0:00:00.610,0:00:03.360 Arguably, one of the most important molecules in all of 0:00:03.360,0:00:06.150 biology is ATP. 0:00:06.150,0:00:14.235 ATP, which stands for adenosine triphosphate. 0:00:18.690,0:00:20.340 Which sounds very fancy. 0:00:20.340,0:00:24.270 But all you need to remember, or any time you see ATP 0:00:24.270,0:00:28.180 hanging around in some type of biochemical reaction, 0:00:28.180,0:00:30.940 something in your brain should say, hey, we're dealing with 0:00:30.940,0:00:32.360 biological energy. 0:00:32.360,0:00:38.690 Or another way to think of ATP is the currency-- I'll put 0:00:38.690,0:00:42.645 that in quotes-- of biological energy. 0:00:46.820,0:00:49.000 So how is it a currency of energy? 0:00:49.000,0:00:51.820 Well ATP stores energy in its bonds. 0:00:51.820,0:00:54.040 And I'll explain what that[br]means in a second. 0:00:54.040,0:00:56.220 And before we learn what an adenosine group or a 0:00:56.220,0:00:58.870 3-phosphate group looks like, you can just take a bit of a 0:00:58.870,0:01:03.010 leap of faith, that you could imagine ATP as being made up 0:01:03.010,0:01:06.160 of something called-- let me do it in a nice color-- an 0:01:06.160,0:01:08.950 adenosine group right there. 0:01:08.950,0:01:12.020 And then attached to it you'll have three phosphates. 0:01:12.020,0:01:13.320 Not might, you will. 0:01:13.320,0:01:18.150 You'll have three phosphates attached to it just like that. 0:01:18.150,0:01:21.970 And this is ATP. 0:01:21.970,0:01:24.450 Adenosine triphosphate. 0:01:24.450,0:01:27.850 Tri- meaning three phosphate groups. 0:01:27.850,0:01:31.235 Now if you take adenosine triphosphate and you hydrolyze 0:01:31.235,0:01:33.460 this bond, which means if you take this in 0:01:33.460,0:01:34.610 the presence of water. 0:01:34.610,0:01:37.250 So let me just throw some water in here. 0:01:37.250,0:01:41.610 Let's say I have H2O. 0:01:41.610,0:01:44.450 Then one of these phosphate groups will break off. 0:01:44.450,0:01:47.100 Essentially part of this water joins to this phosphate group, 0:01:47.100,0:01:48.900 and then part of it joins to this 0:01:48.900,0:01:49.900 phosphate group right there. 0:01:49.900,0:01:51.590 And I'll show you that in a little bit more detail. 0:01:51.590,0:01:53.960 But I want to give you the big picture first. 0:01:53.960,0:01:57.430 What you're left with is an adenosine group that now has 0:01:57.430,0:01:58.680 two phosphates on it. 0:02:01.460,0:02:07.520 And this is called adenosine diphosphate or ADP. 0:02:07.520,0:02:11.860 Before we had triphosphate, which means three phosphates. 0:02:11.860,0:02:14.330 Now we have diphosphate, adenosine triphosphate, so 0:02:14.330,0:02:16.650 instead of a tri here we just write a di. 0:02:16.650,0:02:18.590 Which means you have two phosphate groups. 0:02:18.590,0:02:22.760 And so the ATP has been hydrolyzed, or you have broken 0:02:22.760,0:02:24.790 off one of these phosphate groups. 0:02:24.790,0:02:27.550 And so now you're left with ADP and then an extra 0:02:27.550,0:02:30.550 phosphate group right here. 0:02:30.550,0:02:33.370 And-- and this is the whole key to everything that we talk 0:02:33.370,0:02:35.660 about when we're dealing with ATP-- and 0:02:35.660,0:02:36.910 you have some energy. 0:02:41.440,0:02:45.590 And so when I talk about ATP being the currency of 0:02:45.590,0:02:48.500 biological energy, this is why. 0:02:48.500,0:02:52.220 Is that if you have ATP, and if you were to-- through some 0:02:52.220,0:02:55.960 chemical reaction-- you pop off this phosphate right here. 0:02:55.960,0:02:57.470 It's going to generate energy. 0:02:57.470,0:02:59.960 That energy can be used for just general heat. 0:02:59.960,0:03:02.810 Or you could couple this reaction with other reactions 0:03:02.810,0:03:03.830 that require energy. 0:03:03.830,0:03:07.960 And then those reactions will be able to move forward. 0:03:07.960,0:03:10.490 So, I draw these circles. 0:03:10.490,0:03:12.040 Adenosine and phosphates. 