NADH produced in glycolysis is often called \"cytoplasmic NADH\" (or, better, I
ID: 879676 • Letter: N
Question
NADH produced in glycolysis is often called "cytoplasmic NADH" (or, better, I think, "cytosolic NADH"). It has to get into mitochondria to be oxidized in oxphos. But there is a problem: the inner mitochondrial membrane is impermeable to NADH.
Which of the following is true about the mechansm(s) by which cytosolic NADH provides electrons (in the form of NADH or QH2) for entry into oxphos?
A. NADH is directly transported in some organs across the inner mitochondrail membrane, by facilitated diffusion.
B. NADH is taken up directly, at the expense of 1 ATP per NADH, into the mitochondrial matrix by active transport.
C. Malate (formed by reduction of oxaloacetate by NADH) moves across the inner mitochondrial membrane, into the matrix, where oxidation of malate to oxaloacetate produces NADH, which enters electron transport.
D. Cytosolic NADH cannot contribute, directly or indirectly, to electron transport.
Explanation / Answer
C. Malate (formed by reduction of oxaloacetate by NADH) moves across the inner mitochondrial membrane, into the matrix, where oxidation of malate to oxaloacetate produces NADH, which enters electron transport.
The malate-aspartate shuttle (sometimes also the malate shuttle) is a biochemical system for translocating electrons produced during glycolysis across the semipermeable inner membrane of the mitochondrion for oxidative phosphorylation in eukaryotes. These electrons enter the electron transport chain of the mitochondria via reduction equivalents to generate ATP. The shuttle system is required because the mitochondrial inner membrane is impermeable to NADH, the primary reducing equivalent of the electron transport chain. To circumvent this, malate carries the reducing equivalents across the membrane.
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