WEBVTT 00:00:00.610 --> 00:00:03.360 Arguably, one of the most important molecules in all of 00:00:03.360 --> 00:00:06.150 biology is ATP. 00:00:06.150 --> 00:00:14.235 ATP, which stands for adenosine triphosphate. 00:00:18.690 --> 00:00:20.340 Which sounds very fancy. 00:00:20.340 --> 00:00:24.270 But all you need to remember, or any time you see ATP 00:00:24.270 --> 00:00:28.180 hanging around in some type of biochemical reaction, 00:00:28.180 --> 00:00:30.940 something in your brain should say, hey, we're dealing with 00:00:30.940 --> 00:00:32.360 biological energy. 00:00:32.360 --> 00:00:38.690 Or another way to think of ATP is the currency-- I'll put 00:00:38.690 --> 00:00:42.645 that in quotes-- of biological energy. 00:00:46.820 --> 00:00:49.000 So how is it a currency of energy? 00:00:49.000 --> 00:00:51.820 Well ATP stores energy in its bonds. 00:00:51.820 --> 00:00:54.040 And I'll explain what that means in a second. 00:00:54.040 --> 00:00:56.220 And before we learn what an adenosine group or a 00:00:56.220 --> 00:00:58.870 3-phosphate group looks like, you can just take a bit of a 00:00:58.870 --> 00:01:03.010 leap of faith, that you could imagine ATP as being made up 00:01:03.010 --> 00:01:06.160 of something called-- let me do it in a nice color-- an 00:01:06.160 --> 00:01:08.950 adenosine group right there. 00:01:08.950 --> 00:01:12.020 And then attached to it you'll have three phosphates. 00:01:12.020 --> 00:01:13.320 Not might, you will. 00:01:13.320 --> 00:01:18.150 You'll have three phosphates attached to it just like that. 00:01:18.150 --> 00:01:21.970 And this is ATP. 00:01:21.970 --> 00:01:24.450 Adenosine triphosphate. 00:01:24.450 --> 00:01:27.850 Tri- meaning three phosphate groups. 00:01:27.850 --> 00:01:31.235 Now if you take adenosine triphosphate and you hydrolyze 00:01:31.235 --> 00:01:33.460 this bond, which means if you take this in 00:01:33.460 --> 00:01:34.610 the presence of water. 00:01:34.610 --> 00:01:37.250 So let me just throw some water in here. 00:01:37.250 --> 00:01:41.610 Let's say I have H2O. 00:01:41.610 --> 00:01:44.450 Then one of these phosphate groups will break off. 00:01:44.450 --> 00:01:47.100 Essentially part of this water joins to this phosphate group, 00:01:47.100 --> 00:01:48.900 and then part of it joins to this 00:01:48.900 --> 00:01:49.900 phosphate group right there. 00:01:49.900 --> 00:01:51.590 And I'll show you that in a little bit more detail. 00:01:51.590 --> 00:01:53.960 But I want to give you the big picture first. 00:01:53.960 --> 00:01:57.430 What you're left with is an adenosine group that now has 00:01:57.430 --> 00:01:58.680 two phosphates on it. 00:02:01.460 --> 00:02:07.520 And this is called adenosine diphosphate or ADP. 00:02:07.520 --> 00:02:11.860 Before we had triphosphate, which means three phosphates. 00:02:11.860 --> 00:02:14.330 Now we have diphosphate, adenosine triphosphate, so 00:02:14.330 --> 00:02:16.650 instead of a tri here we just write a di. 00:02:16.650 --> 00:02:18.590 Which means you have two phosphate groups. 00:02:18.590 --> 00:02:22.760 And so the ATP has been hydrolyzed, or you have broken 00:02:22.760 --> 00:02:24.790 off one of these phosphate groups. 00:02:24.790 --> 00:02:27.550 And so now you're left with ADP and then an extra 00:02:27.550 --> 00:02:30.550 phosphate group right here. 00:02:30.550 --> 00:02:33.370 And-- and this is the whole key to everything that we talk 00:02:33.370 --> 00:02:35.660 about when we're dealing with ATP-- and 00:02:35.660 --> 00:02:36.910 you have some energy. 