0:03:12.040,0:03:15.010 And really, this is all you need to know. 0:03:15.010,0:03:16.780 Already, what I've shown you[br]right here is really all you 0:03:16.780,0:03:20.660 need to know to operationally think of how ATP operates in 0:03:20.660,0:03:22.390 most biological systems. And if you want to 0:03:22.390,0:03:22.740 go the other way. 0:03:22.740,0:03:25.020 If you have energy and you want to generate ATP, the 0:03:25.020,0:03:26.050 reaction will just go this way. 0:03:26.050,0:03:29.430 Energy plus a phosphate group plus some ADP, you 0:03:29.430,0:03:30.610 can go back to ATP. 0:03:30.610,0:03:32.940 And so this is stored energy. 0:03:32.940,0:03:36.520 So this side of the equation is stored energy. 0:03:36.520,0:03:39.220 And this side of the equation is used energy. 0:03:39.220,0:03:43.810 And this is really all you--well this is 95% of what you 0:03:43.810,0:03:46.430 need to know to really understand the function of ATP 0:03:46.430,0:03:49.450 in biological systems. It's just a store of energy when 0:03:49.450,0:03:51.150 you-- ATP has energy. 0:03:51.150,0:03:54.070 When you break a phosphate off, it generates energy. 0:03:54.070,0:03:56.700 And then if you want to go from ADP and a phosphate back 0:03:56.700,0:03:59.580 to ATP, you have to use[br]energy up again. 0:03:59.580,0:04:02.040 So if you have ATP, that's a source of energy. 0:04:02.040,0:04:06.580 If you have ADP and you want ATP, you need to use energy. 0:04:06.580,0:04:09.500 And so far I've just drawn a circle with an A around it and 0:04:09.500,0:04:10.460 said that's an adenosine. 0:04:10.460,0:04:12.840 But sometimes I think it's satisfying to see what the 0:04:12.840,0:04:14.180 molecule actually looks like. 0:04:14.180,0:04:17.010 So I cut and pasted this from Wikipedia. 0:04:17.010,0:04:19.310 And the reason why I didn't show this to you initially is 0:04:19.310,0:04:20.829 because this looks very complicated. 0:04:20.829,0:04:24.780 While the conceptual reason why ATP is the currency of 0:04:24.780,0:04:26.710 energy, I think is fairly straightforward. 0:04:26.710,0:04:30.200 When it has three phosphates, one phosphate can break off. 0:04:30.200,0:04:33.310 And then that'll result with some energy being 0:04:33.310,0:04:34.640 put into the system. 0:04:34.640,0:04:36.560 Or if you want to attach that phosphate you 0:04:36.560,0:04:37.560 have to use up energy. 0:04:37.560,0:04:39.910 That's just the basic principle of ATP. 0:04:39.910,0:04:44.010 But this is its actual structure. 0:04:44.010,0:04:46.220 But even here we can break it down and see that it's really 0:04:46.220,0:04:47.740 not too bad. 0:04:47.740,0:04:48.790 We said adenosine. 0:04:48.790,0:04:50.490 Let me draw the adenosine group. 0:04:50.490,0:04:51.660 We have adenosine. 0:04:51.660,0:04:54.220 This right here is adenosine. 0:04:54.220,0:04:57.070 This part of the molecule[br]right there. 0:04:57.070,0:04:58.470 That is adenosine. 0:05:01.280,0:05:04.340 And for those of you that have really paid attention to some 0:05:04.340,0:05:07.560 of the other videos, you might[br]recognize that this part of 0:05:07.560,0:05:10.660 adenosine-- so this is called adenosine, but this part right 0:05:10.660,0:05:12.820 here-- is adenine. 0:05:17.130,0:05:21.110 Which is the same adenine that makes up the nucleotides that 0:05:21.110,0:05:22.460 are the backbone of DNA. 0:05:22.460,0:05:25.870 So some of these molecules in biological systems have more 0:05:25.870,0:05:26.580 than one use. 0:05:26.580,0:05:27.910 This is the same adenine where we talk 0:05:27.910,0:05:30.170 about adenine and guanine. 0:05:30.170,0:05:31.100 This is a purine. 0:05:31.100,0:05:33.370 And there's also the[br]pyrimidines, but I won't go 0:05:33.370,0:05:33.920 into that much. 0:05:33.920,0:05:35.180 But that's the same molecule. 0:05:35.180,0:05:36.380 So that's just an interesting thing. 0:05:36.380,0:05:39.950 The same thing that makes up DNA[br]is also part of what makes 0:05:39.950,0:05:42.940 up these energy currency molecules. 