Bioenergetics and Oxidative Phosphorylation Overview

Bioenergetics

The study of energy transfer and utilization in biological systems, focusing on the changes in free energy during chemical reactions.

Free Energy (G)

A thermodynamic quantity that indicates the amount of energy available to do work in a system, determining the spontaneity of a reaction.

Change in Free Energy (∆G)

The difference in free energy between the products and reactants of a reaction, indicating whether the reaction can occur spontaneously.

Standard Free Energy Change (∆Go)

The change in free energy under standard conditions, typically at a concentration of 1 mol/L for all reactants and products.

Exergonic Reaction

A reaction that releases energy, characterized by a negative change in free energy (∆G < 0), indicating that it occurs spontaneously.

Endergonic Reaction

A reaction that requires an input of energy to proceed, characterized by a positive change in free energy (∆G > 0), indicating it does not occur spontaneously.

Enthalpy (∆H)

A measure of the total heat content of a system, which can influence the spontaneity of a reaction when combined with entropy.

Entropy (∆S)

A measure of the disorder or randomness in a system, which affects the spontaneity of a reaction but does not predict it alone.

Equilibrium

A state in a chemical reaction where the rates of the forward and reverse reactions are equal, resulting in no net change in the concentrations of reactants and products.

Thermodynamics

The branch of physics that deals with the relationships between heat, work, and energy, providing principles that govern bioenergetics.

Gas Constant (R)

A constant used in thermodynamic equations, equal to 1.987 cal/(mol·K), which relates temperature and energy.

Natural Logarithm (ln)

A mathematical function that is the inverse of the exponential function, often used in equations involving rates and concentrations.

Equilibrium Constant

A numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium, used to calculate ∆Go.

Concentration Ratio

The ratio of the concentration of products to reactants, which influences the direction and spontaneity of a reaction.

∆G

The change in free energy of a system, indicating the spontaneity of a reaction; negative values suggest a favorable process.

∆Go

The standard change in free energy under standard conditions, used to predict reaction direction only under those specific conditions.

Keq

The equilibrium constant representing the ratio of concentrations of products to reactants at equilibrium.

Additivity of ∆Go

The principle that the standard free energy changes of consecutive reactions can be summed to determine the overall free energy change of a pathway.

Coupling of Reactions

The process of linking a favorable reaction with an unfavorable one to drive the overall reaction forward.

ATP

A high-energy molecule that serves as an energy carrier in cells, facilitating various biochemical reactions.

Activation Energy

The minimum energy required to initiate a chemical reaction, often lowered by enzymes.

Concentration Gradient

A difference in the concentration of a substance across a space, which can drive the movement of substances.

Hydrolysis of ATP

The chemical reaction in which ATP is broken down into ADP and inorganic phosphate, releasing energy.

Spontaneous Process

A process that occurs without the need for external energy input, typically associated with a negative ∆G.

Physiologic Conditions

The conditions within a living organism, which can affect the direction and rate of biochemical reactions.

Chemical Equilibrium

The condition in which the concentrations of reactants and products remain constant over time.

R and T in ∆Go Equation

R is the universal gas constant and T is the temperature in Kelvin, both of which are used in the equation relating ∆Go to Keq.

Energy coupling

The process where energy from an exergonic reaction is used to drive an endergonic reaction, often involving a common intermediate.

Common intermediate

A product of one reaction that serves as a substrate for a subsequent reaction, facilitating the coupling of energy-requiring and energy-yielding processes.

ATP (Adenosine Triphosphate)

A high-energy molecule that serves as the primary energy carrier in cells, consisting of adenosine and three phosphate groups.

ADP (Adenosine Diphosphate)

A molecule formed when one phosphate group is removed from ATP, resulting in a lower energy state.

AMP (Adenosine Monophosphate)

A molecule produced when two phosphate groups are removed from ATP, representing an even lower energy state.

Oxidative phosphorylation

The metabolic process in which ATP is formed as a result of the transfer of electrons through the electron transport chain, coupled with the phosphorylation of ADP.

Electron transport chain

A series of protein complexes located in the inner mitochondrial membrane that transfer electrons derived from energy-rich molecules to oxygen.

NAD+ (Nicotinamide Adenine Dinucleotide)

A coenzyme that acts as an electron carrier in metabolic reactions, becoming reduced to NADH during the process.

