Question

Glycolysis

1. How are reducing equivalents from NADH generated in glycolysis in the cytoplasm transported into the mitochondrion resulting in the formation of NADH within the inner mitochondrial membrane?

Thank you, I'm having trouble locating this answer in my notes/text book

Answer 1

The glycolytic pathway is the primary source of NADH formation. NADH synthesized during the glycolytic process finally transfers the the electrons two electron transport chain. But, NADH cannot cross the the inner mitochondrial membrane. So two different shuttle systems help in transfer of electrons from NADH to the electron transport chain.

1 The malate-aspartate shuttle is the principal mechanism for the movement of NADH from the cytoplasm into the mitochondrial matrix. The electrons are carried into the mitochondrial matrix in the form of malate. Cytoplasmic malate dehydrogenase reduces oxaloacetate to malate while oxidising NADH to NAD+. Malate then enters the mitochondrial matrix, whether reverse reaction is carried out by mitochondrial malate dehydrogenase and the regeneration of NADH occurs.

Fig:- Malate- aspartate shuttle

2. Glycerol 3- phosphate shuttle

In in glycerol 3- phosphate shuttle electrons from NADH can enter the mitochondrial electron transport chain by being used to reduce dihydroxyacetone phosphate to glycerol 3-phosphate. Glycerol 3- phosphate is reoxidised by electron transfer to an FAD prosthetic group in a membrane bound glycerol 3- phosphate dehydrogenase. FADH2 subsequently transfers electrons to Q to form QH2, which allows these electrons to enter the electron transport chain.

Fig:- Glycerol 3- phosphate shuttle