Cellular Respiration & Chemiosmotic Theory

Energy Flow in Cellular Respiration Notes

• Carbohydrates, lipids, and amino acids serve as primary fuels.
• Electrons are transferred from the reduced fuels to NADH or FADH2.
• Oxidative phosphorylation uses the energy from NADH and FADH2 to synthesize ATP.

Chemiosmotic Theory Notes

• ADP + Pi → ATP is thermodynamically unfavorable.
• ATP phosphorylation is achieved using the flow of protons down the electrochemical gradient.
• Energy from electron transport helps to transport protons against the electrochemical gradient.

Chemiosmotic Energy Coupling Notes

• A proton gradient is required for ATP synthesis, established using a membrane impermeable to ions.
• Membranes for ATP synthesis: the plasma membrane in bacteria, the inner membrane in mitochondria, and the thylakoid membrane in chloroplasts.
• Proteins within the membrane couple the "downhill" flow of electrons to the "uphill" flow of protons.
• A protein in the membrane will couple the "downhill" flow of protons to the phosphorylation of ADP.

Mitochondria Membranes and Compartments

• Outer membrane: Porous, allowing metabolite passage.
• Intermembrane space: Environment is similar to the cytosol, higher proton concentration (lower pH).
• Inner membrane: Impermeable to protons; contains the electron transport chain complexes.
• Cristae are convolutions of the inner membrane that increase surface area.
• Matrix: Where the citric acid cycle and lipid/amino acid metabolism occur, lower proton concentration (higher pH).

Electron Transport Chain

• The electron transport chain creates an electrochemical potential to ultimately generate ATP.
• Redox centers include: flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD), cytochromes (a, b, or c), and iron-sulfur clusters.

Electron Transfer and Reduction Potential

• Electron transfer occurs from NADH/FADH2 to oxygen.
• ΔG = -n F Δεo, where ΔG is Gibbs free energy, n is the number of moles of electrons transferred, F is Faraday's constant, and Δεo is the change in standard reduction potential.
• NADH + H+ + 1/2 O2 → NAD+ + H2O, with ΔG approximately -220 kJ/mol.

Cofactors in the ETC

• Includes FAD/FMN, NADH, Coenzyme, and Iron-sulfur clusters.

NADH's Role in Electron Transfer

• The TCA cycle and fatty acid β-oxidation supply electrons for NAD+ reduction.
• NADH can only take up or release 2 electrons one at a time.

FMN and FAD as Electron Funnels

• FMN and FAD are covalently bound to proteins that funnel and distribute electrons.
• They accept two electrons and donate one electron at a time.

Properties of Cytochromes

• One-electron carriers with iron-coordinating porphyrin ring derivatives.
• Cytochromes are classified as a, b, or c based on ring additions.

Iron-Sulfur Clusters

• One-electron carriers that coordinate with cysteines.
• Contain an equal number of iron and sulfur atoms.

Properties of Coenzyme Q (Ubiquinone)

• Lipid-soluble dicarbonyl compound that easily accepts electrons.
• It accepts two electrons and picks up two protons to become ubiquinol.
• It is the mobile carrier that transports electrons between protein complexes.

Protein Components of the Mitochondrial Respiratory Chain

• Complex I:
  • NADH dehydrogenase
  • Mass: 850 kDa
  • Subunits: 45 (14)
  • Prosthetic Groups: FMN, Fe-S
• Complex II:
  • Succinate dehydrogenase
  • Mass: 140 kDa
  • Subunits: 4
  • Prosthetic Groups: FAD, Fe-S
• Complex III:
  • Ubiquinone: cytochrome c oxidoreductase
  • Mass: 250 kDa
  • Subunits: 11
  • Prosthetic Groups: Hemes, Fe-S
• Cytochrome c：
  • N/A
  • Mass: 13 kDa
  • Subunits: 1
  • Prosthetic Groups: Heme
• Complex IV:
  • Cytochrome oxidase
  • Mass: 204 kDa
  • Subunits: 13 (3-4)
  • Prosthetic Groups: Hemes; CuA, CuB

NADH: Ubiquinone Oxidoreductase (Complex I)

• Largest assembly in the mammalian cell.
• Contains over 40 polypeptide chains.
• Binds NADH on the matrix side
• Flavin mononucleotide accepts two electrons from NADH.
• Iron-sulfur centers pass one electron toward the binding site for ubiquinone.

