Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Biochemistry → Metabolism and Bioenergetics ↓


Electron transport chain


In biochemistry, understanding how cells obtain energy from nutrients is important for understanding larger concepts in metabolism and bioenergetics. A central component of this energy conversion is the electron transport chain (ETC), a series of complexes located in the inner mitochondrial membrane.

The ETC is the third stage of cellular respiration after glycolysis and the Krebs cycle. At its core, the ETC is about transferring electrons through a series of protein complexes. This transfer creates a proton gradient that ultimately leads to the production of ATP, the cell's primary energy currency.

Basics of the electron transport chain

The electron transport chain consists of four main complexes (numbered I to IV) and two mobile carriers: ubiquinone (coenzyme Q) and cytochrome c. Let's look at each component:

Complex I: NADH-CoQ reductase

Complex I, or NADH-CoQ reductase, is the first step in the chain. Here, NADH, generated in glycolysis and the Krebs cycle, donates electrons. The simplified reaction is:

NADH + H + + CoQ → NAD + + CoQH 2

During this transfer, four protons (H +) are pumped from the mitochondrial matrix into the intermembrane space.

Complex I.Whyqh2

Complex II: succinate-CoQ reductase

Complex II, or succinate dehydrogenase, accepts electrons from another reduced molecule, FADH2, from the Krebs cycle. This process does not pump protons, which distinguishes it from Complex I. The reaction is:

FADH2 + CoQ → FAD + CoQH2

The resulting CoQH2 transfers electrons to Complex III, continuing the chain.

Complex III: CoQH2-cytochrome c reductase

Complex III accepts electrons from CoQH2 and facilitates transfer to cytochrome c, a mobile carrier. The main reaction in this complex is:

CoQH 2 + 2 cytochrome c ox → CoQ + 2 cytochrome c red

Again, in this step four protons are pumped into the intermembrane space.

Complex IIIC

Complex IV: cytochrome c oxidase

Complex IV, or cytochrome c oxidase, facilitates the final step. Here, electrons from cytochrome c are transferred to oxygen, which is the final electron acceptor. The reaction is as follows:

4 cytochrome c red + O 2 + 8 H + → 4 cytochrome c ox + 2 H 2 O + 4 H +

This complex pumps two protons into the intermembrane space.

ATP synthesis via the proton gradient

The role of the ETC is to create a proton gradient across the inner mitochondrial membrane. The potential energy in this gradient drives the synthesis of ATP by ATP synthase, a molecular motor. This process is known as chemiosmosis.

ATP synthase is embedded in the membrane and allows protons to flow back into the matrix. This flow converts ADP and inorganic phosphate (Pi) into ATP. The main reaction is:

ADP + Pi + Energy → ATP + H 2 O

ATP Synthase

Regulation and efficiency

The entire ETC operates with remarkable efficiency, extracting approximately 34 ATP molecules from each metabolized glucose molecule, depending on shuttle systems involved in the transfer of electrons from glycolytic NADH.

The regulation of the ETC is tightly controlled and responds to the energy demand of the cell. High levels of ADP stimulate the ETC, while high levels of ATP inhibit key enzymes, ensuring balance.

Pathophysiology

Dysfunction of the ETC can have serious consequences. Defects in any of the components can lead to diseases called mitochondrial disorders. These are associated with a decrease in ATP production, leading to muscle weakness and neurological deficits.

Conclusion

The electron transport chain plays a vital role in energy metabolism. It transfers electrons efficiently, creating a proton gradient that is used to generate ATP via chemiosmosis. Understanding the ETC is not only fundamental to biochemistry, but is also important in understanding metabolic diseases.

Through this overview, we have explored the complex nature of the ETC and its central role in cellular energy metabolism. Its functionality, regulation, and potential dysfunction highlight its importance in both health and disease.


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Electron transport chain

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