In this video, we're going to introduce the phases of glycolysis. It turns out that glycolysis actually consists of a series of a total of 10 chemical reactions. These 10 chemical reactions that make up glycolysis can actually be grouped into 2 phases. In this video we're not really going to focus on the 10 reactions so much, but we are going to focus on how these 10 reactions are grouped into 2 phases, and we're really going to be focusing on the 2 phases of glycolysis. The first phase of glycolysis is called the energy investment phase, and the second phase of glycolysis is called the energy harvest phase. Notice that the energy investment phase up above is color coordinated to the energy investment phase down below, and the energy harvest phase is color coordinated to the energy harvest phase down below. Notice in this image down below, really what we're showing you is glycolysis. Notice that it's starting with a single glucose molecule that has 6 carbon atoms, and it breaks down that glucose into 2 pyruvate molecules each with 3 carbon atoms. This whole green box represents glycolysis, but once again glycolysis occurs in 2 phases, the energy investment phase and the energy harvest phase. The energy investment phase, as its name implies with the investment, is going to require an investment of energy or an input of energy by using 2 ATP molecules. This is a little bit ironic because if you recall from our previous lesson videos, the whole point of aerobic cellular respiration is to make a lot of ATP. But the very first stage of aerobic cellular respiration, glycolysis, the very first thing that happens is that it does not make ATP, but it uses ATP. However, it turns out that this is just an investment of the ATP because by inputting 2 ATP molecules the cell is able to transition into the second phase of glycolysis which is the energy harvesting phase. As its name implies it's going to harvest energy or produce energy, specifically by forming 2 NADH molecules and 4 ATP molecules. If we take a look at our image down below at glycolysis, notice that the first phase of glycolysis, the energy investment phase, is actually going to use 2 ATPs and that is using some of the cell's energy. However, this is just an energy investment because after the cell utilizes those 2 ATPs, it can transition into the next phase here which is the energy harvest phase. The energy harvest phase notice produces 2 electron carriers, specifically 2 NADH molecules, and it also produces a total of 4 ATP molecules. Now, if we're looking at the net products from 1 single glucose molecule, then what we'll see is that not only are 2 pyruvates formed and 2 NADH are formed, but there's also a net of 2 ATP molecules that are formed. But wait a second, Jason. I thought you said that there were 4 ATP molecules that were made, not 2 ATP molecules. Well, what we need to remember is that 2 ATP molecules were being used up in the energy investment phase. So because 2 ATP molecules were used up, of the 4 ATP molecules that are being made, 2 of them are just making up for the 2 that were invested. And so really there's just a net of 2 ATP molecules made. If we take a look at this part of our image down below right here, we're reminding you that the energy harvesting phase does produce a total of 4 ATPs, as we indicated right here. However, we can't forget that the energy investment phase burns or uses 2 ATPs. So we have to subtract off those 2 ATPs from the total. And so that gives us a total net of 2 ATP molecules produced during glycolysis, 2 net ATPs made. An easy way to remember that there are 2 net ATP made during glycolysis is to remember that the net products from 1 glucose molecule are just double. You get not only 2 pyruvates but also 2 NADH, and also 2 net ATP molecules. The 2 pyruvates that are formed at the end of glycolysis end up getting transported to the mitochondrial matrix, basically getting transported to the mitochondria so that the next step of cellular respiration can take place. Notice that here glycolysis occurs once again on the outside of the mitochondria and it ends up producing 2 NADH, a net of 2 ATPs, and 2 pyruvates. These 2 pyruvates are going to make their way to the mitochondria and into the mitochondrial matrix. This here concludes our introduction to the phases of glycolysis, and we'll be able to get some practice applying these concepts as we move forward in our course. So I'll see you all in our next video.
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- 1. Introduction to Biology2h 40m
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- Introduction to Community Ecology2m
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8. Respiration
Glycolysis
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