Hi. In this video, we're going to be talking about gluconeogenesis and metabolic regulation. So first, let's talk about gluconeogenesis. This is a fancy word, it's kind of complicated, but essentially, it's just a metabolic pathway that is responsible for synthesizing glucose from pyruvate. Remember, pyruvate is the end product of glycolysis. Gluconeogenesis uses pyruvate to sort of go backwards from glycolysis and create glucose. So when is this used by the body? This is used when glucose stores are depleted. There's not enough glucose, none is coming in; therefore, your body needs to synthesize it so that it has the energy, and can use it for energy and other processes. But it's not the easiest thing to do because the synthesis of gluconeogenesis requires energy. Every time you create a glucose molecule it's actually going to use 4 ATP and 2 GTP. That's kind of a lot of energy, but it ends up being worth it because, if glucose can eventually turn into 36 ATP if it's processed in the presence of oxygen. So, eventually, you do get that energy back, but it does require a lot of energy to create it.
Now, like I said, this runs almost, and the keyword here is almost in reverse of glycolysis. Glycolysis has 10 steps, there are 10 steps in gluconeogenesis, but it's not the exact reverse. The reason is that 3 steps in gluconeogenesis have to be different, compared to glycolysis. These 3 steps, which are steps 1, 3, and 10 of glycolysis, are just so exergonic, which means that when they're running in glycolysis, they release so much energy, they actually can't be reversed. The cell cannot overcome the amount of energy it would need to run those reactions in reverse. So instead, it sort of bypasses them.
I'm going to go over the 3 steps that are different between gluconeogenesis and glycolysis. The first is going to be step 10 of glycolysis. So this would be step 1 of gluconeogenesis. What happens here is CO2 gets added, and phosphate gets added to pyruvate. So, the important thing here is because this is step 10 of glycolysis, we're starting with pyruvate and it uses ATP, uses CO2, and uses GTP to create this molecule. That's the first step of gluconeogenesis, which is the 10th of glycolysis. Then, step 7 of gluconeogenesis is the same as step 3 of glycolysis. What happens is the removal of a phosphate. So you have 2 phosphates here, one gets removed, you're left with just 1, and this happens again in step 10, where there's 1 phosphate, it gets removed and you end up with the byproduct here of glucose. The rest of the steps are exactly the same as glycolysis just running in reverse. So if you're, you won't need to necessarily know all the steps of gluconeogenesis in order, just know that there are 3 that differ because they can't overcome the energy and what they do is they just sort of bypass that through the use of different enzymes. So with that, let's now move on.