00:02:41.440 --> 00:02:45.590 And so when I talk about ATP being the currency of 00:02:45.590 --> 00:02:48.500 biological energy, this is why. 00:02:48.500 --> 00:02:52.220 Is that if you have ATP, and if you were to-- through some 00:02:52.220 --> 00:02:55.960 chemical reaction-- you pop off this phosphate right here. 00:02:55.960 --> 00:02:57.470 It's going to generate energy. 00:02:57.470 --> 00:02:59.960 That energy can be used for just general heat. 00:02:59.960 --> 00:03:02.810 Or you could couple this reaction with other reactions 00:03:02.810 --> 00:03:03.830 that require energy. 00:03:03.830 --> 00:03:07.960 And then those reactions will be able to move forward. 00:03:07.960 --> 00:03:10.490 So, I draw these circles. 00:03:10.490 --> 00:03:12.040 Adenosine and phosphates. 00:03:12.040 --> 00:03:15.010 And really, this is all you need to know. 00:03:15.010 --> 00:03:16.780 Already, what I've shown you right here is really all you 00:03:16.780 --> 00:03:20.660 need to know to operationally think of how ATP operates in 00:03:20.660 --> 00:03:22.390 most biological systems. And if you want to 00:03:22.390 --> 00:03:22.740 go the other way. 00:03:22.740 --> 00:03:25.020 If you have energy and you want to generate ATP, the 00:03:25.020 --> 00:03:26.050 reaction will just go this way. 00:03:26.050 --> 00:03:29.430 Energy plus a phosphate group plus some ADP, you 00:03:29.430 --> 00:03:30.610 can go back to ATP. 00:03:30.610 --> 00:03:32.940 And so this is stored energy. 00:03:32.940 --> 00:03:36.520 So this side of the equation is stored energy. 00:03:36.520 --> 00:03:39.220 And this side of the equation is used energy. 00:03:39.220 --> 00:03:43.810 And this is really all you--well this is 95% of what you 00:03:43.810 --> 00:03:46.430 need to know to really understand the function of ATP 00:03:46.430 --> 00:03:49.450 in biological systems. It's just a store of energy when 00:03:49.450 --> 00:03:51.150 you-- ATP has energy. 00:03:51.150 --> 00:03:54.070 When you break a phosphate off, it generates energy. 00:03:54.070 --> 00:03:56.700 And then if you want to go from ADP and a phosphate back 00:03:56.700 --> 00:03:59.580 to ATP, you have to use energy up again. 00:03:59.580 --> 00:04:02.040 So if you have ATP, that's a source of energy. 00:04:02.040 --> 00:04:06.580 If you have ADP and you want ATP, you need to use energy. 00:04:06.580 --> 00:04:09.500 And so far I've just drawn a circle with an A around it and 00:04:09.500 --> 00:04:10.460 said that's an adenosine. 00:04:10.460 --> 00:04:12.840 But sometimes I think it's satisfying to see what the 00:04:12.840 --> 00:04:14.180 molecule actually looks like. 00:04:14.180 --> 00:04:17.010 So I cut and pasted this from Wikipedia. 00:04:17.010 --> 00:04:19.310 And the reason why I didn't show this to you initially is 00:04:19.310 --> 00:04:20.829 because this looks very complicated. 00:04:20.829 --> 00:04:24.780 While the conceptual reason why ATP is the currency of 00:04:24.780 --> 00:04:26.710 energy, I think is fairly straightforward. 00:04:26.710 --> 00:04:30.200 When it has three phosphates, one phosphate can break off. 00:04:30.200 --> 00:04:33.310 And then that'll result with some energy being 00:04:33.310 --> 00:04:34.640 put into the system. 00:04:34.640 --> 00:04:36.560 Or if you want to attach that phosphate you 00:04:36.560 --> 00:04:37.560 have to use up energy. 00:04:37.560 --> 00:04:39.910 That's just the basic principle of ATP. 00:04:39.910 --> 00:04:44.010 But this is its actual structure. 00:04:44.010 --> 00:04:46.220 But even here we can break it down and see that it's really 00:04:46.220 --> 00:04:47.740 not too bad. 00:04:47.740 --> 00:04:48.790 We said adenosine. 