Gluconeogenesis diagram

Figure 21.20 Diagram of a tori q/de in a patient with a tumour. Lactate produced from glucose by tumour cells is converted back to glucose in the liver (gluconeogenesis) and released into the blood for re-uptake by tumour cell, an ATP-reguiring process. Note that muscle, immune cells and red blood cells will also contribute to the cycle (see. Chapter 6 Figure 6.10).

Figure 26-3. Schematic diagram of the interplay of fatty acid breakdown and ketone body formation with the synthesis (gluconeogenesis) and degradation of glucose (glycolysis). The P-oxidation of fatty acids provides the energy that drives the formation of glucose.

Fig. 31.5. Conversion of pyruvate to phosphoenolpyruvate (PEP). Follow the shaded circled numbers on the diagram, starting with the precursors alanine and lactate. The first step is the conversion of alanine and lactate to pyruvate. Pyruvate then enters the mitochondria and is converted to OAA (circle 2) by pyruvate carboxylase. Pyruvate dehydrogenase has been inactivated by both the NADH and acetyl-CoA generated from fatty acid oxidation, which allows oxaloacetate production for gluconeogenesis. The oxaloacetate formed in the mitochondria is converted to either malate or aspartate to enter the cytoplasm via the malate/aspartate shuttle. Once in the cytoplasm the malate or aspartate is converted back into oxaloacetate (circle 3), and phosphoenolpyruvate carboxykinase will convert it to PEP (circle 4). The white circled numbers are alternate routes for exit of carbon from the mitochondrion using the malate/aspartate shuttle. OAA = oxaloacetate FA = fatty acid TG = triacylglycerol.

The sequence of four enzyme reactions shown in the diagram below results in the removal of two pairs of hydrogen atoms from the fatty acyl CoA molecule which are passed to the cofactors NAD+ and FAD which become reduced to NADH and FADH2. As these reactions occur in the mitochondria, it is easy for the cofactors to be rapidly reoxidized by the electron transport process (the cytochrome chain) and this results in ATP synthesis. A molecule of acetyl CoA is produced per turn of the p-oxidation spiral. This acetyl CoA can be further metabolized to CO2, but cannot be used as a source of intermediates for glucose synthesis by gluconeogenesis. 

Figure 2. Diagram representing anaplerotic (solid lines and shapes) and cataplerotic (dashed lines and shapes) sequences connecting the Krebs cycle to gluconeogenesis, fatty acid metabolism, and dispensible AA synthesis. Some sequences can serve both anaplerotic and cataplerotic roles, thus linked metabolites (bold) can be catabolized or synthesized. a-KG, a-ketoglutarate OAA, oxaloacetate PEP, phosphoenolpyruvate.

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