Bioenergetics and Metabolism
What you must know
Understand free energy: reactions with negative ΔG are spontaneous (exergonic); positive ΔG is nonspontaneous (endergonic). ATP hydrolysis is exergonic and couples to endergonic reactions. Know glycolysis (glucose → 2 pyruvate, net 2 ATP, 2 NADH), the citric acid cycle (per acetyl-CoA: 3 NADH, 1 FADH2, 1 GTP/ATP), and oxidative phosphorylation (electron transport chain builds a proton gradient; ATP synthase uses it). Know fermentation regenerates NAD+ without oxygen. Understand that fatty acid beta-oxidation and amino acid catabolism feed into the same pathways. Recognize that NADH yields more ATP than FADH2 because it enters the chain at a higher-energy complex.
Traps
Questions may ask net versus gross ATP; count net (glycolysis yields net 2 ATP). Do not confuse the location of pathways (glycolysis in cytosol; TCA and ETC in mitochondria). Watch for claims that oxygen is the final electron acceptor in glycolysis-it is in the ETC.
Worked rule of thumb
Track electrons and protons: NADH/FADH2 carry electrons to the ETC; the proton gradient drives ATP synthase. If a question asks where a pathway occurs, anchor it to cytosol versus mitochondrial matrix/inner membrane.
Quick example
One glucose yields 2 pyruvate and net 2 ATP in glycolysis. Each pyruvate forms acetyl-CoA (producing NADH), which enters the TCA cycle to generate more NADH/FADH2 for the ETC.