00:04:48.790 --> 00:04:50.490 Let me draw the adenosine group. 00:04:50.490 --> 00:04:51.660 We have adenosine. 00:04:51.660 --> 00:04:54.220 This right here is adenosine. 00:04:54.220 --> 00:04:57.070 This part of the molecule right there. 00:04:57.070 --> 00:04:58.470 That is adenosine. 00:05:01.280 --> 00:05:04.340 And for those of you that have really paid attention to some 00:05:04.340 --> 00:05:07.560 of the other videos, you might recognize that this part of 00:05:07.560 --> 00:05:10.660 adenosine-- so this is called adenosine, but this part right 00:05:10.660 --> 00:05:12.820 here-- is adenine. 00:05:17.130 --> 00:05:21.110 Which is the same adenine that makes up the nucleotides that 00:05:21.110 --> 00:05:22.460 are the backbone of DNA. 00:05:22.460 --> 00:05:25.870 So some of these molecules in biological systems have more 00:05:25.870 --> 00:05:26.580 than one use. 00:05:26.580 --> 00:05:27.910 This is the same adenine where we talk 00:05:27.910 --> 00:05:30.170 about adenine and guanine. 00:05:30.170 --> 00:05:31.100 This is a purine. 00:05:31.100 --> 00:05:33.370 And there's also the pyrimidines, but I won't go 00:05:33.370 --> 00:05:33.920 into that much. 00:05:33.920 --> 00:05:35.180 But that's the same molecule. 00:05:35.180 --> 00:05:36.380 So that's just an interesting thing. 00:05:36.380 --> 00:05:39.950 The same thing that makes up DNA is also part of what makes 00:05:39.950 --> 00:05:42.940 up these energy currency molecules. 00:05:42.940 --> 00:05:47.700 So the adenine makes part of the adenosine part of ATP. 00:05:47.700 --> 00:05:50.210 And then the other part right here is ribose. 00:05:55.330 --> 00:06:00.970 Which you might also recognize from RNA, ribonucleic acid. 00:06:00.970 --> 00:06:03.040 That's because you have ribose dealing 00:06:03.040 --> 00:06:05.150 in the whole situation. 00:06:05.150 --> 00:06:06.190 But I won't go into that much. 00:06:06.190 --> 00:06:08.970 But ribose is just a 5-carbon sugar. 00:06:08.970 --> 00:06:11.340 When they don't draw the molecule, it's implied that 00:06:11.340 --> 00:06:11.950 it's a carbon. 00:06:11.950 --> 00:06:15.160 So this is one carbon right there, two carbons, three 00:06:15.160 --> 00:06:18.650 carbons, four carbons, five carbons. 00:06:18.650 --> 00:06:19.720 And that's just nice to know. 00:06:19.720 --> 00:06:21.840 It's nice to know that they share parts of their 00:06:21.840 --> 00:06:23.700 molecules with DNA. 00:06:23.700 --> 00:06:26.380 And these are familiar building blocks that we see 00:06:26.380 --> 00:06:27.260 over and over again. 00:06:27.260 --> 00:06:29.920 But I want to emphasize that knowing this, or memorizing 00:06:29.920 --> 00:06:32.270 this, in no way will help you understand the simpler 00:06:32.270 --> 00:06:35.360 understanding of ATP just being what 00:06:35.360 --> 00:06:37.520 drives biological reactions. 00:06:37.520 --> 00:06:41.520 And then here I drew 3-phosphate groups, and this 00:06:41.520 --> 00:06:43.350 is their actual molecular structure. 00:06:43.350 --> 00:06:44.490 Their Lewis structures right here. 00:06:44.490 --> 00:06:46.170 That's one phosphate group. 00:06:46.170 --> 00:06:48.530 This is the second phosphate group. 00:06:48.530 --> 00:06:52.320 And this is a third phosphate group. 00:06:52.320 --> 00:06:54.970 Just like that. 00:06:54.970 --> 00:06:58.830 When I first learned this, my first question was, OK I can 00:06:58.830 --> 00:07:02.080 take this as a leap of faith that if you take one of these 00:07:02.080 --> 00:07:05.590 phosphate groups off or if this bond is hydrolyzed, that 00:07:05.590 --> 00:07:07.020 somehow that releases energy. 