Bioenergetics and Oxidative Phosphorylation

Bioenergetics and Oxidative Phosphorylation

• Bioenergetics is the transfer and utilization of energy in biological systems.
• Changes in free energy (ΔG) predict whether a reaction will occur. This depends only on the initial and final states and does not account for the pathway.
• ΔG = ΔH - TΔS, where ΔH is enthalpy, T is temperature, and ΔS is entropy.
• A negative ΔG indicates a favorable, spontaneous reaction
• A positive ΔG indicates an unfavorable, non-spontaneous reaction
• A ΔG of zero indicates the reactants are in equilibrium
• The ΔG of a reaction depends on the concentrations of reactants and products, and temperature: ΔG = ΔG° + RT ln ([B]/[A]).

ATP as an Energy Carrier

• ATP is a multi-subunit enzyme that synthesizes ATP.
• ATP is formed by coupling endergonic reactions to exergonic reactions (e.g., ATP hydrolysis).
• ATP is used to store and transport chemical energy within cells.
• ATP has three phosphate groups - one is released to form ADP (adenosine diphosphate) or two to from AMP (adenosine monophosphate).
• ATP is a high-energy phosphate compound, and ΔG° for hydrolysis is -7.3 kcal/mol.

Electron Transport Chain (ETC)

• The ETC is a series of protein complexes located in the inner mitochondrial membrane.
• Electrons are passed along the chain, releasing energy.
• This energy is used to pump protons (H+) from the matrix to the intermembrane space
• The ETC is essential for oxidative phosphorylation.
• Components include Complex I, II, III, IV, and V (ATP synthase)
• NADH and FADH₂ donate electrons to the ETC
• Electrons ultimately combine with Oxygen and protons to form water.
• The ETC accounts for the greatest portion of the body's use of oxygen.

Chemiosmotic Hypothesis

• Electron transport is coupled to the phosphorylation of ADP by the pumping of protons across the inner mitochondrial membrane.
• This creates an electrical and pH gradient, the energy is used to drive ATP synthesis.
• Pumping occurs at complexes I, III, and IV.

ATP Synthase

• A multi-subunit enzyme that synthesizes ATP using the energy stored in the proton gradient
• Protons flow from the intermembrane space back into the matrix through the Fo complex. This drives rotation that phosphorylates ADP to ATP.

Site-Specific Inhibitors

• Inhibitors block electron transfer, disrupting the ETC and ATP synthesis
• Examples include amytal, rotenone, antimycin A, CN-, CO, H2S, and NaN3.

Phosphorylation of ADP to ATP

• The transfer of electrons through ETC is energetically favorable
• NADH is a strong electron donor
• O₂ is a strong electron acceptor
• Compounds with high negative E° are strong reducing agents/electron donors

Coupling in Oxidative Phosphorylation

• Coupling in Oxidative Phosphorylation describes the connection between the electron transport chain (ETC) and ATP synthesis.
• Oligomycin is a proton channel inhibitor which prevents ATP synthesis by binding to Fo and blocking protons re-entering the matrix

Uncoupling Proteins (UCPs)

• UCPs allow protons to reenter the mitochondrial matrix without generating ATP.
• The energy released is dissipated as heat (nonshivering thermogenesis)
• UCP1, found in brown adipose tissue, generates heat as it allows protons to re-enter.

Synthetic Uncouplers

• Synthetic uncouplers like 2,4-dinitrophenol (DNP) readily diffuse across the inner mitochondrial membrane, uncoupling the ETC and ATP synthesis
• The energy released from the uncoupling process is dissipated as heat.
• Aspirin and other salicylates are also synthetic uncouplers.

Explore the concepts of bioenergetics and oxidative phosphorylation through this quiz. Understand how changes in free energy influence chemical reactions and the role of ATP as an energy carrier in biological systems. Test your knowledge on crucial equations and principles governing energy transfer.