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Current time:0:00Total duration:7:31

Video transcript

so ever since I first learned about myosin and actin there was always this kind of thought that popped in my head kind of an analogy if you will and for a long time I thought this analogy was pretty much spot-on but then I I gave it some more thought and I realized that I was wrong and so I'm going to share with you what my analogy had always been and you'll see I'm sure pretty quickly why I was mistaken so let me start out by just drawing out the actin and myosin this is of course in red the actin and in purple I've got my myosin this will be my myosin here and this is of course three different myosin and actin so I'm going to draw for you I'm going to show different stages of how they could look this one is a little bit more stretched out here and I'll draw like that and the final one will be very very stretched that will actually just kind of get almost off this screen something like this so these are my three actins and myosins and we know if we were to actually take a step back maybe I could even label them ABC let's call this one a let's call this one B and the third one will be C so we've got our a B and C and you know there's this kind of a helpful way of looking at this stuff we call it the tension lengths curve so I'll put tension over here and this is of course kind of a unit of force thinking about how forcefully something is contracting and then over here let me actually erase that over here we have sarcomere lengths right so these are our two axes and on the on the graph we can quickly just kind of put where a B and C would lie so you can see that based on the way that I've drawn this stretch I'm just going to kind of divide this in half based on the way I've drawn it out a is actually going to have almost no force right that's going to be the the conclusion we can reach it's going to be something like this and then B will be somewhere up here let's draw a B right here because there's going to be a lot of force there and C will be I'll draw it right here at the edge also almost no force and you remember that this actually falls on a kind of curve that we drew up before something like this where actually I didn't draw all the points but it kind of goes like that so this is our tension length curve and you can see where a B and C kind of fit on that curve now on the side what I wanted to draw on the other side I'm going to draw out kind of what my analogy used to be the way I used to think about it and it also kind of breaks down into an ABC and I'll just write it out here and it's something that I always used to play with as a kid I always used to love slingshots and so I'm going to draw three slingshots one two three and each one will actually have a rubber band attached to it and I'm going to stretch it out to different lengths so let's say this first one I kind of don't stretch much at all and then the second when I stretch really far as far as I can and then this third one I stretch it so far that it kind of snaps and of course if I have a slingshot I need a stone so I'm going to put my purple stone right there and I'll put my purple stone right there at the tip and then this purple stone I guess I have to kind of hold it as always it would just fall down right so what would happen if I actually now tried to plot out on this side on the right side of your screen if I plot it out similar to kind of the tension length but in this case I would put said attention let's put distance and this would be like the distance traveled of my stone so maybe I can rewrite this and make it a little bit more roomy so distance of my stone traveled and that'll be here and then I can also on the x-axis I can put something like how much I stretched my rubberband I'll just put let's say stretch and you'll know that that means how much I stretched out the rubber band on my slingshot now if I actually let go of all three the stone would probably fall right there on a and it would fall right there on C but for B it would kind of launch try to launch away and so in terms of distance I can actually kind of plot that out I could say well you know for a I had almost no you know distance I would say zero distance you know and for C kind of the same thing I would say really no distance but for B I had a lot of distance so I actually did really well with B and this is kind of how I always thought about the heart I always thought well you know it's very similar some ways to a slingshot you know you have kind of an up and down right and so I always kind of walked around with that idea but I gave it some more thought recently and I was thinking you know is this really accurate and I think the answer is no and let me show you why so on the slingshot side let's do this side first well what do we have exactly we have elastic energy elastic energy and that's just the elastic in the band but there is energy stored up there because it's the sort of potential energy it's actually very similar to what happens in our arteries where you store up energy in our elastic large arteries like the aorta we have this elastic energy and when you let go of the stone what basically happens is that you convert all that to kinetic energy right so you're converting it all to kinetic energy move energy of movement and when you let go of that stone it happens automatically so you really don't have to put energy into it because you already had elastic energy was already stored up so in that sense we often think of this process and this is actually kind of the important part we often think of this process is being passive so you'll often see the word passive put that down here passive and that simply means that we didn't have to add any energy but specifically the kind of energy we're talking about is chemical energy so when bills say there's a passive process usually in biology what we're talking about is not having to use chemical energy and of course in the slingshot example there was no chemical energy used but in my heart example in my sarcomere there was chemical energy in fact what we're really doing is we're converting chemical energy and specifically the type of chemical energy we're talking about if you remember is ATP remember all those myosin heads are working in grinding through ATP so this is really ATP energy that we're burning through and we're creating again kinetic energy sometimes I call it mechanical energy but both times what I mean with kinetic or mechanical energy is to say that you basically have the heart pumping you actually have movement of the heart and the way that you're getting is by burning through all this ATP so in that sense because we're burning eight oftentimes in biology we call this kind of an active process now in both cases you're just changing one form of energy to another so it's not like I was completely wrong with my thought process I mean it was there are some strong similarities and at the end of the day both of them are creating movement so there is a similarity there you're changing energy forms and you're creating movement but the key difference is in what type of energy we're starting with and I want to make sure it's very very clear that with the heart it often looks like a rubber band it even kind of sometimes feels like it could be like a rubber band where you're stretching out but really never forget that the myosins are grinding through ATP and that that is the way that you're actually able to create the kinetic energy whereas in an elastic band you're actually using elastic energy so that's the key difference