00:07:07.020 --> 00:07:08.880 And then I kind of went on and answered all the questions 00:07:08.880 --> 00:07:09.570 that I had to answer. 00:07:09.570 --> 00:07:10.950 But why does it release energy? 00:07:10.950 --> 00:07:13.920 What is it about this bond that releases energy? 00:07:13.920 --> 00:07:16.690 Remember all bonds are are electrons being shared with 00:07:16.690 --> 00:07:17.830 different atoms. 00:07:17.830 --> 00:07:21.190 So the best way you could think about it is right here. 00:07:21.190 --> 00:07:24.900 These electrons that are being shared right across this bond, 00:07:24.900 --> 00:07:27.620 or this electron that's being shared right across this bond, 00:07:27.620 --> 00:07:29.470 and it's coming from the phosphate. 00:07:29.470 --> 00:07:31.680 I won't draw the Periodic Table right now. 00:07:31.680 --> 00:07:34.490 But you know the phosphate has five electrons to share. 00:07:34.490 --> 00:07:37.370 It's less electronegative than oxygen, so oxygen will kind of 00:07:37.370 --> 00:07:39.460 hog the electron. 00:07:39.460 --> 00:07:41.310 But this electron is very uncomfortable. 00:07:41.310 --> 00:07:43.930 There's a couple of reasons why it is uncomfortable. 00:07:43.930 --> 00:07:45.700 It's in a high energy state. 00:07:45.700 --> 00:07:47.250 One reason why is, you have all these 00:07:47.250 --> 00:07:48.720 negative oxygens here. 00:07:48.720 --> 00:07:50.590 So they kind of want to push away from each other. 00:07:50.590 --> 00:07:55.960 So these electrons in this bond really can't kind of get 00:07:55.960 --> 00:07:57.220 close to the nucleus. 00:07:57.220 --> 00:07:59.670 They'll go into kind of a low energy state. 00:07:59.670 --> 00:08:03.000 All of this is more of an analogy than the reality. 00:08:03.000 --> 00:08:05.210 We all know that electrons can get quite complex. 00:08:05.210 --> 00:08:07.430 And there's a whole quantum mechanical world. 00:08:07.430 --> 00:08:08.380 But that's a good way to think of it. 00:08:08.380 --> 00:08:10.840 That these molecules want to be away from each other. 00:08:10.840 --> 00:08:13.330 But you have these bonds, so this electron, it's kind of in 00:08:13.330 --> 00:08:14.395 a high energy state. 00:08:14.395 --> 00:08:17.250 It's further from the nucleuses of these two atoms 00:08:17.250 --> 00:08:18.580 than it might want to be. 00:08:18.580 --> 00:08:22.220 And when you pop this phosphate group off, all of a 00:08:22.220 --> 00:08:23.870 sudden these electrons can enter into a 00:08:23.870 --> 00:08:25.110 lower energy state. 00:08:25.110 --> 00:08:27.080 And that generates energy. 00:08:27.080 --> 00:08:32.030 So this energy right here is always-- in fact in any 00:08:32.030 --> 00:08:34.409 chemical reaction where they say energy is generated, it's 00:08:34.409 --> 00:08:37.200 always from electrons going to a lower energy state. 00:08:47.510 --> 00:08:48.570 That's what it's all about. 00:08:48.570 --> 00:08:50.610 And later in future videos when we do cellular 00:08:50.610 --> 00:08:54.480 respiration and glycolysis and all that, whenever we show 00:08:54.480 --> 00:08:57.330 energy, it's really from electrons going from 00:08:57.330 --> 00:08:59.900 uncomfortable states to more comfortable states. 00:08:59.900 --> 00:09:02.640 And in the process they generate energy. 00:09:02.640 --> 00:09:05.620 If I'm in a plane or I'm jumping out of a plane, I have 00:09:05.620 --> 00:09:07.180 a lot of potential energy right when I 00:09:07.180 --> 00:09:08.050 jump out of the plane. 00:09:08.050 --> 00:09:10.280 And you can view that as an uncomfortable state. 