0:05:42.940,0:05:47.700 So the adenine makes part of the adenosine part of ATP. 0:05:47.700,0:05:50.210 And then the other part[br]right here is ribose. 0:05:55.330,0:06:00.970 Which you might also recognize from RNA, ribonucleic acid. 0:06:00.970,0:06:03.040 That's because you have ribose dealing 0:06:03.040,0:06:05.150 in the whole situation. 0:06:05.150,0:06:06.190 But I won't go into that much. 0:06:06.190,0:06:08.970 But ribose is just a 5-carbon sugar. 0:06:08.970,0:06:11.340 When they don't draw the molecule, it's implied that 0:06:11.340,0:06:11.950 it's a carbon. 0:06:11.950,0:06:15.160 So this is one carbon right there, two carbons, three 0:06:15.160,0:06:18.650 carbons, four carbons, five carbons. 0:06:18.650,0:06:19.720 And that's just nice to know. 0:06:19.720,0:06:21.840 It's nice to know that they share parts of their 0:06:21.840,0:06:23.700 molecules with DNA. 0:06:23.700,0:06:26.380 And these are familiar building blocks that we see 0:06:26.380,0:06:27.260 over and over again. 0:06:27.260,0:06:29.920 But I want to emphasize that knowing this, or memorizing 0:06:29.920,0:06:32.270 this, in no way will help you understand the simpler 0:06:32.270,0:06:35.360 understanding of ATP just being what 0:06:35.360,0:06:37.520 drives biological reactions. 0:06:37.520,0:06:41.520 And then here I drew 3-phosphate groups, and this 0:06:41.520,0:06:43.350 is their actual molecular structure. 0:06:43.350,0:06:44.490 Their Lewis structures right here. 0:06:44.490,0:06:46.170 That's one phosphate group. 0:06:46.170,0:06:48.530 This is the second phosphate group. 0:06:48.530,0:06:52.320 And this is a third phosphate group. 0:06:52.320,0:06:54.970 Just like that. 0:06:54.970,0:06:58.830 When I first learned this, my first question was, OK I can 0:06:58.830,0:07:02.080 take this as a leap of faith that if you take one of these 0:07:02.080,0:07:05.590 phosphate groups off or if this bond is hydrolyzed, that 0:07:05.590,0:07:07.020 somehow that releases energy. 0:07:07.020,0:07:08.880 And then I kind of went on and answered all the questions 0:07:08.880,0:07:09.570 that I had to answer. 0:07:09.570,0:07:10.950 But why does it release energy? 0:07:10.950,0:07:13.920 What is it about this bond that releases energy? 0:07:13.920,0:07:16.690 Remember all bonds are are electrons being shared with 0:07:16.690,0:07:17.830 different atoms. 0:07:17.830,0:07:21.190 So the best way you could think about it is right here. 0:07:21.190,0:07:24.900 These electrons that are being shared right across this bond, 0:07:24.900,0:07:27.620 or this electron that's being shared right across this bond, 0:07:27.620,0:07:29.470 and it's coming from the phosphate. 0:07:29.470,0:07:31.680 I won't draw the Periodic Table right now. 0:07:31.680,0:07:34.490 But you know the phosphate has five electrons to share. 0:07:34.490,0:07:37.370 It's less electronegative than oxygen, so oxygen will kind of 0:07:37.370,0:07:39.460 hog the electron. 0:07:39.460,0:07:41.310 But this electron is very uncomfortable. 0:07:41.310,0:07:43.930 There's a couple of reasons why it is uncomfortable. 0:07:43.930,0:07:45.700 It's in a high energy state. 0:07:45.700,0:07:47.250 One reason why is, you have all these 0:07:47.250,0:07:48.720 negative oxygens here. 0:07:48.720,0:07:50.590 So they kind of want to push away from each other. 0:07:50.590,0:07:55.960 So these electrons in this bond really can't kind of get 0:07:55.960,0:07:57.220 close to the nucleus. 0:07:57.220,0:07:59.670 They'll go into kind of a low energy state. 0:07:59.670,0:08:03.000 All of this is more of an analogy than the reality. 0:08:03.000,0:08:05.210 We all know that electrons can get quite complex. 0:08:05.210,0:08:07.430 And there's a whole quantum mechanical world. 0:08:07.430,0:08:08.380 But that's a good way to think of it. 0:08:08.380,0:08:10.840 That these molecules want to be away from each other. 0:08:10.840,0:08:13.330 But you have these bonds, so this electron, it's kind of in 0:08:13.330,0:08:14.395 a high energy state. 