Now, there are actually different ways by which the NADH molecules can actually get into the mitochondria. And in this lecture, I'd like to focus on a specific type of membrane transport system known as the glycerol three phosphate shuttle. And this is the shuttle that is used predominantly by skeletal muscle cells of our body. So the inner mitochondrial membrane is actually impermeable to NAD plus or NADH molecules. And that means these NADH molecules, once formed in glycolysis, cannot simply move across the membranes of the mitochondria. And their movement basically depends on a specialized membrane transport system that we call glycerol three phosphate shuttle.