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Biology: Aerobic Respiration: The Acetyl CoA Step

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About this Lesson

  • Type: Video Tutorial
  • Length: 9:26
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 101 MB
  • Posted: 07/02/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Respiration (17 lessons, $28.71)
Biology: Aerobic Respiration, Glycolysis & Krebs (3 lessons, $5.94)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at http://www.thinkwell.com/student/product/biology. The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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Loved this video
08/07/2012
~ Tina11

I keep watching it over and over. This guy is great, he keeps my attention, which is not easy to do!

4_homepage
Loved this video
08/07/2012
~ Tina11

I keep watching it over and over. This guy is great, he keeps my attention, which is not easy to do!

So now that you have all this pyruvate, what are you going to do with it? What are you going to do with all that pyruvate? And now you made all this NAD, and you made this ATP. Well, I want to know what you're going to do with the pyruvate. See, you're a eukaryote, and you have a mitochondrion. So now, we can take this pyruvate and we can do some great things with it. Let's just take a general overview, where we've been, and where you and I as eukaryotes are going to go with it.
Well, remember that we started out with glucose. And there's a very important concept I want you to get right here, and it's this: That this is an overview of what's going on in the cell, and there's something I don't want you to forget. The first step of this whole idea of this respiratory pathway happens in the cytosol. It's not in the mitochondria yet. That's going to loom fairly big later on. So we know that right here we have managed to generate a molecule of pyruvate. So now we have pyruvate, and you know what happens if you lack a mitochondria. If you lack a mitochondria, you have to go along this route, and that is the fermentative route, and you might, for example, make ethanol, or you might make lactic acid, or lactate; there's a lot of different things you can do. So we'll just put ethanol and lactic acid as examples of things that might happen - not in your cells. I know, for those of you who are college students, you're probably saying to yourself, "Wouldn't it be great if I could make ethanol in my own cells?" I hope you're not saying that; I hope you're studious individuals who don't think of ethanol as a recreational activity, consumption of ethanol. But in case you do or ever do, this thing right here is not possible in our cells, which is good, because you'd be running around drunk all the time.
Instead, what we do, is we move it into the mitochondria, and in the mitochondria, we are going to generate some other things. In the mitochondria we are going to generate a substance called acetyl - well, we're going to generate, we're going to actually break this thing apart, and we're going to go through aerobic respiration.
Now, before we enter the mitochondria, we have to make a substance called acetyl CoA. That is going to be the entrance key into this whole respiratory pathway. But, eventually, we are going to generate from this pyruvate carbon dioxide and water. Look at the difference. Here, we end up with some major organics - ethanol or lactic acid - here, we further take that glucose, rip it apart, and end up with CO[2] and water. That's the magic we're going to talk about right now - how do we do this.
The entrance key to the respiratory pathway is a substance called acetyl CoA. If you don't have acetyl CoA, you're not going anywhere in the mitochondria. And that's what I want to show you, I want to show you how we make the substance called acetyl CoA. Now don't forget the whole doubling system here. Remember we have C[6]H[12]O[6] that was broken down into 2 three-carbon pyruvates, so all the time, as we go through some of these systems, and we go through some of the metabolic pathways, you'll often see pyruvate by itself. But don't forget, unless I tell you - and I'll try to remind you all the time - pyruvate is going to be double, because we have 2 pyruvates, because when all is said and done, we're trying to find out the yield of a glucose molecule, which is C[6]. But, again, the process is as important as anything else. Understand what's going to go on here and you're going to be in great shape.
Let's take a look at pyruvate. Pyruvate - what do we want to do with this pyruvate? Well, the first thing we want to do is we want to get it ready to go into a series of reactions that are going to take those electrons, move those electrons from high-energy level to low-energy level, and use those electrons as much as we can. Now remember - I keep going back to glycolysis - glycolysis is an important step in the sense that we did that a lot, and bacteria are perfectly happy now, because they have made their ATP. But the question I have for you is: Are there more bonds here? And if there are more bonds there, might we be able to squeak out a little more energy? Might we be able to rip off a few more hydrogens? Might we be able to reduce a few more coenzymes and maybe make a little more ATP? That's the challenge of evolution. Let's see if we can.
Well, the way we're going to do that is - step one, the first step in the, what we're going to call the acetyl CoA step. The acetyl CoA step is going to be a process called decarboxylation. You've heard of that before. Decarboxylation: a removal of a CO[2] molecule. Now you all know, you learned this back in second grade, that we breathe out carbon dioxide. Well, where does that carbon dioxide come from? Guess what? That's one of the places that carbon dioxide comes from. In the acetyl CoA step, we are actually going to remove carbon dioxide. So we're going to remove a CO[2] from this group. So isn't that great, we're going to remove CO[2].
So carbon dioxide is going to be a waste product. Well, that's obviously going to give us a two-carbon substance - kind of cool. Now, you're probably saying, "Well, wait a minute. If that's the final product, and we removed 2 oxygens, there should only be 1 oxygen left." Well, that's going to kind of work here, isn't it? I don't want to tip my hat there, but I felt you thinking that. So this, by the way, is acetyl CoA - make believe you never saw that.
Here's the next thing. More good news for you energy fans - what we're going to do is we're going to take this NAD, we're going to take more NAD, still more NAD, and reduce it to more NADH+H. And so we have another reduction happening. Think of that. Do you remember what that means? By now you've heard it so many times it's like ingrained into your head, but it's a transfer of electrons. And in reducing this NAD+ to NADH+H, once again, remember what's happening here. What's happening is an energy conversion. We now have an NADH+H that has in essence ripped hydrogens again from glucose. Remember pyruvate came from glucose. So we once again have come up with a way to use glucose to reduce a coenzyme, therefore moving the energy from glucose into the coenzyme. Have you figured out that, man, these coenzymes are going to be major, big-time things when it comes to eventually getting this energy into ATP?
So here we go, we just made another reduction. And now what's going to happen is we are going to add while we're doing this CoA. Believe me on that one, because when we're done, we are going to have a substance called acetyl CoA. CoA, by the way, coenzyme-A, is another one of those B-vitamin derivates. So now, as soon as we attached this CoA in here, this acetyl group - remember your chemistry, a two-carbon group - this acetyl group is going to be very unstable. Remember unstability? Remember what that means? That means that this is something that is very prone to reaction, and therefore prone to release energy.
So we have in essence come up with the key to the next series of steps, and what is that going to be? Taking the energy - and remember, these 2 red carbons were once part of glucose - all we have now - we've lost some carbon, we've lost like 1/3 of our carbon from that original glucose, because remember, there are 2 of these pyruvates; therefore, there's going to be 2 of these CO[2]'s and there are going to be 2 of these acetyl CoA's - we're all okay with that. But the bottom line is this: What we now have is a fairly high-energy compound, a fairly unstable compound; and that unstable compound, in essence, is a destabilized pyruvate. Go back - pyruvate, 2 three-carbon substances that 10 minutes ago you thought, "Hey, we took a lot of energy out of there; we doubled our energy." Now, all of a sudden, I've given you the key to get into that mitochondria and take more energy out of that glucose. Wait till you see how much.
Respiration
Aerobic Respiration
Aerobic Respiration: The Acetyl CoA Step Page [1 of 2]

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