Biochemistry Chapter: Cellular Respiration

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Questions and Answers

What facilitates the return of phosphate to the mitochondrion?

Phosphate carrier/translocase (correct)

Proton pump

ATP synthase

NADH transporter

What is the theoretical maximum ATP yield from one molecule of glucose?

26 or 28 ATP

34 or 36 ATP

20 or 22 ATP

30 or 32 ATP (correct)

How many protons are pumped as a result of the oxidation of one NADH molecule?

6 protons

8 protons

12 protons

10 protons (correct)

What drives the synthesis of approximately 2.5 ATP molecules per NADH oxidized?

Electron transport from NADH to O2 Signup and view all the answers

How many ATP are synthesized from one FADH2 molecule?

2 ATP Signup and view all the answers

What is the energy change ($ riangle G'$) for the reaction involving NADH and O2?

$-218 kJ mol^{-1}$ Signup and view all the answers

What is the role of 3-phosphoglycerol dehydrogenase in the cytosol?

Converts dihydroxyacetone phosphate to glycerol-3-phosphate. Signup and view all the answers

During glycolysis, how many NADH are produced per glucose molecule?

2 NADH Signup and view all the answers

What role does the proton gradient play in the mitochondrial function?

It drives ATP production Signup and view all the answers

Which enzyme is responsible for the phosphorylation of fructose in muscle tissue?

Hexokinase Signup and view all the answers

In the liver, how is fructose-1-phosphate split?

By fructose-1-phosphate aldolase Signup and view all the answers

What is one effect of reactive oxygen species (ROS) on cellular components?

Causing DNA damage Signup and view all the answers

What happens to glycerol-3-phosphate in the mitochondria?

It is oxidized back to DHAP. Signup and view all the answers

During the oxidation of glycerol-3-phosphate to DHAP, which electron carrier is produced?

FADH2 Signup and view all the answers

Which reaction involves ferrous iron and hydrogen peroxide leading to the formation of hydroxyl radicals?

Fenton reaction Signup and view all the answers

Which category of antioxidants functions by binding free radicals?

Proteins Signup and view all the answers

Which of the following tissues primarily carries out fructose metabolism?

Liver and muscle tissues. Signup and view all the answers

Which of the following is NOT classified as an antioxidant?

Hydrogen peroxide Signup and view all the answers

What is the significance of the glycerol phosphate shuttle?

It is crucial for rapid ATP production in tissues during exercise. Signup and view all the answers

What product results from the superoxide dismutase reaction?

Oxygen and water Signup and view all the answers

What reduces NAD+ to NADH during the conversion of DHAP to glycerol-3-phosphate?

3-phosphoglycerol dehydrogenase Signup and view all the answers

Which antioxidants are well-known for scavenging free radicals?

Vitamin C and Vitamin E Signup and view all the answers

How does glutathione function in the antioxidant defense?

It can be regenerated from its oxidized form Signup and view all the answers

What role do buffering ions like iron and copper play in oxidative stress?

They contribute to antioxidant defense Signup and view all the answers

What allows Complex II to maintain some ATP production when Complex I is inhibited?

It receives electrons from FADH₂ derived from succinate. Signup and view all the answers

What is the primary function of the F0 portion of ATP synthase?

It undergoes proton translocation. Signup and view all the answers

What happens to the c subunit ring when protons bind to aspartic acid residues?

It shifts 30-40 degrees clockwise. Signup and view all the answers

What occurs during the Open State (O) in ATP synthesis?

ADP and inorganic phosphate (Pi) enter the complex. Signup and view all the answers

How does the rotation of the c subunit ring contribute to ATP synthesis?

It mechanically influences the F1 component to synthesize ATP. Signup and view all the answers

What occurs during the transition from the L state to the T state in ATP synthesis?

ATP is formed from ADP and Pi Signup and view all the answers

Which enzyme is responsible for converting oxaloacetate to malate in the cytosol during the malate-aspartate shuttle?

Malate dehydrogenase Signup and view all the answers

Which subunits make up the F1 portion of ATP synthase?

Alpha (α) and beta (β) subunits arranged in a hexagonal array. Signup and view all the answers

What is the main function of the malate-aspartate shuttle?

Transport NADH into the mitochondria Signup and view all the answers

What is the significance of Complex II's ability to function independently of Complex I?

It allows for minimal ATP production even during complex inhibition. Signup and view all the answers

Which component of ATP synthase is primarily involved in proton binding?

C subunits of F0. Signup and view all the answers

How many ATP molecules are synthesized during each full rotation of the F1 component?

Three ATP Signup and view all the answers

What role does aspartate aminotransferase play in the malate-aspartate shuttle?

Converts oxaloacetate to aspartate Signup and view all the answers

Which antiporter is involved in transporting malate into the mitochondrial matrix?

Malate-α-ketoglutarate antiporter Signup and view all the answers

What is the primary tissue where the malate-aspartate shuttle operates?

Liver, heart, and kidney Signup and view all the answers

In the glycerol phosphate shuttle, what is the primary role of this mechanism?

