Overview
biological oxidation concept
The process in which organic compounds (sugar, fat, and protein) are oxidized and decomposed within biological cells to generate CO2 and H2O, and release energy.
3 main questions
How do cells convert C in organic compounds into CO2 through chemical changes?
Metabolites such as sugars, lipids, and proteins are converted into compounds with carboxyl groups through a series of dehydrogenation, water addition, and other reactions under the catalysis of enzymes, and then CO2 is produced through decarboxylation reactions.
How do cells use O to oxidize H in organic molecules into H2O?
The H on the metabolites is taken off under the action of dehydrogenase, accepted by the corresponding hydrogen carriers (NAD, NADP, FAD, FMN, etc.), and then transferred to oxygen through a series of hydrogen transfer bodies or electron transfer bodies to generate H2O
How is the energy released when organic compounds are oxidized within cells harvested?
A large amount of energy released by the electron transport chain is converted into ATP through phosphorylation
Free Energy
Free energy G: refers to the part of energy that can be used to do useful work in a system, represented by the symbol G.
△G: Free energy change under any given conditions. △G<0 is a necessary condition for the reaction to proceed spontaneously. Enzymes can only catalyze reactions in which △G is a negative value.
△G◦′: It is the free energy change under standard conditions, that is, the starting concentration of the reactants is 1mol/L, the temperature is 25℃, and the △G when pH=7.0. Each chemical reaction has its specific standard free energy change (ie △G◦′), which is a fixed value
ΔG calculation
Reaction A→B: ΔG = ΔGº′ RT ln[B]/[A]
Reaction equilibrium constant K′
[Product]/[Substrate] when the reaction reaches equilibrium under standard conditions. K′ for a particular reaction is a constant
ΔGº ′= -2.303 RT lgK′= -5706 lgK′ (J/mol)
K′<1, ΔGº′ is positive, it is an endothermic reaction and cannot proceed spontaneously.
K′>1, ΔGº′ is negative, exergonic reaction can proceed spontaneously
Oxidation-reduction potential E
Indicates how easy it is for the reducing agent to lose electrons (how easy it is for the oxidizing agent to obtain electrons),
E0: standard redox potential
Under standard conditions, compare the potential difference obtained with the standard hydrogen electrode
E0′
E0 of biological redox couple measured at pH=7
The relationship between ΔG0′ and ΔE0′
High energy phosphate compounds
Phosphate compounds that can release more than 25kJ of energy per mole of phosphate group upon hydrolysis. High energy bonds are represented by ~
Classification
Phosphorus-oxygen bond type -O～P
①Acyl phosphate compounds: such as carbamoyl phosphate
② Enol phosphate compounds: such as phosphoenol pyruvate
③Pyrophosphate compounds: such as pyrophosphate, ATP (adenosine triphosphate)
Phosphorus-nitrogen bond type -N～P: such as creatine phosphate, which plays a role in storing energy in the body
ATP
The free energies released by hydrolysis and cleavage of the two phosphate groups (β, γ) in the ATP molecule are -32.2 KJ/mol and -30.5 KJ/mol respectively.
Function
It is a chemical coupling agent for energy-producing reactions and energy-demanding reactions in cells.
The currency of energy in living organisms, rather than the energy storage material
It is an intermediate carrier for intracellular phosphate group transfer.
Mitochondria and their oxidative system
structure of mitochondria
electron transport chain
basic concept
During the biological oxidation of respiratory substrates (metabolites) in the mitochondrial matrix, H on the substrate is transferred through a series of hydrogen carriers or electron carriers, and finally transferred to O2 to generate H2O. The entire system is called the electron transport chain because of its function Directly related to respiration, also known as the respiratory chain.
