Question

Gluconeogenesis

1. As part of the metabolic pathway for amino acid degradation, malate not oxalacetate is transported into the cytoplasm form the mitochondrion. Why malate?

2. Explain how carbon dioxide serves to couple ATP hydrolysis into the energetics of the synthesis of PEP to pyruvate? Provide both mechanism and energetics.

These two questions are from a study guide and I'm struggling finding the answers in my notes and text book, thank you for your help!

Answer 1

ANSWER 1 ) The malate-aspartate shuttle system, also called the malate shuttle, is an essential system used by mitochondria, that allows electrons to move across the impermeable membrane between the cytosol and the mitochondrial matrix. The electrons are created during glycolysis, and are needed for oxidative phosphorylation. The malate-aspartate shuttle is needed as the inner membrane is not permeable to NADH or NAD+, but is permeable to the ions that attach to malate. When the malate gets inside the membrane,the energy inside of malate is taken out by creating NADH from NAD+, which regenerates oxaloacetate. NADH can then transfer electrons to the electron transport chain.The reaction of malate dehydrogenase from malate to oxaloacetate possesses a free Gibbs energy of +29.7 kJ/mole, so the concentration of oxaloacetate is almost one million times lower than malate. A specific transporter would be physiologically not used because of the very low concentration of the oxaloacetate thus no oxaloacetate transport occur from mitochondria to cytoplasm instead malate is transported.