FAD (Flavin Adenine Dinucleotide)

A coenzyme similar to NAD+, which accepts electrons and is reduced to FADH2 during metabolic reactions.

Cristae

The folds of the inner mitochondrial membrane that increase its surface area, enhancing the capacity for ATP production through oxidative phosphorylation.

High-energy phosphate compound

A term used to describe molecules like ATP that release a significant amount of energy upon hydrolysis of their phosphate bonds.

Metabolism

The set of life-sustaining chemical reactions in organisms that convert food into energy and building blocks for growth.

Phosphate group transfer

A biochemical process where a phosphate group is transferred from one molecule to another, often involving ATP as the donor.

Coenzymes

Organic molecules that assist enzymes in catalyzing reactions, often acting as carriers for electrons or functional groups.

Free energy

The energy in a system that can be used to do work, particularly in the context of chemical reactions.

Matrix

The gel-like solution in the interior of mitochondria, containing enzymes for oxidation and the TCA cycle, as well as mitochondrial DNA and RNA.

NAD+

An oxidized coenzyme that acts as a hydrogen acceptor in metabolic reactions, essential for energy production.

FMN

A coenzyme derived from riboflavin that participates in redox reactions, particularly in the electron transport chain.

Coenzyme Q (CoQ)

A mobile electron carrier in the electron transport chain that transfers electrons between complexes.

Complex I

A protein complex in the inner mitochondrial membrane that catalyzes the transfer of electrons from NADH to CoQ.

Complex II

A protein complex that catalyzes the oxidation of succinate to fumarate, contributing to the electron transport chain.

Complex III

A protein complex that transfers electrons from reduced CoQ to cytochrome c in the electron transport chain.

Complex IV

A protein complex that facilitates the transfer of electrons from cytochrome c to oxygen, forming water.

Complex V (ATP Synthase)

A protein complex that synthesizes ATP from ADP and inorganic phosphate, utilizing the proton gradient created by the electron transport chain.

TCA Cycle

A series of enzymatic reactions in the mitochondrial matrix that generates energy through the oxidation of acetyl-CoA.

β-Oxidation

The metabolic process by which fatty acids are broken down in the mitochondrial matrix to produce acetyl-CoA.

Cytochrome c

A small heme protein that transports electrons between Complex III and Complex IV in the electron transport chain.

Hydride Ion

A negatively charged ion consisting of one proton and two electrons, involved in the reduction of NAD+ to NADH.

Iron-Sulfur Centers

Metal clusters found in certain proteins that play a crucial role in electron transfer within the electron transport chain.

Mitochondrial Ribosomes

Ribosomes located in the mitochondrial matrix that are involved in synthesizing mitochondrial proteins.

Mitochondrial DNA (mtDNA)

The genetic material found in mitochondria, distinct from nuclear DNA, responsible for encoding some mitochondrial proteins.

Coenzyme Q (Ubiquinone)

A mobile carrier in the electron transport chain that accepts hydrogen atoms from various dehydrogenases and transfers electrons to Complex III.

Cytochromes

Proteins that contain heme groups and function as electron carriers, reversibly converting iron between ferric and ferrous states during electron transfer.

Cytochrome a + a3

The complex that acts as cytochrome oxidase, directly interacting with oxygen to reduce it to water, containing copper atoms essential for this reaction.

Site-specific inhibitors

Compounds that block electron transport by binding to specific components of the electron transport chain, preventing the oxidation/reduction reactions.

Reactive Oxygen Species (ROS)

Highly reactive molecules formed from incomplete reduction of oxygen, which can damage cellular components like DNA and proteins.

Redox pairs

Pairs of compounds where one is oxidized (loses electrons) and the other is reduced (gains electrons), such as NADH and NAD+.

NADH

A reduced form of nicotinamide adenine dinucleotide that serves as an electron donor in the electron transport chain.

FMN (Flavin mononucleotide)

A cofactor that accepts electrons from NADH and transfers them further along the electron transport chain.

Standard Reduction Potential (Eo)

A quantitative measure of the tendency of a redox pair to gain or lose electrons, expressed in volts.

Redox Pair

A pair of chemical species that undergo oxidation and reduction reactions, where one species donates electrons and the other accepts them.