NADH:Ubiquinone Oxidoreductase as a Proton Pump

• Accompanies transfer of two electrons from NADH to ubiquinone
• A transfer of protons from the matrix (N) to the intermembrane space (P)
• Experiments show about four protons are transported per one NADH.
• NADH + Q + 5H+N = NAD+ + QH2 + 4 H+p
• Reduced coenzyme Q picks up two protons.
• Protons are transported by proton wires.

Complex I Proton Pumping

• Electron flow alters the redox state of the protein complex.
• Induces resulting in conformational changes.
• The conformational change contributes to the linked oxidation/reduction cycle of coenzyme Q.
• The binding of Quinone induces a conformational change.
• When QH2 forms/releases, all 4 H+ are pumped from a single subunit.

Succinate Dehydrogenase (Complex II)

• FAD accepts two electrons from succinate.
• Electrons pass one at a time via iron molecules to ubiquinone, which becomes reduced.
• This complex does not transport proteins.
• Succinate dehydrogenase is a single enzyme performs two roles, it converts succinate to fumarate and donates molecules to the chain

Complex II Properties

• Distance for electrons to travel is approximately 40 Angstroms.
• Iron-sulfur cluster centers are less than 14 Angstroms
• Shorter distances facilitate faster electron transfer to coenzyme Q.
• Transfers one electron at a time from FADH2 to iron-sulfur clusters then to coenzyme Q
• 2 Hydrogens to Q from water
• Heme's role is unknown, hypothesis states it helps electron sink to prevent the formation of reactive oxygen species

Ubiquinone: Cytochrome c Oxidoreductase

• Uses two electrons from QH₂ to reduce two cytochrome c molecules.
• Contains iron-sulfur clusters, cytochrome b and c.
• Q-cycle translocates four additional protons to the intermembrane space.

Q Cycle

• Four protons are transported across the membrane per two electrons moved to cytochrome c .
• Two of the four protons come from the oxidation of QH2.
• Electrons travel split pathways.
• Q cycle explains how additional protons are picked up from the matrix.
• Subsequent QH₂ oxidizes second molecule to IMS, whilst one transforms regenerating, net transfer of ~four.

Cytochrome c notes

• A mobile electron carrier.
• Ubiquinone transports through membranes and cytochrome moves through the inner space layer
• Soluable.
• Can be either either Ferrous or Ferric. Carries from from bc1 to oxidase.

Cytochrome Oxidase (Complex IV)

• Complex consists of 13 subunits is a membrane protein.
• Copper ions include CUA and CUB: CUa accepts Cytc and Cub bonds with heme a3.

Complex IV (Cytochrome Oxidase): Electron Flow

• Four electrons reduce one O2 molecule into two H2O molecules.
• Matrix pulls four protons to it.
• Additional 4 protons from move to the intermembrane space.

Electron Transports Summaries

• Complex I: 1NADH + 11H+(N) + 1/2O2 -> NAD+ + 10H+(P) + H2O
• Complex II: FADH2 + 6H+(N) + 1/2O2 -> FAD + 6H+(P) + H2O
• The two different reactions represent the different number of protons transferred with ATP synthase

Respirasome: Protein Complex

• Consists of Complexs I, the III and IV
• Complex II can move around a lot

Reactive Oxygen Species

• Nicontinamide.
• Catalyzes multiple inner membrane actions.

Chemiosmotic Model: ATP Synthase

• Electron transport sets up H+ on the outside.
• Direct pumps occur.
• Potential and energy result in ATP synthesis

Mitochondrial ATP Synthase Complex Notes

ATP Synthesis requires multiple functional units.

• F1 soluble complex in matrix
  • Individually hydrolysis
• F0 integral membrane complex
  • Transports.
  • Transfers.

F1 Reaction Note

ADP and Pi leads to ATP

• Three ab-dimers.
• Open, loose and ties can exist.

Binding Model

Alpha and beta subunits contribute to reaction, fueled by 3 protons

Flow

• Glus get channels from A.
• Residues assist, subuint one roates with a new unprotonated glu
• results in 360 degree ratation

Proton Notes

• translocation leads to rotation and gamma which causes all the alpha beta subunit pairs to form in all three pairs

Transport

• Transfer occurs through various steps, facilitates mitochondrian reactions.

ATP yield

Occurs though glucose and other sources

Regulation

Primary control comes though various elements Inhitiion leads to cascade, etc

Notes on energy flow in cellular respiration, focusing on the role of carbohydrates, lipids, and amino acids as fuels. Explains chemiosmotic theory and energy coupling, highlighting the importance of proton gradients for ATP synthesis. Covers membranes for ATP synthesis in bacteria, mitochondria, and chloroplasts.