00:09:10.280 --> 00:09:13.350 And then when I'm sitting on my couch watching football, I 00:09:13.350 --> 00:09:15.690 have a lot less potential energy, so that's a very 00:09:15.690 --> 00:09:16.500 comfortable state. 00:09:16.500 --> 00:09:18.790 And I could have generated a lot of energy 00:09:18.790 --> 00:09:20.480 falling to my couch. 00:09:20.480 --> 00:09:21.590 But I don't knows. 00:09:21.590 --> 00:09:24.540 My analogies always break down at some point. 00:09:24.540 --> 00:09:28.230 Now, the last thing I want to go over for you is exactly how 00:09:28.230 --> 00:09:29.530 this reaction happens. 00:09:29.530 --> 00:09:32.410 So far you could turn off this video and you could already 00:09:32.410 --> 00:09:35.680 deal with ATP as it is used in 95% of biology, 00:09:35.680 --> 00:09:36.790 especially AP Bio. 00:09:36.790 --> 00:09:38.630 But I want you to understand how this 00:09:38.630 --> 00:09:40.320 reaction actually happens. 00:09:40.320 --> 00:09:43.110 So to do that, what I'm going to do is copy and 00:09:43.110 --> 00:09:44.150 paste parts of these. 00:09:44.150 --> 00:09:46.170 So I already told you that this guy right here is going 00:09:46.170 --> 00:09:51.280 to break off of the ATP. 00:09:58.490 --> 00:10:01.030 So that's the phosphate group that breaks off. 00:10:01.030 --> 00:10:02.360 And then you have the rest of it. 00:10:02.360 --> 00:10:05.310 You have the ADP that's left over. 00:10:05.310 --> 00:10:07.530 So this is the ADP. 00:10:07.530 --> 00:10:09.340 I don't even have to copy and paste all of this stuff. 00:10:09.340 --> 00:10:12.000 You can just accept that that's the adenosine group. 00:10:18.050 --> 00:10:19.500 Just like that. 00:10:19.500 --> 00:10:22.240 So we've already said that this thing gets hydrolyzed 00:10:22.240 --> 00:10:24.930 off, or gets cut off and that generates energy. 00:10:24.930 --> 00:10:25.770 But what I want to do is actually 00:10:25.770 --> 00:10:28.300 show you the mechanism. 00:10:28.300 --> 00:10:30.260 A little bit of hand-wavy mechanism of how 00:10:30.260 --> 00:10:31.630 this actually happens. 00:10:31.630 --> 00:10:34.825 So I said this reaction occurs in the presence of water. 00:10:34.825 --> 00:10:37.210 So let me draw some water here. 00:10:37.210 --> 00:10:40.040 So I have an oxygen and a hydrogen. 00:10:40.040 --> 00:10:42.100 And then I have another hydrogen. 00:10:42.100 --> 00:10:43.710 That's water right there. 00:10:43.710 --> 00:10:47.360 So hydrolysis is just a reaction where you say, hey, 00:10:47.360 --> 00:10:51.420 this guy here, he wants to bond with something or he 00:10:51.420 --> 00:10:53.920 wants to share someone else's electrons. 00:10:53.920 --> 00:10:58.500 So maybe this hydrogen right here goes down here and shares 00:10:58.500 --> 00:11:02.250 its electron with this oxygen right here. 00:11:02.250 --> 00:11:06.320 And then this phosphorus, it has an extra electron that it 00:11:06.320 --> 00:11:06.820 needs to share. 00:11:06.820 --> 00:11:09.190 Remember it has five valence electrons; it wants to share 00:11:09.190 --> 00:11:10.360 them with oxygen. 00:11:10.360 --> 00:11:14.040 It has one, two, three, four being shared right now. 00:11:14.040 --> 00:11:17.670 Well, if this hydrogen goes to this guy, then you're left 00:11:17.670 --> 00:11:19.980 with this blue OH right here. 00:11:19.980 --> 00:11:22.460 And this guy can share one of the 00:11:22.460 --> 00:11:24.810 phosphorus' extra electrons. 00:11:24.810 --> 00:11:27.190 So you get the OH just like that. 00:11:27.190 --> 00:11:29.230 So that's the actual process that happens. 