Hey everybody Dr. O, I know metabolism and cellular respiration is complicated. In this video I am going to try to make it as manageable as possible by just showing you where the energy comes from. We’ll talk about the steps and the pathways more later. I just want to talk about what comes out of each of these four major areas okay, so let’s go ahead and start with glycolysis: “The big picture” you’re taking one six carbon glucose and slitting it in half. While you do that you are going to generate what is called a net gain of two ATP, and that’s because you had to spend two to make four. Uh but for now there is still a net gain of two ATP. This ATP has been produced, so in class I like to say, “this is money that I have in my hands.” But also, during glycolysis you now have made two NADH, so imagine we are at a casino and these NADHs are the chips and each of these NADH chips is worth three dollars or three ATP. So, after glycolysis, I have a net gain I’ve made two ATP two that I can spend right now, but I also have the ability to make six more ATP when I take it to the “cashier.” The cashier is going to be our electron transport system. Alright, so in the presents of oxygen now we move on we split glucose in half into those two three-carbon pyruvates. Now we take them causing a transformation step which I like to call the “intermediate step.” Where you take your two three-carbon pyruvates and turn them into two-carbon acetyl CoA. So, during this intermediate step you have produced zero ATP, so we still only made the two dollars. The two ATP in our pocket, but we made two more NADHs so now we have two ATP, and we now have four NADHs which gives us the ABILITY to make twelve more ATP. So just keep track of what’s in your two pockets we have two ATP and four NADHs. Then we go to “the Krebs cycle” the Krebs cycle is very complicated and doesn’t generate much energy it generates just two ATP total, but this is where we get most of our electrons this is where we do most of our “harvesting” and we make most of our “chips” that we’ll cash in. So, here at the Krebs cycle also known as the citric acid cycle, TCA cycle lots of names but at the Krebs cycle you must go through it twice that’s why each run through the cycle only makes one ATP but remember we split glucose in half so you’re going to go through it two times. So, you’re going to generate two ATP, but we are now going to generate six more NADHs and two FADH2. So NADH is the electron carrier made from niacin and each one of those is worth three ATP. FADH2 is the electron carrier made from riboflavin and each is only worth two, so let’s do our running totals now and see where we are at. So, we’re ready to walk up to the cashier remember the cashier in my example is the electron transport system. We have made four ATP potentially we have made four dollars money in our hands ATP that can be used, but we now have ten NADHs we got two during glycolysis, two during the intermediate step, and six here during the Krebs cycle so those are going to be worth a total of thirty ATP, and we also have two FADH2s that are worth two ATP a piece for a total of four. So now, we go to our electron transport system and yes, we have made a hand full of energy, but here is where we are going to make 34 more ATP and remember why ten NADHs are going to be worth a total of thirty uhm two FADH2s are worth a total of four. So, we made our two ATP in glycolysis, and we made zero in the intermediate step, and we made two during the Krebs cycle. This is what gives you a maximum production of 38 ATP. So we’re talking about prokaryotes we’re talking about bacteria it would be 38 if they can fully oxidase glucose they would make 38 ATP but you look at the screen here you see that the electron transport system or the whole system the cellular respiration pathways only leads to 36 ATP per glucose in humans and here is why: notice that minus two for the NADH transport cost, here’s how I like to think about that- - we make a net gain of two ATP during glycolysis just like bacteria do. We must spend two ATP to get these building blocks into the mitochondria remember the mitochondria is the powerhouse of the human cell uh the site of ninety-five percent of ATP production. It is a very important organelle, but it cost money to use it. So, we make 38 ATP just like bacteria do but we have to spend two and they don’t and that is why I ask you depending on the class you’re in. If you fully oxidase glucose in a human, you’re going to get 36 ATP in a bacterium it is going to be 38 and that’s why. This image here just kind of shows it here in bacteria without subject those two ATP the maximum amount of ATP you can get by fully metabolizing glucose would be 38 then all the same numbers would apply there. Uhm, now we say theorical yield because this is way messier than this. Some cells are going to produce less some are going to produce a lot less, but this is the textbook example of how much energy can be produced when you fully metabolize and fully oxidize glucose. Alright so that’s all the key players and that’s where the energy comes from in the four steps: glycolysis, the intermediate step, the Krebs cycle, and at the end the electron transport system. I hope this helps we’ll dive deeper in other videos have a wonderful day and be bl