylation?

To synthesize ATP by utilizing the proton gradient Signup and view all the answers

What does a negative ΔG indicate about a reaction?

The reaction proceeds spontaneously. Signup and view all the answers

What occurs when ΔG is zero?

The system is at equilibrium. Signup and view all the answers

Which statements correctly describe ΔGo?

It represents free energy change at 1.0 mol/L concentrations. Signup and view all the answers

How can endergonic reactions proceed?

With the coupling to an exergonic reaction. Signup and view all the answers

What is the relationship between exergonic and endergonic reactions?

Exergonic reactions can drive endergonic reactions. Signup and view all the answers

What characterizes a reaction with a high magnitude of ΔG when it is positive?

It requires a significant amount of energy to occur. Signup and view all the answers

When is a reaction considered isoergonic?

When the system is at equilibrium with ΔGo’ being zero. Signup and view all the answers

What does an endergonic reaction require?

Absorption of energy. Signup and view all the answers

Which statement is true about exergonic reactions?

They can occur spontaneously. Signup and view all the answers

What defines an exergonic reaction based on standard free energy change?

ΔGo’ is negative. Signup and view all the answers

Study Notes

Overview of Oxidative Phosphorylation

NADH and FADH2 are produced in multiple metabolic processes, including glycolysis, beta-oxidation of fatty acids, the TCA cycle, and other oxidative reactions.
Electrons transfer from NADH to O2 occurs in stages through large protein complexes embedded in the inner mitochondrial membrane.
Complexes I, III, and IV use the energy from electron transfer to pump protons to the intermembrane space.
The pumping of protons creates an electrochemical gradient or proton-motive force.
Protons re-enter the mitochondrial matrix through ATP synthase, causing ATP to be generated.
The P-O ratio for NADH is 2.5. This means 2.5 ATP molecules are produced per NADH molecule.
The P-O ratio for FADH2 is 1.5. This means 1.5 ATP molecules are produced per FADH2 molecule.

Chemiosmotic Coupling Theory

This theory explains how oxidative phosphorylation works.
Energy from oxidation of components in the electron transport chain is coupled to proton translocation across the inner mitochondrial membrane.

ATP Synthase (Complex V)

Functions as a rotary motor to form ATP.
Embedded in the inner mitochondrial membrane.
Composed of two subcomplexes:
Fo subcomplex: Contains a disk of C protein subunits, the gamma subunit attached to Fo and F1, and the oligomycin sensitivity conferring enzyme (OSCP).
F1 subcomplex: Contains three alpha subunits and three beta subunits.
Fo spans the membrane and serves as a proton channel.
F1's beta subunit is the site of ATP synthesis.

Electron Shuttle Systems

Two known shuttle systems:
Glycerol-3-phosphate shuttle system: Simpler system using glycerol-3-PO4+ dehydrogenase. Major shuttle system in the brain and myocytes. Uses FAD as a mitochondrial electron carrier with a P-O ratio of 1.5.
Malate-aspartate shuttle system: More complex system. Uses NAD as a mitochondrial electron carrier with a P-O ratio of 2.5.

ΔG: Change in Free Energy

Free energy (G) is a measure of useful energy in a system.
ΔG is the change in free energy and reflects the chemical potential of a system.
ΔG is negative for exergonic reactions (energy released) and positive for endergonic reactions (energy absorbed).
ΔG of zero indicates that the system is at equilibrium.
ΔGo' is the standard free energy change at pH 7.0.

Standard Free Energy Change

Endergonic reactions require energy (ΔGo' is positive).
Exergonic reactions release energy (ΔGo' is negative).
Isoergonic reactions are at equilibrium (ΔGo' is zero).

Substrate Level Phosphorylation

Produces ATP through direct transfer of a phosphate group from a substrate to ADP.
Only produces 1 ATP molecule at a time.
Does not involve electron transport chain.

Importance of ATP

Intermediate position of ATP allows it to play a critical role in energy transfer.
ATP allows the coupling of thermodynamically unfavorable reactions to favorable ones.

Coupling Exergonic and Endergonic Reactions

Energy released from an exergonic reaction can be used to drive an endergonic reaction, by transferring energy via a high-energy compound like ATP.

Creatine Phosphate

Found in skeletal muscles.
Acts as an energy source.
Creatine kinase (CK) facilitates the reversible transfer of a phosphate group from creatine phosphate to ADP, producing ATP.

Importance of Pyrophosphate (PPi)

Pyrophosphate can be further hydrolyzed to release additional energy (-4.6 kJ/mol).
When AMP + PPi are completely hydrolyzed, the overall energy release is -12.3 kJ/mol.
The presence of PPi in reactions can make them irreversible.

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Description

Explore the intricate process of oxidative phosphorylation, highlighting the roles of NADH and FADH2 in ATP production. Delve into the chemiosmotic coupling theory and understand how the electron transport chain contributes to energy generation in mitochondria. This quiz will test your knowledge of these essential biochemical processes.