Chemiosmotic Hypothesis

A theory that explains how the energy from electron transport is used to pump protons across a membrane, creating a gradient that drives ATP synthesis.

Proton Gradient

A difference in proton concentration across a membrane that generates potential energy used for ATP production.

ATP Synthesis

The process of producing adenosine triphosphate from adenosine diphosphate and inorganic phosphate, driven by energy from the proton gradient.

P:O Ratio

The ratio of ATP produced per atom of oxygen reduced in the electron transport chain, indicating the efficiency of oxidative phosphorylation.

Faraday Constant (F)

A constant representing the charge of one mole of electrons, used in calculations involving electrochemical reactions.

Oxidizing Agent

A substance that accepts electrons in a redox reaction, thereby causing another substance to be oxidized.

Reducing Agent

A substance that donates electrons in a redox reaction, thereby causing another substance to be reduced.

Complex I, III, IV

Specific protein complexes in the electron transport chain that facilitate the transfer of electrons and the pumping of protons.

Mitochondrial Matrix

The innermost compartment of the mitochondrion, where the Krebs cycle occurs and where NADH is generated.

Intermembrane Space

The space between the inner and outer mitochondrial membranes, where protons are pumped to create a gradient.

Oxygen as Electron Acceptor

Molecular oxygen acts as the final electron acceptor in the electron transport chain, forming water.

ADP + Pi

The substrates for ATP synthesis, where inorganic phosphate is added to adenosine diphosphate to form ATP.

ATP synthase

An enzyme complex that synthesizes ATP using the energy derived from a proton gradient across the inner mitochondrial membrane.

Uncoupling proteins (UCPs)

Proteins that allow protons to re-enter the mitochondrial matrix without generating ATP, releasing energy as heat instead.

Oligomycin

A drug that inhibits ATP synthesis by blocking the proton channel of ATP synthase, preventing protons from re-entering the mitochondrial matrix.

Respiratory control

The phenomenon where the rate of electron transport and ATP synthesis are tightly coupled, such that inhibition of one process affects the other.

Synthetic uncouplers

Compounds that increase the permeability of the inner mitochondrial membrane to protons, leading to heat production instead of ATP synthesis.

2,4-Dinitrophenol (DNP)

A synthetic uncoupler that disrupts the proton gradient, allowing protons to diffuse back into the matrix without generating ATP.

Nonshivering thermogenesis

The process of heat production in organisms, primarily through the action of uncoupling proteins in brown adipose tissue.

Brown adipose tissue

A type of fat tissue that is specialized for heat production through nonshivering thermogenesis, rich in uncoupling proteins.

ATP-ADP Transport

The process by which ADP is imported into mitochondria and ATP is exported to the cytosol, facilitated by specialized carriers.

Malate-Aspartate Shuttle

A mechanism that transfers reducing equivalents from cytosolic NADH into the mitochondrial matrix, producing NADH and yielding three ATPs.

Glycerol 3-Phosphate Shuttle

A pathway that transfers electrons from cytosolic NADH to dihydroxyacetone phosphate, resulting in FADH2 and the production of two ATPs.

Apoptosis

The process of programmed cell death that can be initiated by mitochondrial signals, leading to cellular changes and death.

Caspases

A family of proteolytic enzymes activated during apoptosis that cleave specific proteins to execute cell death.

Mitochondrial Myopathy

A group of disorders caused by defects in mitochondrial function, often resulting in muscle weakness and pain.

Leber Hereditary Optic Neuropathy

A genetic condition caused by mutations in mtDNA leading to vision loss due to neuroretinal degeneration.

Reducing Equivalents

Electrons transferred during metabolic reactions, often carried by NADH and FADH2, crucial for ATP production.

Phosphate Carrier

A transport protein responsible for moving inorganic phosphate (Pi) into mitochondria for ATP synthesis.

Gibbs Free Energy (∆G)

A thermodynamic quantity that indicates the spontaneity of a reaction; negative values suggest spontaneity, positive values indicate non-spontaneity, and zero indicates equilibrium.

Adenosine Triphosphate (ATP)

A high-energy molecule that serves as the primary energy currency of the cell, providing energy for various biochemical processes.

Electron Transport Chain (ETC)

A series of protein complexes located in the inner mitochondrial membrane that transfer electrons from donors like NADH to oxygen, coupled with proton transport.