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Aerobic Respiration

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Aerobic respiration is the process of producing cellular energy involving oxygen. Cells break down food in the mitochondria in a long, multistep process that produces roughly 36 ATP. The first step in is glycolysis, the second is the citric acid cycle and the third is the electron transport system.

Aerobic respiration is the process of breaking down the food that comes into a cell using oxygen to help power that process. A cell would do this in order to generate a lot of ATP now the basic chemical reaction is C6H12O6 that's glucose plus 6O2 and that's oxygen gas yielding 6 carbon dioxide gas molecules which eventually diffuse out of the cell and 6 water molecules and a bucket load of energy. Generally it produces 6 ATP molecules for every glucose molecule that goes in.

Now aerobic respiration can be used for other molecules besides glucose but we usually focus on glucose it's one of the primary fuel sources and then once you understand that you just say okay, we'll make some tiny modifications and see how we can plug in proteins and other molecules. Now like I said it produces 36 ATP but compared to anaerobic respiration without using oxygen it's slow and it does have that whole requirement about oxygen which is one of those annoying things I mean you hold your breath for a couple of minutes and you get kind of dizzy. Well, let's a look at how this happens the key organelle of aerobic respiration is the mitochondria.

Now the first step in the break down of glucose is glycolysis which happens in the cytosol or the cytoplasm of the cell. But once it's done then the molecules enter the mitochondria where it undergoes the series of chemical reactions that are called the Krebs cycle sometimes it's also called the tricarboxylic acid cycle or the citric acid cycle depending on which text book you use.

Finally it ends with a process known as the electron transport system. Let's take a closer look at how this happens, so here we see glucose which is a 6 carbon molecule that's what the little blue marbles here represent. And in going through the process known as glycolysis which means literally sugar splitting the glucose is split in half into a pair of 3 carbon molecules called pyruvate. This gives you some high energy electrons they were helping hold this together and those are sent off here to the electron transport system inside the mitochondria. You do get a little bit of ATP here but it's only 2 so not a big deal. The pyruvate eventually makes it's way into the inner portion of the mitochondria called the matrix where it undergoes the series of chemical reactions known as the Krebs cycle.

Again we get a little bit of energy molecules in the form of ATP or actually technically it's GTP and this is where we finally start releasing all of the carbon dioxides as they come flying out those carbons used to be in the glucose. We get a whole bunch more of these NADHs again they're high energy electron carriers and a couple of FADH 2 molecules. These are carrier molecules they literally carry electrons that have a lot of energy off to the molecules that make up something cleverly known as the electron transport system. The electron transport system uses the energy all of those high energy electrons to do something called proton pumping or hydrogen ion transport.

And what they do is they shove the hydrogen ions across the membrane then as those hydrogen ions make their way back across the membrane just like water going from one side of a dam through the other can drive a hydro dynamic electric generator. Here we see the high energy electrons have shoved the hydrogen ions across then as they go back they make bucket loads of ATP. Now we need some place to dump those high energy electrons and that's what oxygen is for. We dump the high energy electrons onto the O2 molecules they pick up a couple of hydrogen ions and become water. That's aerobic respiration.