00:11:29.230 --> 00:11:31.350 And it could go the other way as well. 00:11:31.350 --> 00:11:33.040 I could've cleaved it here. 00:11:33.040 --> 00:11:34.740 I could have cleaved the whole thing here. 00:11:34.740 --> 00:11:37.270 And so this guy would have kept the oxygen and the 00:11:37.270 --> 00:11:38.890 hydrogen would have gone to him. 00:11:38.890 --> 00:11:40.820 And then this guy would have taken the OH. 00:11:40.820 --> 00:11:42.540 It could happen in either order. 00:11:42.540 --> 00:11:44.765 And so either order would be fine. 00:11:44.765 --> 00:11:47.010 And there's one other point I want to make. 00:11:47.010 --> 00:11:48.435 And this is a little bit more complex. 00:11:48.435 --> 00:11:50.930 And I was even wondering whether I wanted to make it. 00:11:50.930 --> 00:11:53.310 My whole reason why you're kind of in a lower energy 00:11:53.310 --> 00:11:56.510 state is, once you break apart--actually let me go 00:11:56.510 --> 00:12:00.370 down here-- is because I said, hey, this electron is happier 00:12:00.370 --> 00:12:03.090 when it's-- so let's say this electron that was part of this 00:12:03.090 --> 00:12:04.760 phosphorus is happier now. 00:12:04.760 --> 00:12:06.540 It's in a lower energy state because 00:12:06.540 --> 00:12:07.950 it's not being stretched. 00:12:07.950 --> 00:12:10.350 It's not having to spend time between that guy and that guy 00:12:10.350 --> 00:12:13.050 because this molecule and this molecule want to spread apart 00:12:13.050 --> 00:12:14.560 because they have negative charges. 00:12:14.560 --> 00:12:15.910 That's part of the reason. 00:12:15.910 --> 00:12:18.410 The other reason why, and we'll talk about this in a lot 00:12:18.410 --> 00:12:21.540 more detail when we learn more about organic chemistry, is 00:12:21.540 --> 00:12:23.940 that this has more resonance. 00:12:23.940 --> 00:12:27.770 More resonance structures or resonance configurations. 00:12:27.770 --> 00:12:31.360 And all that means is that these electrons, these extra 00:12:31.360 --> 00:12:34.240 electrons here, they can kind of move about between the 00:12:34.240 --> 00:12:37.170 different atoms. And that makes it even more stable. 00:12:37.170 --> 00:12:40.910 So if you imagine that this oxygen right here has an extra 00:12:40.910 --> 00:12:42.700 electron with it. 00:12:42.700 --> 00:12:47.840 So that extra electron right there, it could come down here 00:12:47.840 --> 00:12:51.180 and then form a double bond with the phosphorus. 00:12:51.180 --> 00:12:54.810 And then this electron right here can then jump back up to 00:12:54.810 --> 00:12:55.870 that oxygen. 00:12:55.870 --> 00:12:58.400 And then that could happen on this side and on that side. 00:12:58.400 --> 00:12:59.990 And I won't go into the details, but that's another 00:12:59.990 --> 00:13:01.800 reason why it makes it more stable. 00:13:01.800 --> 00:13:03.590 If you've already taken organic chemistry, you can 00:13:03.590 --> 00:13:05.080 kind of appreciate that more. 00:13:05.080 --> 00:13:07.570 But I don't want to get all into the weeds. 00:13:07.570 --> 00:13:11.120 The most important thing to remember about ATP is that 00:13:11.120 --> 00:13:14.460 when you cleave off a phosphate group it generates 00:13:14.460 --> 00:13:17.950 energy that can drive all sorts of biological functions, 00:13:17.950 --> 00:13:20.570 like growth and movement, muscle movement, muscle 00:13:20.570 --> 00:13:23.900 contraction, electrical impulses in 00:13:23.900 --> 00:13:25.290 nerves and the brain. 00:13:25.290 --> 00:13:29.310 So this is the main battery or currency of energy in 00:13:29.310 --> 00:13:32.540 biological systems. That's the main thing that you really 00:13:32.540 --> 00:13:33.790 just need to remember about ATP.