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Biology: ATP Structure and Function


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About this Lesson

  • Type: Video Tutorial
  • Length: 11:09
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 120 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Respiration (17 lessons, $28.71)
Biology: An Introduction to Respiration (6 lessons, $10.89)

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 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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How does a cell do work? How does this bag of chemical do work? Now, to me, work is things like picking up heavy metal objects and lifting them over your head, and moving plastic things around - and that's work. How does a cell do work? Well, you know, if we could figure out how a cell does work, well, then, we have the true secret to life, because without the ability to do work, you don't have any sort of life form. Work, even at the level of a bacteria, means that energy has to be given off, which brings us to ATP - the moment you've all been waiting for - ATP.
What is ATP, and how does it have anything to do with cell work? Well, ATP is written like that. It stands for "adenosine triphosphate." Once again, if you understand, the doors are open to you. Well, maybe you don't know what adenosine is, but you sure know that triphosphate must mean that there are three phosphate groups. You know that phosphate groups - that functional side group - is a phosphorous surrounded by oxygens. You know that phosphate groups are involved in phosphorylated intermediates for energy transfer. So ATP must have three phosphates attached.
Let's take a look at ATP and see if it looks vaguely familiar. This is kind of interesting; what do we have here? If you take a look at this, we see what looks to be like some kind of monosaccharide. And we see what seems to be a two-ringed nitrogen-containing compound. And we see what looks like phosphate groups up here. Wow, does this look familiar? To me, I seem to remember learning once the idea of something called a nucleotide. And a nucleotide had nothing to do with energy use; a nucleotide was the building block of DNA. And a nucleotide looks something like this: a house with a driveway, which was the nitrogenous base with a swimming pool attached. A house with - well, that's the house, that's the driveway - with, oh, three swimming pools attached. Well, there you go - there's the big difference between this and the nucleotide that goes into DNA. Although this does indeed contain A, this is triphosphorylated. In essence, ATP is a triphosphorylated nucleotide. How cool is that? It is a trinucleotide - a triphosphated nucleotide - a triphosphate nucleotide. Why am I putting these big old exclamation marks over there? This is very exciting. This points out something that I really want you guys to understand: Life uses things in many different ways, and just because you had it cemented into your head that A was part of DNA doesn't mean it can't be part of something else. So it's very important to see that even the constituents of different molecules can be the same, and shape and arrangement is what it's all about.
What I want to talk to you about is how ATP ends up as this so-called molecule of energy. Well, here's, once again, our comparison. This is what our DNA nucleotide looks like; this is what ATP looks like. Now, I'm going to put this aside because I want to simplify this. ATP is often written like so: A P - sometimes with a P there - no, always with a P there - and always with this - occasionally, they'll put this little curvy bond over here. Let's not worry too much about that; let's worry about did I draw this incorrectly, and the answer is no. We refer to this as a high-energy bond. And what that simply means is this: that ATP has energy supposedly in the bond between its 2 P's. But I have to tell you, I'm a little bit nervous about calling that a high-energy bond, because it's kind of a misnomer. To call that a high-energy bond suggests that there are such things as low-energy bonds. But I've got to tell you, to break a bond takes an enormous input of energy, I don't care what kind of bond you have. See, if bonds weren't stable, they wouldn't be there to begin with. So bonds tend to be very stable.
So then why do we call this a high-energy bond? Any bond takes energy to break it. So, if that's true, what is up with this, and how is ATP going to be working? Well, you know, maybe, that when ATP releases its energy, it goes through a process - enzymatically driven - where it yields a diphosphate molecule called ADP, and it breaks off a phosphate group. Here comes the energy, guys. It's in the breaking of this bond that energy is released - that's the key. It's the whole free energy story that I want to review for you, that that's the key to the energy of ATP.
Let's take a close look at this. ATP - once again, let's take a look at this triphosphorylated nucleotide - has a negative charge - look at all the negatives on this: 1, 2, 3, 4; there are a 4 negatives on that thing. When you break that ATP, here's what's going to happen: I want you to look at the charge, because this is going to be the key. ATP has a charge, therefore, of -4. When we break that bond, therefore - we're going to hydrolyze it, we're going to add water to it - remember hydrolysis, adding water - we are going to end up with ADP. And that ADP has lost the phosphate group, and it's going to be -3 now, and it's going to form a phosphate group - hydrogen is going to be picked up there - HPO[4], and that's going to be -2.
Well, what just happened - don't worry about the fact that the numbers aren't adding up; that's okay, because we have the water thrown in here. Here's the thing, and this is what I want you to understand: that it is the fact that these things are so highly charged that releases the energy. You see, the point of the matter is, is that this thing right here, with its high charges, is being held in place - this whole TP thing - is being held in place, and those negatives - there are a lot of repulsive forces with all these light charges in there. And as soon as you enzymatically allow that to occur through a hydrolytic reaction, it is very unlikely that these things are going to go back together. Let's look at the delta G story on this thing. Remember delta G? I know you know about delta G. Delta G - the laws of basic dynamics, the change in free energy, is equal to the way - the way I have said it to you is like this: The final amount of free energy minus the initial amount of free energy.
Now let's review that and see what happens here. That means that, if you had - these are your products, that's your final products, and these are your reactants, the things that you're doing, or breaking, or whatever. In this case, my reactant is ATP; my products are A, D, P, and P. Well, let's think about it. My reactants - my ATP - has a high amount of energy. My ADP, and my phosphate group, has a lower. Well, when I take a lower number and I subtract a higher number from it, what am I going to get? A negative number. And remember free energy: When that number is negative, that means it's been a catabolic and exergonic reaction; and, therefore, you have given off energy. And we compute these things in calorimeters, and ATP's energy releases fairly high. When you break that bond, it gives off -7.3 kilocalories per mole of ATP. The only thing that makes that important is, when you compare that to other exergonic reactions, -7.3 is high; that's a lot of energy being given off. So one reason ATP is a high-energy bond is because of the unlikelihood of that thing going back in the other direction spontaneously. In other words, energy is released, and nothing's going to go back together.
There's another reason, too, and it has to do with a very complex chemical situation that I want to tell you about called resonance hybrids. Those of you who know chemistry are running out of the room now. Come back! I'm not going to say too much about these. Resonance hybrids are simply this: When you get a molecule that forms, the electrons will tend to fall back to their most stable position, and it is the fact that this happens that these resonance hybrids form. And this rearrangement is that the ADP and the P become more stable. The fact that they're more stable tells you something: Energy has been released. When electrons are way out here, they're high energy, and when they're closer in, they're lower energy. The fact that they have formed a resonance hybrid means that energy has been released.
So here we have it: ATP - high-energy bonds. Is it the bond that's high energy? No, that bond isn't high energy, but what happens when that bond is broken releases the energy. And now I have a question for you: Where does the energy go? I'm not going to tell you right now; you're going to have to find out later.
An Introduction to Respiration
ATP Structure and Function Page [1 of 2]

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