Biochem 12.2 Electron Transport Chain Overview

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Questions and Answers

What is the primary purpose of the malate-aspartate shuttle?

To transfer electrons from the mitochondria to the cytosol

To transport ATP from the mitochondria to the cytosol

To regenerate NAD+ from NADH in the cytosol (correct)

To oxidize FADH2 back to FAD

Which complex in the electron transport chain serves as the entry point for FADH2?

Complex IV

Complex I

Complex III

Complex II (correct)

What is the end product of the glycerol-3-phosphate shuttle?

FADH2 (correct)

Lactate

NAD+

Pyruvate

How does NADH generated in glycolysis interact with the electron transport chain?

It requires transport via shuttles to enter the mitochondria Signup and view all the answers

Which of the following statements accurately describes Complex II?

It is part of the citric acid cycle as succinate dehydrogenase Signup and view all the answers

What molecule is ultimately reduced to form FADH2 in the Complex II reaction?

Succinate Signup and view all the answers

What is a major outcome of the glycerol-3-phosphate shuttle?

Restoration of DHAP without proton translocation Signup and view all the answers

What role does ubiquinone play in the electron transport chain?

It accepts electrons from both Complex I and Complex II Signup and view all the answers

What is the primary role of the electron transport chain?

To facilitate oxidation-reduction reactions to produce ATP Signup and view all the answers

Which molecule acts as the final electron acceptor in the electron transport chain?

Molecular oxygen (O2) Signup and view all the answers

What is produced as a result of the oxidation of NADH in Complex I?

NAD+ and Ubiquinol (QH2) Signup and view all the answers

How do protons contribute to ATP production in the electron transport chain?

They create a proton gradient that drives ATP synthase Signup and view all the answers

Which of the following statements about Complex I is true?

It oxidizes NADH by dehydrogenation Signup and view all the answers

What characteristic of NADH contributes to its interaction with Complex I?

It is a hydrophilic molecule found in aqueous environments Signup and view all the answers

What effect does the proton gradient have on the pH of the mitochondrial matrix compared to the intermembrane space?

The matrix has a lower proton concentration and higher pH Signup and view all the answers

Which of the following processes occurs as electrons are transferred in the electron transport chain?

Creation of a proton gradient Signup and view all the answers

Which molecule is the final electron acceptor in the electron transport chain?

Oxygen gas (O2) Signup and view all the answers

What happens to cyt c under anaerobic conditions?

It remains reduced. Signup and view all the answers

What does the reduction of one oxygen molecule yield in terms of water production?

Two water molecules Signup and view all the answers

How many protons are pumped into the intermembrane space for each NADH molecule that enters the electron transport chain?

Two protons Signup and view all the answers

What is required for the full reduction of a single oxygen molecule at Complex IV?

Two NADH molecules or two FADH2 molecules Signup and view all the answers

What effect does the inhibition of the citric acid cycle have on metabolic intermediates?

Buildup of NADH and FADH2 Signup and view all the answers

Which process does not occur when oxygen is absent in cellular respiration?

Electron transport chain function Signup and view all the answers

What role do proteases such as caspase play in apoptosis?

They degrade specific proteins. Signup and view all the answers

What type of protein is cytochrome c in the context of this content?

A soluble protein found in the intermembrane space Signup and view all the answers

What is the primary function of Complex III in the electron transport chain?

To transfer electrons from ubiquinol to cytochrome c Signup and view all the answers

During the Q cycle, what happens to the original ubiquinol molecule (QH2)?

It becomes oxidized to ubiquinone (Q) Signup and view all the answers

What does the semiquinone radical signify in the Q cycle?

It indicates the presence of an unpaired electron Signup and view all the answers

What can result from the highly reactive semiquinone produced in Complex III?

Formation of reactive oxygen species like superoxide Signup and view all the answers

What specifically initiates the Q cycle?

The interaction of two coenzyme Q molecules Signup and view all the answers

What is a consequence of oxidative stress in cells?

Oxidation of cellular components that should remain reduced Signup and view all the answers

Why must oxygen gas cross into the hydrophobic portion of the inner mitochondrial membrane?

To interact with Complex IV Signup and view all the answers

Study Notes

Electron Transport Chain (ETC)

The ETC is a series of oxidation-reduction reactions in the inner mitochondrial membrane.
These reactions begin with the oxidation of NADH or FADH2, products of the citric acid cycle and other metabolic processes.
Electrons from NADH and FADH2 are passed through intermediates, with oxygen (O2) as the final electron acceptor.
Oxygen is converted to water in this process.

Complexes in the ETC

Three complexes (Complex I, III, and IV) use energy released to pump protons from the mitochondrial matrix to the intermembrane space.
This creates a proton gradient, with a lower proton concentration (higher pH) in the matrix and a higher concentration in the intermembrane space.

Complex I (NADH:ubiquinone oxidoreductase/NADH dehydrogenase)

Oxidizes NADH by removing a hydride ion.
Transfers the hydride ion to ubiquinone (coenzyme Q), converting it to ubiquinol (QH2).
Pumps four protons (H+) from the mitochondrial matrix to the intermembrane space.
The standard potential (E′°) for electron transfer from NADH to ubiquinone is +0.365 V.

Complex II (Succinate dehydrogenase)

Oxidizes succinate to fumarate, reducing FAD to FADH2.
FADH2 passes electrons to ubiquinone, converting it to ubiquinol (QH2).
This reaction does not directly contribute to the pH gradient.

Complex III (Ubiquinone:cytochrome c oxidoreductase)

Transfers electrons from ubiquinol (QH2) to cytochrome c (cyt c).
Pumps four protons.
Cytochrome c is a protein with a heme prosthetic group, in the oxidized (+3) state (cyt c ox) and the reduced (+2) state (cyt c red).

Complex IV (Cytochrome c oxidase)

Oxygen (O2) binds to Complex IV, and four cytochrome c (cyt c) molecules pass their electrons.
Each oxygen atom reacts with two protons, producing two water molecules.
Four protons are pumped during the process.

Malate-Aspartate Shuttle

Allows cytosolic NADH to generate mitochondrial NADH without using fermentation.
Converts oxaloacetate to malate in the cytosol, which then enters the mitochondria.
The resulting NADH in the matrix contributes to the ETC.

Glycerol-3-Phosphate Shuttle

Another method for transferring electrons from cytosolic NADH to the mitochondrial ETC.
Does not pump protons, resulting in less ATP production compared to the malate-aspartate shuttle.

Oxidative Stress

Oxygen's interaction in Complex III can produce reactive oxygen species (ROS).
ROS can damage cellular components and trigger apoptosis.
Superoxide dismutase and catalase help mitigate oxidative stress.

Oxygen Availability

ETC cannot function without oxygen.
In anaerobic conditions, reduced cytochrome c builds up, and the citric acid cycle is inhibited.

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Description

Test your knowledge on the Electron Transport Chain (ETC) and its key processes within cellular respiration. This quiz covers the oxidation of NADH and FADH2, the role of complexes, and the creation of the proton gradient. Dive into the specifics of complex I and its function in mitochondrial energy production.