ATP

Glycolysis

  • Chemical Carbon Overview:

    • Six carbon molecules are processed without losing any carbon.

    • Focus is on breaking chemical bonds.

  • First Half of Glycolysis (Energy Investment Stage):

    • Spend two ATP.

    • The expenditure of ATP helps overcome energy inactivity requirements to split glucose.

    • Glucose is split into two three-carbon molecules called G3P (Glyceraldehyde-3-phosphate).

  • Second Half of Glycolysis (Energy Payoff Stage):

    • Each G3P produces:

    • 2 ATP

    • 1 NADH (electron carrier)

    • Conversion of G3P leads to the production of pyruvate.

    • Total ATP calculation:

    • Spent: 2 ATP

    • Produced: 4 ATP

    • Net Yield: 4 ATP - 2 ATP = 2 ATP

    • Total electrons accounted from NADH generation.

  • Molecular Overview:

    • Conservation of Carbon:

    • Two G3P molecules (3 carbons each) lead to 6 total carbons at input.

    • Resulting two pyruvate molecules exit as well.

    • Important note: do not focus on functional groups, only on carbons, energy, and electrons.

Pyruvate Oxidation

  • Process of Pyruvate Oxidation:

    • Defined as the loss of electrons (oxidation) leading to NADH generation.

    • One carbon exits as carbon dioxide (CO₂) for each pyruvate oxidized.

    • Total loss: 2 CO₂ (one from each pyruvate).

    • Resulting molecule: Acetyl-CoA (2 carbon molecules remain after CO₂ loss).

  • Location:

    • Glycolysis occurs in the cytoplasm; pyruvate oxidation takes place in the mitochondria.

Citric Acid Cycle (Krebs Cycle)

  • Entry and Output:

    • Input: two Acetyl-CoA molecules.

    • Outputs:

    • 4 CO₂ (2 from each acetyl-CoA)

    • 3 NADH (per acetyl-CoA)

    • 1 FADH₂ (per acetyl-CoA)

    • 1 ATP (per acetyl-CoA)

    • Total per glucose: 2 ATP, 6 NADH, 2 FADH₂, and 4 CO₂ produced.

  • Metabolic Pathway Structure:

    • Continuous cycle as oxaloacetate regenerates for following cycles.

    • Acetyl-CoA (2 carbons) + oxaloacetate (4 carbons) = citrate (6 carbons).

    • Series of reactions produce isocitrate (isomer), alpha-ketoglutarate (5 carbons), and succinyl CoA (4 carbons)—involves CO₂ release and NADH generation.

Total Energy Yield Calculation

  • Energy Summary Up to Citric Acid Cycle:

    • Total CO₂ generated: 6

    • Total ATP produced/net: 2

    • Total NADH generated: 10 (2 from glycolysis, 2 from pyruvate oxidation, 6 from the citric acid cycle)

    • Total FADH₂: 2

Electron Transport Chain (ETC)

  • Structure:

    • Comprised of four complexes (I-IV) located in the mitochondrial inner membrane.

  • Function:

    • NADH and FADH₂ deliver electrons to the chain; 10 NADH and 2 FADH₂ contribute a total of 24 electrons.

    • NADH transfers electrons to Complex I, and FADH₂ transfers to Complex II.

    • Electrons sequentially move through complexes I, II, III, and IV, eventually reducing oxygen, which acts as the final electron acceptor, forming water.

  • Energy Process:

    • Movement of electrons through complexes allows active transport of hydrogen ions (H⁺) across the membrane, creating a proton motive force (concentration gradient).

    • Facilitated diffusion occurs as H⁺ ions flow back through ATP synthase, driving ATP synthesis.

  • ATP Generation:

    • Process of chemiosmosis—movement of ions across an electrochemical gradient to generate ATP.

    • Total ATP yield heavily relies on the electrons captured in NADH and FADH₂ molecules.

  • Final Output of Aerobic Respiration:

    • The full cycle yields substantial ATP through substrate-level phosphorylation and oxidative phosphorylation.

    • Final production includes all previous calculations of NADH and FADH₂ leading to a final ATP tally, significantly maximizing energy capture from glucose.

Noteworthy Concepts to Remember

  • Isomerization: The conversion of citrate to isocitrate involves no loss of carbon but rearrangement of atomic structure (isomer formation).

  • Redox reactions: Oxidation (electrons lost) and reduction (electrons gained) processes are essential, specifically in linking glycolysis to the citric acid cycle and beyond.

  • Cofactors and Coenzymes: Essential for facilitating biochemical reactions involving electron transport; organic cofactors are crucial for metabolic pathways.

  • Energetic Overview: Follow each step's energy changes and transformations as they occur throughout cellular respiration, connecting earlier stages to later ones, supporting total energy yield understanding.

  • Regulatory Principles: Recognize that maintaining the concentration gradient during active transport is crucial for the chemiosmotic production of ATP, using principles of thermodynamics to reinforce cellular metabolism.

  • Overall Objective: Understanding that cellular respiration is a series of interconnected processes where carbon and energy (ATP) flow from glucose intake to complete oxidation, culminating in the production of CO₂ and water.