Musculoskeletal System | Sarcomere Structure: Actin & Myosin – Transcript

00:06our engineers so in this video we're going to continue on with what we finished up with so if you guys remember we talked in the recent video in part one which if you guys haven't seen that you guys got to go and watch that first ok then we're going to go over in this next video we're going to talk a little bit more about the myofibril so in the recent video we took a skeletal muscle right we took that belly we've made a transverse cut we look at that transverse cut and we saw the connective tissue coverings that are surrounding each layer right so for example the

00:34muscle belly is covered by a connective tissue called the epimysium then inside of that muscle belly we have these things called fascicles and fascicles are just bundles of muscle fibers and then each one of these are a fascicle all right and then around them around that fascicle you have a nice connective tissue covering which we showed right here that was called the perimysium then in this fascicle there's individual muscle fibers what we did is we pull one of those muscle fibers out which again

01:01you can call muscle fiber a muscle cell there's a connective tissue covering that muscle fiber which is called the endomysium which is an areola connective tissue and then we said that you have a lot of dis filamentous filamentous endoplasmic reticulum structure which we call the sarcoplasmic reticulum it's a nice calcium storage Factory we said that striated which means it's striped and that's do this actual connection of thin and thick filaments that we'll talk about which is going to be making up the

01:29basic functional unit called the sarcomere and then we said it's multinucleated and we said that the muscle fibers are cylindrical and we said each muscle fiber is surrounded by a plasma membrane which we call the sarcolemma ok then we took and there's thousands hundreds upon thousands of these myofibrils which are just many many different connections of fixed elements and thin filaments and accessory proteins that we'll talk about

01:54and that is our myofibrils and what we did is we zoomed in on a portion of a myofibril and now we're going to talk about that all right so first thing that we're going to do is I'm going to lay out some different zones and regions and stuff like that because that's going to help us to continue to keep narrowing down protein after protein because literally that's all this whole basic myofibrils composed up as proteins so let's do that first

02:20so the first thing I'm going to do is if you see this pink just exact protein going all the way up this protein is actually going to be called the Z disk okay that's the Z disk and we'll talk about what protein it's made up in just a second on this one over here this is another zigzagged protein and we're going to call this one a z disk from

02:48z-disk to z disk is your functional unit of the muscle fiber right and the Z is to Z disk this is called the sarcomere from this Z disk point here so let's say I go from this point here from that z-disk all the way over here - that's Z disk this whole length is consisting of the structural and functional unit of this

03:15myofibril and that is called the sarcomere okay that is our sarcomere and the sarcomere is again the distance from Zedek to z disk now in that circle mirror there's a couple other structures that I need to talk about in this we have this thick thick filament this red thick filament this big rectangular box that big rectangular box there is called the thick filament and gets called the

03:42thick filament so again what is this red box right here that right there is specifically called the thick filaments all right now the thick filament if you look here's this whole thick filament right here this thick filament on this end you see these blue these nice little baby blue proteins right here they're linking this thick filament to this z

04:09disc and the same way these proteins are linking this thick filament to that V disc the same situation is happening over here look at the end of this thick filament you have these nice clearly like blue proteins linking the thick filament to the Z disc as well as this protein is moving through the thick filament and linking it to these green proteins running right down the middle of the sarcomere alright these blue

04:36proteins right here are called chitin alright chitin so this protein right here is specifically called chitin all right it's called chitin so these blue proteins right here called Titan and they're very special we'll talk about why they're special in just a second okay but again remember the Titans are anchoring the sixth element to the Z disk also they're connecting to these proteins that are running right down the

05:03middle part of the sarcomere what do these proteins here call well first off before we name these proteins what is this whole line here call this line right here is specifically referred to as the M line so these proteins here all the way up makes the M line alright so there's a bunch of a bunch of different proteins and as you look at one watch the M line as it goes up M line goes up goes up

