Metabolism | Transition Stage (Preparatory Phase)

📚 Premium Notes & Illustrations for Transition Stage: https://www.ninjanerd.org/lecture/transition-stage-preparatory-phase-2

Ninja Nerds!
In this metabolism lecture, Professor Zach Murphy guides you through the Transition Stage—also known as the Preparatory Phase—which links glycolysis to the citric acid cycle (TCA cycle). This critical step involves the conversion of pyruvate to acetyl-CoA and represents a key metabolic crossroads for carbohydrate, fat, and protein catabolism.

We begin by reviewing how pyruvate, the end product of glycolysis, is transported into the mitochondria and converted by the pyruvate dehydrogenase complex (PDC) into acetyl-CoA, with the release of CO₂ and the production of NADH. The structure, subunits, and cofactors of PDC—thiamine (B1), lipoic acid, CoA, FAD, and NAD⁺—are discussed in detail, along with how this multienzyme complex is tightly regulated.

You’ll learn about the allosteric and covalent regulation of pyruvate dehydrogenase, including the roles of PDH kinase and PDH phosphatase, as well as how hormonal signals like insulin and glucagon influence its activity in different tissues.

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