Transfer reducing equivalents from the cytosol to mitochondria Signup and view all the answers

What is the primary function of catalase in the body?

To break down hydrogen peroxide into water and oxygen Signup and view all the answers

What is the primary role of uncoupling protein 1 (UCP-1) in nonshivering thermogenesis?

To uncouple the electron transport chain from ATP synthesis Signup and view all the answers

Which factor initiates the activation of UCP-1 in response to cold temperatures?

Norepinephrine Signup and view all the answers

What type of animals predominantly utilize nonshivering thermogenesis to maintain body temperature?

Endothermic animals Signup and view all the answers

What is the consequence of UCP-1 allowing protons to flow back into the mitochondrial matrix?

Dissipation of the proton gradient and heat production Signup and view all the answers

Which physiological context is particularly dependent on nonshivering thermogenesis?

Maintaining elevated body temperature in cold environments Signup and view all the answers

What is the primary reaction outcome of peroxidase activity?

Reduction of hydrogen peroxide by various substrates Signup and view all the answers

In nonshivering thermogenesis, the energy from nutrient oxidation is primarily released as:

Heat instead of ATP Signup and view all the answers

Study Notes

Electron Transport Chain Overview

The Electron Transport Chain (ETC) is vital for cellular respiration, located in the inner mitochondrial membrane.
It drives ATP production through oxidative phosphorylation.
The process starts with electrons from reduced substrates (NADH and FADH2), generated in glycolysis and the citric acid cycle.
These electrons are transferred through protein complexes (I, II, III, IV) and electron carriers, ultimately reducing oxygen to form water.
Energy released during electron flow pumps protons (H+) from the mitochondrial matrix to the intermembrane space, creating an electrochemical gradient.
This gradient provides the energy for ATP synthase to convert ADP and inorganic phosphate (Pi) to ATP.

Oxidative Fuel Production

The ETC is part of a larger process, including glycolysis and the citric acid cycle.
These pathways supply the electron carriers (NADH and FADH2) for the ETC.
NADH produces approximately 2.5 ATP molecules.
FADH2 produces approximately 1.5 ATP molecules.
Proton pumping coupled with electron flow establishes the essential proton gradient for ATP synthesis.

Mechanism of Proton Pumping

The ETC involves four main complexes.
Complex I accepts electrons from NADH, pumping 4 H+ ions into the intermembrane space.
Complex II accepts electrons from FADH2 but does not pump protons.
Complex III transfers electrons via the Q cycle, pumping 4 H+ across the membrane.
Complex IV receives electrons from cytochrome c, reducing O2 to H2O and pumping 2 H+.
The total protons pumped contribute to the proton-motive force that drives ATP synthesis.

Role of ATP Synthase

ATP synthase utilizes the electrochemical potential from the proton gradient.
As protons flow back into the mitochondrial matrix through ATP synthase, energy is released, converting ADP and inorganic phosphate (Pi) into ATP.
This process is essential for cellular energy production.

Summary of Electron Transport Chain Process

Electrons from NADH and FADH2 are transferred through the ETC.
The transfer process pumps protons into the intermembrane space, creating a gradient.
Oxygen acts as the final electron acceptor, forming water.
The proton gradient drives ATP synthesis via ATP synthase.

Oxidative Phosphorylation

Oxidative phosphorylation is a crucial metabolic process occurring in the mitochondria.
It produces ATP through the electron transport chain (ETC) and chemiosmosis.
The process uses energy from electron transfer from electron donors, such as NADH and FADH2, to oxygen (final electron acceptor).
The overall reaction is NADH + 1/2O2 + H+ → NAD+ + H2O.
Energy release from NADH-to-O2 transfer drives ATP synthesis.

Role of Electron Carriers

Electron carriers (NADH and FADH2) play a critical role in oxidative phosphorylation.
NADH produces approximately 2.5 ATP.
FADH2 produces approximately 1.5 ATP.
These carriers donate electrons to the ETC, passing them through protein complexes in the inner mitochondrial membrane.

Complex I: NADH Dehydrogenase

Complex I, also known as NADH dehydrogenase, plays a key role in the electron transport chain (ETC).
NADH is oxidized to NAD+ releasing two electrons (2e-).
Electrons are transferred through Flavin mononucleotide (FMN) and Iron-sulfur clusters.
Four protons (4H+) are pumped into the intermembrane space per two electrons transferred.
Coenzyme Q (CoQ) receives transferred electrons and is reduced to QH2 (ubiquinol).

Complex II: Succinate Dehydrogenase

Complex II, also known as succinate dehydrogenase, is part of the electron transport chain (ETC).
It catalyzes the conversion of succinate to fumarate in the citric acid cycle.
FAD is reduced to FADH2, releasing two electrons (2e-).
Electrons are transferred through Fe-S clusters to CoQ, which reduces to QH2.
Complex II does not pump protons (H+) across the inner mitochondrial membrane.

