This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Malate shuttle is important in ________ 
Select and explain. 
A. Glycolysis only, B. Glycogenolysis, C. Glycolysis and gluconeogenesis, D. Glycogen synthesis
C: Glycolysis and gluconeogenesis
Answer: C: Glycolysis and gluconeogenesis 
Explanation: NADH cannot penetrate the mitochondrial membrane, but it is produced continuously in the cytosol by 3-phosphoglyceraldehyde dehydrogenase, an enzyme in the glycolysis sequence.
The transfer of reducing equivalents is carried out by using the various shuttle systems.
Malate shuttle system is of more universal utility. Used to transport NADH from cytosol to mitochondria.
In glycolysis, the impermeable NADH produced in the cytosol are taken up into mitochondria for oxidation via malate shuttle.
In gluconeogenesis, pyruvate in the mitochondria yields impermeable oxaloacetate, which gets translocated to the cystol via malate shuttle for the sythesis of glucose.

Harper 30th edition  Pg-125,126,173