0:08:14.395,0:08:17.250 It's further from the nucleuses of these two atoms 0:08:17.250,0:08:18.580 than it might want to be. 0:08:18.580,0:08:22.220 And when you pop this phosphate group off, all of a 0:08:22.220,0:08:23.870 sudden these electrons can enter into a 0:08:23.870,0:08:25.110 lower energy state. 0:08:25.110,0:08:27.080 And that generates energy. 0:08:27.080,0:08:32.030 So this energy right here is always-- in fact in any 0:08:32.030,0:08:34.409 chemical reaction where they say energy is generated, it's 0:08:34.409,0:08:37.200 always from electrons going to a lower energy state. 0:08:47.510,0:08:48.570 That's what it's all about. 0:08:48.570,0:08:50.610 And later in future videos when we do cellular 0:08:50.610,0:08:54.480 respiration and glycolysis and all that, whenever we show 0:08:54.480,0:08:57.330 energy, it's really from electrons going from 0:08:57.330,0:08:59.900 uncomfortable states to more comfortable states. 0:08:59.900,0:09:02.640 And in the process they generate energy. 0:09:02.640,0:09:05.620 If I'm in a plane or I'm jumping out of a plane, I have 0:09:05.620,0:09:07.180 a lot of potential energy right when I 0:09:07.180,0:09:08.050 jump out of the plane. 0:09:08.050,0:09:10.280 And you can view that as an uncomfortable state. 0:09:10.280,0:09:13.350 And then when I'm sitting on my couch watching football, I 0:09:13.350,0:09:15.690 have a lot less potential energy, so that's a very 0:09:15.690,0:09:16.500 comfortable state. 0:09:16.500,0:09:18.790 And I could have generated a lot of energy 0:09:18.790,0:09:20.480 falling to my couch. 0:09:20.480,0:09:21.590 But I don't knows. 0:09:21.590,0:09:24.540 My analogies always break down at some point. 0:09:24.540,0:09:28.230 Now, the last thing I want to go over for you is exactly how 0:09:28.230,0:09:29.530 this reaction happens. 0:09:29.530,0:09:32.410 So far you could turn off this video and you could already 0:09:32.410,0:09:35.680 deal with ATP as it is used in 95% of biology, 0:09:35.680,0:09:36.790 especially AP Bio. 0:09:36.790,0:09:38.630 But I want you to understand how this 0:09:38.630,0:09:40.320 reaction actually happens. 0:09:40.320,0:09:43.110 So to do that, what I'm going to do is copy and 0:09:43.110,0:09:44.150 paste parts of these. 0:09:44.150,0:09:46.170 So I already told you that this guy right here is going 0:09:46.170,0:09:51.280 to break off of the ATP. 0:09:58.490,0:10:01.030 So that's the phosphate group that breaks off. 0:10:01.030,0:10:02.360 And then you have the rest of it. 0:10:02.360,0:10:05.310 You have the ADP that's left over. 0:10:05.310,0:10:07.530 So this is the ADP. 0:10:07.530,0:10:09.340 I don't even have to copy and paste all of this stuff. 0:10:09.340,0:10:12.000 You can just accept that that's the adenosine group. 0:10:18.050,0:10:19.500 Just like that. 0:10:19.500,0:10:22.240 So we've already said that this thing gets hydrolyzed 0:10:22.240,0:10:24.930 off, or gets cut off and that generates energy. 0:10:24.930,0:10:25.770 But what I want to do is actually 0:10:25.770,0:10:28.300 show you the mechanism. 0:10:28.300,0:10:30.260 A little bit of hand-wavy mechanism of how 0:10:30.260,0:10:31.630 this actually happens. 0:10:31.630,0:10:34.825 So I said this reaction occurs in the presence of water. 0:10:34.825,0:10:37.210 So let me draw some water here. 0:10:37.210,0:10:40.040 So I have an oxygen and a hydrogen. 0:10:40.040,0:10:42.100 And then I have another hydrogen. 0:10:42.100,0:10:43.710 That's water right there. 0:10:43.710,0:10:47.360 So hydrolysis is just a reaction where you say, hey, 0:10:47.360,0:10:51.420 this guy here, he wants to bond with something or he 0:10:51.420,0:10:53.920 wants to share someone else's electrons. 0:10:53.920,0:10:58.500 So maybe this hydrogen right here goes down here and shares 0:10:58.500,0:11:02.250 its electron with this oxygen right here. 0:11:02.250,0:11:06.320 And then this phosphorus, it has an extra electron that it 0:11:06.320,0:11:06.820 needs to share. 