Complex III: Q-Cytochrome C Oxidoreductase

Complex III, also known as Q-cytochrome c oxidoreductase, is involved in the electron transport chain (ETC).
QH2 binds to heme bL, then heme bH, where it is oxidized to Q, releasing 2 protons (2H+) and two electrons (2e-).
Electrons are transferred through iron-sulfur (Fe-S) clusters to cytochrome c, which then carries electrons to complex IV.
Complex III pumps 4 protons into the intermembrane space during the Q cycle.

Complex IV: Cytochrome C Oxidase

Complex IV (cytochrome c oxidase) is the final complex in the electron transport chain (ETC).
It receives electrons from cytochrome c, requiring four cytochrome c molecules to transfer a total of 4 electrons.
Electrons bind with copper subunits.
Four protons (4H+) and O2 are used to reduce oxygen to form two water molecules (2H2O).
Complex IV pumps two protons (2H+) into the intermembrane space per two electrons it transfers.

Summary of Proton Pumping

Complex I pumps 4 protons.
Complex II does not pump protons.
Complex III pumps 4 protons.
Complex IV pumps 2 protons.
The proton-motive force generated by these complexes drives ATP synthesis by ATP synthase.

ATP Synthase Mechanism

ATP synthase is a crucial enzyme for ATP production.
It consists of F0 and F1 portions.
The F0 portion is embedded in the inner mitochondrial membrane and is responsible for proton translocation.
The F1 portion protrudes into the mitochondrial matrix and is the site of ATP synthesis.
Protons flow back into the matrix through the F0 portion, driving the rotation of the c ring and the F1 portion, which catalyzes ATP synthesis from ADP and inorganic phosphate (Pi).

Shuttle Mechanisms

Malate-Aspartate Shuttle: Electrons from cytosolic NADH are transferred to the mitochondrial matrix via malate and aspartate.
Glycerol-3-Phosphate Shuttle: Transfers electrons from cytosolic NADH to FAD in the mitochondrial membrane, generating FADH2.

Mitochondrial Dysfunction: MERRF

Myoclonic Epilepsy with Ragged Red Fibers (MERRF) is a mitochondrial disorder.
It is maternally inherited and results in disruptions in the synthesis of proteins involved in oxidative phosphorylation.
Clinical features may include; myoclonic seizures, hearing loss, lactic acidosis, exercise intolerance, and poor night vision.
The results are due to accumulations of inactive mitochondria, leading to impaired ATP production.

ATP-ADP Translocation

The ATP-ADP translocator facilitates the exchange of ATP and ADP across the inner mitochondrial membrane.
ATP, in a net charge of -4, is exported from the matrix.
ADP, with a net charge of -3, is imported into the matrix.
This process involves Adenine nucleotide translocase as a carrier.
Proton gradient drives the transport.

Role of Uncoupling Proteins

Uncoupling protein 1 (UCP-1), primarily located in brown adipose tissue, allows protons (H+) to flow back into the mitochondrial matrix without passing through ATP synthase.
The process utilizes these protons for heat production instead of ATP synthesis.

Reduction Potentials

Reduction potential measures the tendency of a chemical species to acquire electrons.
A higher reduction potential indicates a greater tendency for reduction.
Reduction potentials are used to predict which species will act as electron donors and acceptors in chemical reactions.

Theoretical ATP Yield

Electron transfer from NADH generates approximately 2.5 ATPs.
Electron transfer from FADH2 generates approximately 1.5 ATPs.
Glycolysis, pyruvate oxidation, and the citric acid cycle contribute to the overall ATP yield.
The theoretical maximum ATP yield from glucose oxidation is 30-32 ATPs

Reactive Oxygen Species (ROS) Formation

ROS are formed through homolytic cleavage, resulting in unpaired electrons.
Key reactions for ROS formation include the Fenton and Haber-Weiss reactions.
ROS can damage DNA, lipids, proteins, and enzymes, leading to various cellular effects.

Antioxidants

Antioxidants neutralize the harmful effects of ROS.
Enzymes such as superoxide dismutase, catalase, and peroxidase contribute to this process.
Other antioxidants include vitamins C and E, buffering ions (like Fe and Cu), and specific proteins.

Nonshivering Thermogenesis

Nonshivering thermogenesis is a metabolic process in warm-blooded animals.
It generates heat by using energy from nutrient oxidation to release heat instead of converting to ATP.
Uncoupling protein 1 (UCP-1) plays a crucial role in the process, found primarily in brown adipose tissue.
Activation typically in response to cold environments.

Fructose Metabolism

Fructose metabolism is primarily in the liver and muscle tissue.
In muscles, fructose is phosphorylated into fructose-6-phosphate and enters glycolysis.
In the liver, fructose is phosphorylated to fructose-1-phosphate.
Fructose-1-phosphate is spilt into dihydroxyacetone phosphate and glyceraldehyde.
Glyceraldehyde and dihydroxyacetone phosphate can enter glycolysis.

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Description

Test your knowledge on cellular respiration, ATP synthesis, and the biochemistry of mitochondria. This quiz covers key concepts including the roles of NADH, FADH2, and the proton gradient. Explore how energy is produced at the cellular level!