type
1. NADH oxidation respiratory chain (most)
NADH → Complex I → CoQ → Complex III → Cyt c → Complex IV → O2
2. FADH2 respiratory chain (a few, such as succinic acid, fatty acyl-CoA, a-glycerol phosphate, etc.)
Succinic acid →Complex II →CoQ →Complex III →Cyt c →Complex IV →O2
Oxidative phosphorylation
concept
During the electron transfer process in the respiratory chain, the free energy released when electrons are transferred from the oxidized substrate to oxygen (i.e., H is oxidized to form H2O) drives the phosphorylation of ADP to generate ATP.
basic mechanism
When the electrons from the intermediate metabolite NADH or FADH2 are transferred to oxygen to generate water through the electron transport chain, a large amount of energy is released. This part of the energy can drive ADP and Pi to synthesize ATP.
Oxidative-phosphorylation coupling
Phosphorus to oxygen ratio P/O
Concept: During the oxidative phosphorylation process, the number of moles of inorganic phosphorus (or ADP) consumed or the number of moles of ATP generated for every 1 mol of oxygen consumed
The P/O of the NADH respiratory chain is 2.5, and the P/O of the FADH respiratory chain is 1.5.
coupling mechanism
chemical osmosis theory
① In the respiratory chain, hydrogen-transmitting bodies and electron-transmitting bodies are alternately arranged on the inner membrane of intact mitochondria, allowing the oxidation-reduction reaction to proceed in a directed manner.
②The electron transport chain has the function of a proton pump, which can pump protons from the inside of the inner mitochondrial membrane to the outside of the inner membrane.
③The intact inner mitochondrial membrane is selectively permeable to ions and cannot allow the protons pumped to the outside of the inner membrane to freely return to the inner membrane. This results in a difference in proton concentration and potential across the membrane, which becomes the driving force for protons to return to the inside of the inner membrane (protons). dynamic potential).
④When the protons on the outside of the membrane are driven by the proton dynamic potential and pass through the special channel FO on the ATP complex enzyme embedded in the inner mitochondrial membrane, free energy is released to drive ADP and Pi to form ATP.
ATPase (proton pump ATP synthase, F1F0-ATPase, complex V)
The function of F1 is to catalyze the generation of ATP, and the function of F0 is to form a channel for protons.
oxidative phosphorylation regulation
breath control
Due to the regulatory effect of changes in the ADP/ATP ratio on oxidative phosphorylation, it is called respiratory control, and the key substance for regulation is ADP
When the ADP/ATP ratio increases, oxidative phosphorylation increases; when the ADP/ATP ratio decreases, oxidative phosphorylation slows down.
uncoupling and inhibition
uncoupling agent
Destroying the proton electrochemical gradient across the inner membrane established by the electron transfer process causes the energy stored in the electrochemical gradient to be released in the form of heat energy, and the generation of ATP is inhibited. Such as: dinitrophenol (DNP); uncoupling protein
respiratory chain inhibitors
Blocks the electron transport process of oxidative phosphorylation. Such as rotenone; pieterin A; amobarbital; antimycin A; dimercaprol; CO; CN-; N3-; H2S
ATP synthase inhibitor
It can prevent protons from flowing back from the F0 proton channel and inhibit ATP production.
Oxidative phosphorylation of extramitochondrial NADH
Alpha-glycerol phosphate shuttle
NADH oxidation respiratory chain pumps out 10 H: 10/4=2.5 (molecular ATP)
FADH2 oxidation respiratory chain pumps out 6 H: 6/4=1.5 (molecular ATP)
Ubiquinone and Cyt c are not included in the four complexes (courier role)
n, the amount of substance that transfers electrons (mol);
F, Faraday’s constant, 96.5 KJ/V.mol
Electrons always flow from a low potential (E0′ low) redox pair to a high potential (E0′ high) redox pair (i.e. reaction direction)
Temperature (unit K) T=Celsius 273
Gas constant R=8.314
[Key Points] Master some basic knowledge involved in material metabolism and energy metabolism, master the types and compositions of biological oxidative respiratory chains, and master oxidative phosphorylation and other ATP generation methods.
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