Figure 3.

Overview of catabolic pathways leading to mitochondrial ATP production.

Multiple pathways of substrate oxidation and reduction support energy transfer. Lipids (yellow) are broken down into glycerol backbone and fatty acids; carbohydrates (teal) are broken down into simple sugars and then glucose; and proteins (red) are broken down into monomeric amino acid units. Fatty acids, pyruvate, and many amino acids are transported into the mitochondria and undergo oxidation to fuel the tricarboxylic acid (TCA) cycle. Various metabolic intermediates such glycerol-3-phosphate (G3P) or proline can be transported into the mitochondria to fuel electron transport directly through the oxidative phosphorylation (OXPHOS) system independent of TCA cycle.