Question

Glycolysis produces NADH. However, NADH cannot cross the inner mitochondrial membrane to be used in the electron transport chain (respiratory chain). The malate-aspartate shuttle in some animal cells transfers electrons from cytosolic NADH to the matrix. A diagram of the malate-aspartate shuttle is given below. You can use it as a reference to answer parts (a) and (b)

a) Which compound accepts electrons from NADH, producing a compound that can pass through the inner membrane?
A. glutamate
B. aspartate
C. α- ketoglutarate
C. oxaloacetate
b) Which compound transfers reducing equivalents (electrons) into the mitochondrial matrix? O
A. malate
B. α-ketoglutarate
C. oxaloacetate
D. glutamate
E. aspartate

Answer 1

a) Oxaloacetate.

b) Malate.

Step-by-step explanation:

The malate-aspartate shuttle works in the mitochondria of the liver, kidney, and heart.

The cytosolic NADH reducing equivalents transfer to the cytosolic oxalacetate, producing malate, by the cytosolic malate dehydrogenase. This malate crosses the inner mitochondrial membrane throughout the malate-α-ketoglutarate transport system.

Inside the matrix, the reducing equivalents pass from the malate to the NAD⁺, forming NADH, by the action of the mitochondrial malate dehydrogenase. This formed NADH passes electrons directly to the respiratory chain.