Biochemistry in Tables, Schemes, and Graphs - S.D. Zhamsaranova 2009

Energy Metabolism
Biological Significance of the Tricarboxylic Acid Cycle

1. The TCA cycle is the major source of ATP. Energy for the synthesis of large amounts of ATP is provided by the complete breakdown of Acetyl-CoA to CO₂ and H₂O.

2. The TCA cycle serves as a universal terminal stage for the Catabolism of all classes of substances.

3. The TCA cycle plays a crucial role in anabolic processes via its intermediates:

Class="center">REGULATION OF ENERGY METABOLISM

ATP Synthesis in The Cell is regulated by energy demand, which is achieved through the coordinated control of reaction rates in the ETC and the common catabolic pathway (CCP).

An increase in ADP concentration accelerates NADH oxidation in the ETC, leading to an increased rate of Reactions Catalyzed by regulatory NAD⁺-dependent Enzymes, as well as an overall acceleration of the common catabolic pathway. In addition, ADP allosterically activates regulatory Enzymes of the CCP. Such Coordinated regulation of the ETC and CCP ensures that an adequate number of new ATP molecules is synthesized to replace those consumed; the greater the ATP consumption, the higher The rate of its synthesis.

The rate of the common catabolic pathway is regulated at the level of 4 reactions catalyzed by:

1) the Pyruvate dehydrogenase complex;

2) citrate synthase;

3) isocitrate dehydrogenase;

4) the $\alpha$-ketoglutarate dehydrogenase complex.

ENERGY INDICES UNDER VARIOUS PHYSIOLOGICAL CONDITIONS

Regulation of the COMMON CATABOLIC PATHWAY