Thanks for stopping by. This is Two Minute Classroom and today we're doing an overview of cellular respiration. This will be a good introduction to the topic or a good refresher before a test or homework assignment.
Cellular respiration is the process by which your cells break down macromolecules, like glucose, to produce ATP, the energy currency of the cell. There are three main steps in cellular respiration. Glycolysis, the Krebs or citric acid cycle, and the electron transport chain, also known as oxidative phosphorylation. We'll cover each of these steps briefly in this video and focus on the total ATB produced from a single glucose molecule going through each step.
You can find links for a more detailed video of each step in the description below once they are produced. The first step, glycolysis, is a series of reactions that take place in the cytosol. Glucose is a high energy molecule and glycolysis starts the process of extracting that energy from the glucose molecule.
Glycolysis requires the input of a glucose and two ATP molecules and puts out four ATP, two NADH molecules, and two pyruvate molecules. So the net ATP production of glycolysis is two ATP. The two NADH will come into play later.
The two pyruvates then undergo oxidation to produce two acetyl CoA molecules, also producing two more NADH. These two acetyl CoAs go into the next step, the Krebs cycle. The pyruvate oxidation and Krebs cycle both take place in the mitochondria. Each acetyl CoA goes through the Krebs cycle separately and produces three NADH, one FADH2, and one ATP, or GTP.
Since this happens twice, Our total production in the Krebs cycle is 6 NADH, 2 FADH2, and 2 ATP. As stated earlier, the NADH and FADH2 will be used in the final step of cellular respiration. And this brings us to our final step, oxidative phosphorylation and the electron transport chain, or ETC, which also takes place in the mitochondria. Without getting too complex, This step utilizes the NADH and FADH2 to create a concentration of hydrogen ion and electrochemical gradient on one side of a membrane.
This sounds complicated, but just think of it like a dam holding a high concentration of water on one side. Our hydrogen ions are like the water. Just as the water pressure of a dam can push a turbine to create energy, the high concentration of hydrogen ions powers a pump to create ATP. The pub in this case is a very efficient enzyme called ATP synthase.
For each NADH that goes into the electron transport chain, we get approximately 2.5 ATP out. And for each FADH2, we get 1.5 ATP out. Looking at our totals for a single glucose molecule, we have 10 NADH, 2 from glycolysis, 2 from pyruvate oxidation, and 6 from the Krebs cycle.
which yields approximately 25 ATP in the final step of oxidative phosphorylation. We also have 2 FADH2 from the Krebs cycle, which produce 3 more ATP. And finally, we have 4 ATP molecules, 2 ATP from glycolysis and 2 ATP from the Krebs cycle, for a grand total of 32 ATP from a single glucose molecule. It's very important to note here that there is a theoretical yield of 38 ATP. But conditions in the cell put the actual yield between 30 and 32 ATP.
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Check out the links in the description for a free trial of Magoosh. Thanks for watching, and I'll catch you next time.