All right so we have gone from Glycolysis to Fermentation, then if there’s oxygen, we continue on with the the Transition Reaction and the Kreb’s Acid Cycle and now we’ve come to the final series of reactions to create the most ATP called the Electron Transport System! From complete aerobic cellular respiration, we turn a glucose of sugar into 6CO2 and 6H2O’s and our net gain is 30-38 ATP.
See how important it is to have oxygen?
Many bacteria, which are tiny, simple cells can live wonderful lives without the need for oxygen. They could survive on these very low amounts of ATP. Complex, human cells like brain cells cannot survive on low ATP. When brain cells aren’t getting oxygen, start counting the seconds cause you only have 4 minutes for those brain cells to live. Human cells are much more energy intensive.
Okay, so let’s move on…
Electron Transport Phosphorylation Chain aka Oxidative Phosphorylation aka Chemiosmotic ATP synthesis
Before we continue here’s an analogy!
We’re going to play the HOT POTATO GAME.
Imagine ten of you are lined up in a row and we have a BBQ with potatoes wrapped in aluminum foil grilling on the BBQ. Imagine I throw the hot potato at you and you have to throw it to the next person. Since this is a hot potato that is getting tossed, it’s giving off heat. So what’s this have to do with the respiration?
What’s lined up here is not a row of people but a row of coenzymes (vitamins and minerals) and they’re going to toss these “hot potato” hydrogens off to each other. They haven’t been taken off a bbq grill but they have been taken off a sugar molecule. The reason they are high energy “hot potato” electrons are because they are traveling at high energy orbits. These hydrogens are going to get passed from one coenzyme to the next, giving off energy, just like a hot potato would give off heat and that energy is going to be used to attach Phosphate onto ADP to form ATP (called phosphorylation). There’s enough energy flow here to generate 34 ATP because of all the energy that’s being released from these hydrogens.
At the end of the line, the cooled off hydrogens are attached to oxygen and what happens when you do that? It forms water. So we see that it’s in this last series of reactions where most of the ATP is generated and finally the cooled down hydrogens attach to oxygen so we finally dispose of the hydrogen ions so it doesn’t affect the acidity.
Overall this is called oxidative phosphorylation. Oxidative, because oxidation is a loss of H+ and e- and we are getting rid of hydrogens and using the energy to phosphorylate ADP (add a phosphate to ADP) to create ATP.
Here’s the slightly more complicated version:
Remember that the krebs cycle that we left off on, occurred inside the mitochondria.
A mitochondria consists of an inner membrane and an outer membrane. Right between the inner membrane and outer membrane is the outer compartment. The coenzymes are located in the inner compartment of the mitochondria while the electron transport system is located right on the inner membrane. As those coenzymes transfer those hydrogens, they transfer them to the outer compartment of the mitochondria so you get a real high concentration of hydrogen atoms in the outer compartment (in between the inner and outer membranes).
Again, the Electron Transport System consists of a series of coenzymes finally concentrating hydrogens in outer part of the mitochondria.
Those hydrogens diffuse, like all diffusion occurs from a high concentration to a lower one, from the outer to the inner space. As they flow down their gradient into the inner compartment, they activate ATPsynthase that uses this flow of hydrogens to phosphorylate ADP into ATP.
This idea of the flow of hydrogens is commonly explained like a river. When water is flowing across a river it’s going from a higher elevation to a lower elevation. If you put a water wheel in the middle of that flow, you could use the turning of the wheel to do work for you. As these hydrogens flow “down stream” they release usable energy. This is known as the chemiosmotic model of the mitochondria.
There’s various ways to calculate how many ATP’s you get. Newer studies show that the numbers I’m gonna give you are smaller. We used to say for each NAD that transfers hydrogens and electrons that we get 3 ATP’s. If we get 3 per NAD and we have 10 NAD’s, that’s 30 ATP’s. For each FAD that transfers hydrogens, we get 2 ATP’s, so that’s 4 ATP’s. So that’s 34 ATP’s. Nowadays instead of 3 it’s said to be 2.5 ATP per NAD’s.
Incidentally I could explain these in very sophisticated or very simple versions. We all need to do this because as a future health care professional, when we’re talking to other physicians and nurses, we need to speak in sophisticated ways but when we speak to patients, we must speak in simplified ways.
- Anabolic and Catabolic Reactions
- Intro to Cellular Respiration: The Production of ATP
- How Glucose Levels are Regulated in the Blood Stream
- Cell Respiration Part 1: Anaerobic Respiration (Glycolysis and Fermentation)
- Cell Respiration Part 2: Aerobic Respiration (Transition Reaction & Kreb’s Citric Acid Cycle)
- Cell Respiration Part 3: Aerobic Respiration (Electron Transport System)
- The Catabolism of Fats and Proteins for Energy
- The Catabolism of Nucleic Acids
- Oxygen Debt