Question

2. Trace the pathway of electrons all the way from glucose to O2, through cellular respiration. Include events of inter-molecular energy transfer.

Answer 1

Aerobic respiration involves the catabolism of glucose to release the energy stored in the chemical bonds of glucose. This energy is captured to produce ATP from ADP + Pi (Oxidative phosphorylation).
It includes four major steps.
i. Glycolysis: Glucose to 2 Pyruvate
Net yield = 2 ATP and 2 NADH

ii. Transition reaction: 2Pyruvate to 2 Acetyl CoA
Net yield = 2 NADH

iii. TCA cycle: 2 Acetyl CoA to 4 CO2
Net yield = 6 NADH, 2 FADH2 and 2 ATP

iv. Electron transport chain:
Electrons from the respiratory substrates are captured by NAD+ and FAD which get reduced to produce NADH and FADH2. These reduced coenzymes bring these electrons to the electron transport chain and pass them to the electron carriers located in the inner mitochondrial membrane.
Molecular oxygen is the ultimate electron acceptor in aerobic respiration.
2H⁺ + 2e^- + 1/2 O₂ ----> H₂O

As electrons flow through ETC, protons are pumped across the membrane to generate a proton gradient which is coupled to produce ATP by ATP synthase complex.