page 584 glycolysis and tca cycle: final accounting based on ~2.5 atp/nadh and 1.5 atp/fadh2 ~32...

Page 584

Glycolysis and TCA cycle: final accounting

• based on ~2.5 ATP/NADH and 1.5 ATP/FADH2• ~32 ATP/(glucose oxidized to 6CO2)

Text – Figures, pg. 584

Free Energies for TCA Reactions

• note necessity of low (i.e. large negative) G for citrate synthase to drive preceding malate dehydrogenase reaction. This results in low oxaloacetate concentration.

• large negative G steps are points of regulation.*

***

Figure 17-15

Regulatory Mechanisms in Pyruvate Dehydrogenase and the TCA Cycle

• covalent modification of enzymes ex: phosphorylation of pyruvate dehydrogenase

• (non-covalent) product and feedback inhibition (e.g. by NADH, ATP, citrate)

• allosteric effectors (ADP/ATP, Ca++)

Figure 17-16

Points of Regulation in the TCA Cycle

inhibition

activationText – Figure 17-16

Figure 17-17

TCA Cycle intermediates are a major source of molecules for other metabolic pathways

• note that several of the molecules look like amino acids, except for the absence of an -amino group

Text – Figure 17-17

Page 589

TCA Cycle intermediates are a major source of molecules for other metabolic pathways

ex: production of glutamate from -ketoglutarate

Production of some other amino acids by transamination reactions

ex: production of alanine and -ketoglutarate from glutamate and pyruvate

Page 589

Production of some other amino acids by transamination reactions

ex: production of aspartate and pyruvate from oxaloacetate and alanine

Page 590

The depletion of TCA cycle intermediates for use in other pathways must be offset by replenishing (anaplerotic) reactions, including pyruvate carboxylase.

Text – Figure, pg. 590