Biochem 12.3 Oxidative Phosphorylation Overview

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Questions and Answers

What effect do uncouplers like 2,4-DNP and FCCP have on ATP production in mitochondria?

They increase ATP production by enhancing proton flow through ATP synthase.

They generate ATP at an increased rate despite the presence of protons.

They allow protons to return to the matrix without generating ATP. (correct)

They completely inhibit the electron transport chain.

How do uncouplers affect oxygen consumption during cellular respiration?

Oxygen consumption continues or may increase despite reduced ATP synthesis. (correct)

Oxygen consumption decreases due to diminished electron transport chain activity.

Oxygen consumption remains constant regardless of proton flow.

Oxygen consumption stops completely when uncouplers are introduced.

What is the role of thermogenin (UCP1) in brown adipose tissue under cold conditions?

It prevents protons from entering the mitochondria.

It enhances ATP synthesis by increasing proton flow through ATP synthase.

It stimulates the electron transport chain to produce excess ATP.

It allows protons to flow into the matrix, generating heat instead of ATP. (correct)

What is the consequence of a smaller pH gradient in the presence of uncouplers?

Protons have a reduced ability to flow through ATP synthase. Signup and view all the answers

What is one main reason that warm-blooded organisms might induce uncoupling during respiration?

To convert energy into heat to maintain body temperature in cold environments. Signup and view all the answers

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

To create a proton concentration gradient across the mitochondrial membrane Signup and view all the answers

What does the proton motive force primarily depend on?

The concentration gradient of protons Signup and view all the answers

Which complex is responsible for coupling the flow of protons with ATP synthesis?

ATP synthase Signup and view all the answers

What is the approximate pH of the intermembrane space in a typical healthy mammalian cell?

7.4 Signup and view all the answers

Which statement about protons and the mitochondrial membrane is true?

Protons require a channel or carrier protein to cross the membrane Signup and view all the answers

How is ATP synthesis powered in oxidative phosphorylation?

By the oxidation of NADH and FADH2 Signup and view all the answers

Why is the term 'proton motive force' considered a misnomer?

Because it does not imply a direct force acting on protons Signup and view all the answers

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

To convert ADP and Pi into ATP Signup and view all the answers

What conformation of the aß complex binds ADP and inorganic phosphate?

Dimer 1 Signup and view all the answers

How many protons are required for one complete rotation of the y unit in ATP synthase?

3 protons Signup and view all the answers

What event occurs when Dimer 2 of the aß complex changes conformation?

It releases ATP. Signup and view all the answers

What process describes the transport of ATP out of the mitochondrial matrix?

Antiport system Signup and view all the answers

What additional proton is necessary for synthesizing cytosolic ATP?

A proton moving through the phosphate transporter Signup and view all the answers

Which of the following statements about ATP synthase is true?

It relies on the proton gradient created by the electron transport chain. Signup and view all the answers

What is the consequence of the uncoupling of ATP synthase from the electron transport chain?

Decreased proton gradient Signup and view all the answers

How many protons must move into the matrix for one ATP molecule to be synthesized in total?

4 protons Signup and view all the answers

What role does ATP synthase play in cellular respiration?

It synthesizes ATP by coupling proton transport to their electrochemical gradient. Signup and view all the answers

Which components make up the ATP synthase enzyme?

Fo and F1 domains Signup and view all the answers

What happens to the c subunits of the F_o domain during ATP synthesis?

They undergo rotation upon binding protons. Signup and view all the answers

How is the rotation of the y subunit related to ATP synthesis?

It induces conformational changes in the αβ complexes. Signup and view all the answers

What type of transport does ATP synthase primarily facilitate?

Passive transport of protons into the matrix. Signup and view all the answers

What distinguishes ATP synthase from other translocases like the Na+/K+ pump?

ATP synthase synthesizes ATP while others do not. Signup and view all the answers

What is the function of the b subunits in the F_o domain?

They act as a homodimeric arm interacting with the F1 domain. Signup and view all the answers

Which statement about the αβ complexes in the F₁ domain is correct?

They surround the y subunit and change conformations independently. Signup and view all the answers

Study Notes

Oxidative Phosphorylation Introduction

Electron transport chain creates a higher proton concentration outside the mitochondrial matrix, a lower pH outside of the matrix.
This difference in concentration and charge is a source of stored energy called the proton motive force.
Excess protons flow back into the matrix through ATP synthase.
ATP synthase couples the flow of protons to ATP synthesis, from ADP and inorganic phosphate.
This process is called oxidative phosphorylation because it is powered by the oxidation of NADH and FADH2.

The Proton Motive Force

Electron transport chain pumps protons from the mitochondrial matrix to the intermembrane space.
This creates a lower pH in the intermembrane space than the matrix.
In healthy mammalian cells, the intermembrane space pH is approximately 7.4 and the matrix pH is ~7.8.
Differences in proton concentration creates a voltage.
The charge and concentration difference create an electrochemical gradient called the proton motive force (pmf).
Protons/ions cannot readily cross a phospholipid bilayer.
Proteins, channels or carriers are needed for this transport into the matrix (passive transport)
Active transport of protons out of the matrix, followed by passive transport back in is facilitated by ETC and ATP synthase.

ATP Synthase Mechanism

ATP synthase is also known as Complex V of the electron transport chain, and is a translocase enzyme.
It couples the transport of H+ down its gradient with ATP synthesis by chemiosmosis.
Structure includes F0 and F1 domains.
F0 is a transmembrane complex where protons flow.
Each c subunit in F0 binds a proton.
The rotation of the c subunits results in the rotation of the internal y subunit.
This rotation changes the conformation of the three αβ dimer complexes in F1 ,which converts ADP to ATP.

ATP Yield per Glucose

On average, one NADH yields 2.5 ATP, as 10 protons are pumped per NADH in the electron transport chain.
One FADH2 yields 1.5 ATP, as 6 protons are pumped per FADH2 in the electron transport chain.
Glycolysis produces 2 ATP,and 2 NADH.
Pyruvate oxidation produces 2 NADH.
The citric acid cycle produces 2 GTP, 6 NADH, 2 FADH2.
In total, glucose generates ~32 ATP molecules

Uncoupling of ATP Synthase

ATP synthase is coupled to the electron transport chain.
Uncouplers (e.g., 2,4-dinitrophenol (2,4-DNP), FCCP), allow protons to cross the inner mitochondrial membrane directly, bypassing ATP synthase.
This results in a decrease in ATP synthesis, as the proton gradient is not used for ATP production.
Heat is generated instead, which helps maintain temperature in endothermic organisms (warm blooded animals) in cold conditions by activating enzymes called thermogenin.

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Description

Explore the fundamental concepts of oxidative phosphorylation, including the electron transport chain and the proton motive force. Understand how ATP synthase synthesizes ATP powered by the oxidation of NADH and FADH2, and the implications of pH differences in mitochondrial function.