Part II: Core Metabolism
Harvesting Chemical Energy
Plants, like all aerobic organisms, extract chemical energy from carbohydrates through glycolysis and the TCA cycle, feeding electrons into the mitochondrial electron transport chain to synthesize ATP. Unlike animals, plants also have unique metabolic adaptations including the alternative oxidase (AOX), multiple routes for glycolysis (plastidial and cytosolic), and specialized connections between photosynthesis and respiratory metabolism.
Lipid biosynthesis in plants occurs primarily in the plastid (de novo) and is subsequently modified in the endoplasmic reticulum. Plant-specific desaturases produce the polyunsaturated fatty acids characteristic of membranes and seed oils.
~30 ATP
per glucose (aerobic respiration)
2 per cell
Mitochondrial complexes shared with animals
~20%
Seed dry weight as storage lipid (oilseeds)
Chapters in Part II
Chapter 4: Glycolysis & TCA Cycle
All 10 glycolytic steps with enzymes and equations, pyruvate dehydrogenase complex, 8-step TCA cycle, anaplerotic reactions, allosteric regulation.
Chapter 5: Mitochondrial Electron Transport
Complexes I–IV, redox potentials, ubiquinone and cytochrome c, proton pumping, ATP synthase rotary mechanism, P/O ratio, plant-specific alternative oxidase and uncoupling proteins.
Chapter 6: Lipid Biosynthesis
Acetyl-CoA carboxylase, FAS complex, malonyl-CoA pathway, plastidial vs cytosolic routes, desaturases (FAD2/FAD3), triacylglycerol assembly (Kennedy pathway), galactolipids (MGDG/DGDG).
Key Reactions in Part II
Pyruvate kinase: \(\text{PEP} + ADP \rightarrow \text{pyruvate} + ATP\quad \Delta G^{\circ\prime} = -31.4\text{ kJ mol}^{-1}\)
TCA net: \(\text{Acetyl-CoA} + 3\,NAD^+ + FAD + ADP + P_i \rightarrow 2\,CO_2 + 3\,NADH + FADH_2 + ATP\)
Palmitate synthesis: \(8\,\text{Acetyl-CoA} + 7\,ATP + 14\,NADPH \rightarrow \text{palmitate} + 8\,CoA + 14\,NADP^+ + 7\,ADP\)