0:11:06.820,0:11:09.190 Remember it has five valence electrons; it wants to share 0:11:09.190,0:11:10.360 them with oxygen. 0:11:10.360,0:11:14.040 It has one, two, three, four being shared right now. 0:11:14.040,0:11:17.670 Well, if this hydrogen goes to this guy, then you're left 0:11:17.670,0:11:19.980 with this blue OH right here. 0:11:19.980,0:11:22.460 And this guy can share one of the 0:11:22.460,0:11:24.810 phosphorus' extra electrons. 0:11:24.810,0:11:27.190 So you get the OH just like that. 0:11:27.190,0:11:29.230 So that's the actual process that happens. 0:11:29.230,0:11:31.350 And it could go the other way as well. 0:11:31.350,0:11:33.040 I could've cleaved it here. 0:11:33.040,0:11:34.740 I could have cleaved the whole thing here. 0:11:34.740,0:11:37.270 And so this guy would have kept the oxygen and the 0:11:37.270,0:11:38.890 hydrogen would have gone to him. 0:11:38.890,0:11:40.820 And then this guy would have taken the OH. 0:11:40.820,0:11:42.540 It could happen in either order. 0:11:42.540,0:11:44.765 And so either order would be fine. 0:11:44.765,0:11:47.010 And there's one other point I want to make. 0:11:47.010,0:11:48.435 And this is a little bit more complex. 0:11:48.435,0:11:50.930 And I was even wondering whether I wanted to make it. 0:11:50.930,0:11:53.310 My whole reason why you're kind of in a lower energy 0:11:53.310,0:11:56.510 state is, once you break apart--actually let me go 0:11:56.510,0:12:00.370 down here-- is because I said, hey, this electron is happier 0:12:00.370,0:12:03.090 when it's-- so let's say this electron that was part of this 0:12:03.090,0:12:04.760 phosphorus is happier now. 0:12:04.760,0:12:06.540 It's in a lower energy state because 0:12:06.540,0:12:07.950 it's not being stretched. 0:12:07.950,0:12:10.350 It's not having to spend time between that guy and that guy 0:12:10.350,0:12:13.050 because this molecule and this molecule want to spread apart 0:12:13.050,0:12:14.560 because they have negative charges. 0:12:14.560,0:12:15.910 That's part of the reason. 0:12:15.910,0:12:18.410 The other reason why, and we'll talk about this in a lot 0:12:18.410,0:12:21.540 more detail when we learn more about organic chemistry, is 0:12:21.540,0:12:23.940 that this has more resonance. 0:12:23.940,0:12:27.770 More resonance structures or resonance configurations. 0:12:27.770,0:12:31.360 And all that means is that these electrons, these extra 0:12:31.360,0:12:34.240 electrons here, they can kind of move about between the 0:12:34.240,0:12:37.170 different atoms. And that makes it even more stable. 0:12:37.170,0:12:40.910 So if you imagine that this oxygen right here has an extra 0:12:40.910,0:12:42.700 electron with it. 0:12:42.700,0:12:47.840 So that extra electron right there, it could come down here 0:12:47.840,0:12:51.180 and then form a double bond with the phosphorus. 0:12:51.180,0:12:54.810 And then this electron right here can then jump back up to 0:12:54.810,0:12:55.870 that oxygen. 0:12:55.870,0:12:58.400 And then that could happen on this side and on that side. 0:12:58.400,0:12:59.990 And I won't go into the details, but that's another 0:12:59.990,0:13:01.800 reason why it makes it more stable. 0:13:01.800,0:13:03.590 If you've already taken organic chemistry, you can 0:13:03.590,0:13:05.080 kind of appreciate that more. 0:13:05.080,0:13:07.570 But I don't want to get all into the weeds. 0:13:07.570,0:13:11.120 The most important thing to remember about ATP is that 0:13:11.120,0:13:14.460 when you cleave off a phosphate group it generates 0:13:14.460,0:13:17.950 energy that can drive all sorts of biological functions, 0:13:17.950,0:13:20.570 like growth and movement, muscle movement, muscle 0:13:20.570,0:13:23.900 contraction, electrical impulses in 0:13:23.900,0:13:25.290 nerves and the brain. 0:13:25.290,0:13:29.310 So this is the main battery or currency of energy in 0:13:29.310,0:13:32.540 biological systems. That's the main thing that you really 0:13:32.540,0:13:33.790 just need to remember about ATP.