Aerobic Respiration Notes

Cellular respiration includes (catabolic pathway) is the process where cells break down food to release energy and make ATP.

Aerobic Respiration Overview

• Cellular respiration: Catabolic pathways for ATP production.

• Overall reaction: Summary of reactions.

• ATP: Primary energy source for all organisms (except chemoautotrophs).

• Aerobic respiration: Catabolic pathways needing $O_2$.

Redox Reaction

• Glucose carbons oxidize to $CO_2$ (lose e-, H, O).

• Oxygen reduces to $H_2O$ (gains e-, H, O).

• LEO says GER (Lose Electrons Oxidation, Gain Electrons Reduction).

Oxidation of Glucose

• Combustion: large Ea requires, rapid loss e energy release all once as heat.

• Cells oxidize glucose in steps, remove small # transfer $e^-$ to $NAD^+$.

ATP Production

• Phosphorylation: Adding phosphate to an organic compound.

• Substrate-level phosphorylation: a phosphate group is directly transferred from molecule (a substrate) to ADP to form ATP; no $O_2$.

• Oxidative phosphorylation: Electrochemical gradient phosphorylates ADP to atp ; uses $O_2$.

• Substrate-level phosphorylation: Phosphate transfer from substrate to ADP by kinase enzymes.

• Oxidative phosphorylation:using energy from the electron transport chain to phosphorylate adp n make atp O2 is involved

Stages of Aerobic Respiration

1. Glycolysis: Cytosol.

2. Pyruvate Oxidation: Mitochondria matrix.

3. Krebs Cycle: Mitochondria matrix.

4. Oxidative Phosphorylation: Mitochondria.

• Aerobic Respiration requires $O_2$.

• Result: 1 glucose yields 36 ATP (eukaryotes) or 38 ATP (prokaryotes)

• Locations of aerobic : Cytoplasm & Mitochondria

Glycolysis

• Location: Cytosol.

• Enzymes: 10 total.

• Glucose (6C) splits into 2 pyruvate (3C).

• Net 2 ATP by substrate-level phosphorylation.

• Glucose carbons oxidized, $2NAD^+ \rightarrow 2NADH$ (reduced).

• Anaerobic; no $O_2$ needed.

• Net energy payoff: Glucose + $2NAD^+$ + 4e + 4$H^+$ --> 2 Pyruvate + $H_2O$ + 2 NADH + 2$H^+$

• Dehydrogenase: Catalyzes redox reactions btw substrates (e- transfer).

  • Ex: $NAD^+$ + 2e- + $H^+$ → NADH

• Kinase: Catalyzes phosphorylation reactions (phosphate transfer).

  • Ex: glucose + Pi → glucose-6-phosphate

• Isomerase: Catalyzes isomerization reactions (rearrangement).

  • Ex: glucose-6-phosphate → fructose-6-phosphate

Mitochondria

• All stages after glycolysis in mitochondria.

• Intermembrane space: Accumulates protons.

• Matrix: Enzymes & pH for Krebs cycle.

• Inner membrane: ETC and ATP synthase.

• Outer membrane: Transport proteins for pyruvate.

• Cristae: Increases surface area.

Pyruvate Oxidation

• Location: Matrix.

• Enzyme: Pyruvate dehydrogenase.

• Pyruvate oxidized to $CO_2$.

• $NAD^+ \rightarrow NADH$ (reduced).

• Pyruvate (3C) becomes acetyl-CoA (2C).

Krebs Cycle

• Location: Mitochondrial matrix.

• Enzymes: One for each reaction.

• Acetyl-CoA (2C) joins oxaloacetate (4C) to form citrate (6C).

• Oxidation releases 2 $CO_2$.

• Electrons gained by $NAD^+ \rightarrow NADH$ and $FAD \rightarrow FADH_2$.

• Substrate-level phosphorylation produces ATP.

• Oxaloacetate regenerated; cycle continues.

• Net Reaction for 1 Acetyl-Co: Acetyl-CoA + 3 $NAD^+$ + FAD + ADP + Pi 🡪 2$CO2$ + 3NADH + $FADH2$ + ATP

• Net Reaction X2 (for one glucose): 2Acetyl-CoA + 6 $NAD^+$ + 2FAD + 2ADP + 2 Pi 🡪 4$CO2$ + 6NADH + 2$FADH2$ + 2ATP

• Glucose carbons fully oxidized into $CO_2$.

Oxidative Phosphorylation

• Couples NADH and $FADH_2$ oxidation by ETC with ATP synthesis.

  1. Electron Transport Chain

  2. Chemiosmosis

Electron Transport Chain

• Proteins in inner mitochondrial membrane transfer electrons and protons ($H^+$).

• Each complex more electronegative.

• Electrons from NADH & $FADH_2$ pass through chain.

• Oxygen is final electron acceptor, forming water.

• Four protein complexes:

  • Complex I - oxidizes NADH

  • Complex II - oxidizes $FADH_2$

  • Complex III

  • Complex IV

• Two mobile e- shuttles:

  • Ubiquinone (UQ or Q): Shuttles e- from complex I/II to III.

  • Cytochrome c (cyt c): Transfers e- from complex III to IV.

• Component electronegativity increases along chain.

• $O<em>2$ strongest pull, NADH & $FADH</em>2$ weakest.

• Electrons pulled through chain towards $O_2$.

Chemiosmosis

• Energy released during each transfer in ETC. transporting H protons from matrix to intermembrane space

• Each NADH = ~10 $H^+$ pumped.

• Each $FADH_2$ = ~6 $H^+$ pumped.

• High [$H^+$] in intermembrane space creates proton gradient.

• Complexes I, III, IV transport $H^+$.

• $FADH_2$ bypasses Complex I, fewer $H^+$ transported.

• Electrochemical gradient:

  • Chemical: concentration gradient.

  • Electrical: $H^+$ charge repels/attracts.

• Proton-motive force: a force drives proton movement.

ATP Synthase

How H⁺ Ions Help Make ATP (Chemiosmosis & ATP Synthase)

• H⁺ ions flow along their concentration gradient (high → low).

• They move through a channel in ATP synthase (from intermembrane space → matrix).

• This movement is driven by the proton-motive force.

• As H⁺ ions pass through, they cause the head of ATP synthase to rotate.

• This rotation catalyzes the formation of ATP from ADP + Pi.

• 3-4 $H^+$ needed per ATP.

• 1 NADH = 10 $H^+$ = 3 ATP.

• 1 $FADH_2$ = 6 $H^+$ = 2 ATP.

Total ATP Yield

• Total net ATP = 38 (36 in eukaryotes)

• Actual yield may be lower.

• Inexact NADH/$FADH_2$ to ATP ratio.

• $H^+$ flow energy loss.

• NADH transport cost.

• Closer to 30 ATP/glucose.

Efficiency of Aerobic Respiration

• Glucose: 2870kJ/mol energy.

• 38 ATP x 31kJ/mol = 1178kJ/mol

• Efficiency ~ 41%.

• Rest dissipated as thermal energy.

• Better than most human-designed devices!

Interconnection of Metabolic Pathways