05:30goes up and it connects to what is this protein Titan okay so if you look the M line which is running right up the middle of the actual sarcomere which is consisting of two main proteins we'll talk about a second is linking the actual Titan also to it so if you look this is connecting to the Titan what's the titan connecting it's connecting the stick filament to the actual z disk so Titan is helping to stabilize the thick filament and it can do that by not only

05:58anchoring it to the Z this but also anchoring it to these accessory protein structure called the M line whatever proteins is the M line made up of the main one that's made up of is called my Oh Mason my Oh Mason so my own Eason is one of the main proteins that is a part of the end line there's also C proteins

06:20there's another really important protein which is called creatine kinase but it's more of a functional protein rather than a structural protein but they are scattered along the m1 so these are three really really important proteins that are making up the M line and one of the proteins is called my Oh Mason the second one is called C proteins and the other one is called creatine kinase but again increasing

06:46kinase I'll star this one and the reason why is because it's more of a functional enzyme we'll talk about that when we talk about the metabolic actions of muscle fibers okay now again what's the function of the M line the M line is responsible for connecting these are accessory proteins it's connecting the Titan and the Titan is connecting the stick filament to the z-disks so it's acting as accessory proteins that can

07:12help to stabilize the thick filament that's their function Titan what do we say was the function of Titan it's actually stabilizing the thick filament by anchoring the sixth element to the z disc and it's also connecting with these accessory proteins of the M line all right sweet now here's the next thing from the end of this thick filament to the end of this thick filament we call this AB and it appears like a like a nice dark band when you look at it there

07:39so let's what is this band distance right here let's say I come from this point about right down here so I'm going to go from about right here all the way to about over here this whole distance right here is consisting of what's called the a band okay and the a band

08:05stands for an isotropic and isotropic hair I'll write that for you for those of you who want to know it and all it means is just a darker it's means that's a dark band okay so an isotropic just means it's a dark band so the a band is the entire length of the thick filament okay now from this thick filament end to this thick filament end over here I'm

08:31going to come down here I'm going to go from this point here to about approximately this point right here so now I'm going to come down from this point to this point so I'm going to continue off of this point I'm going to come to about right here approximately let's make this one blue we'll go to about right here it's not perfect but it's approximate this is called D I band okay this is

08:56called the I band and the I band specifically stands for it stands for isotropic okay so it stands for isotropic which just means it's a lighter color okay so it's same thing over here we follow it over here coming down from this point here approximately to about this point right here approximately this point right here is called the I band and again I stands for

09:24isotropic if you want to know that I'll write that down there for you it stands for isotropic and that just means again that it's a lighter color okay so I'll write isotropic over here for you guys too so so far what do we know we know we have a sarcomere which is from z-disk to z disk we know that we have an M line which is a protein running right down the middle of the

09:50sarcomere which is consisting on miami's and c proteins increasing kinase we also know that you have this stick filament and from one end of the thick filament to the other end of the sixth element is an a band standing for an isotropic which just means that it's a dark band on this end of this thick filament to the end of this thick filament on another sarcomere so for example this is a sarcomere here right we'll call this

10:17sarcomere one on sarcomere two over here could be sarcomere one so on sarcomere one from this end of this thick filament on sarcomere two to the actual end of this thick filament on sarcomere one that distance right there is the eye bent and the eye band stands for isotropic which means it's a lighter color okay now if you look here we have a whole bunch of proteins coming off of

10:44this bad boy right here this big big protein structure right here we're going to call this whole thing to thin filament okay so we're going to call this whole component here this whole all this blue the orange the green the black this is all the thin filament all right now the thin filament is directly connected to the Z disk through this black protein that's running right

11:11down the actual middle of its building the foundation for it that black protein that's running right down the middle of this is called nebula so again you can see right here so this is a thin filament this is a piece of a thin filament that's a thin filament and this is a thin filament and again connecting this thin filament to the Z disk is this black protein right again what is that black protein they're called this black protein is specifically called nebula

11:38okay nebula is a protein that's anchoring this whole thin filament structure to the z disk all right now you see these blue proteins right here that's making like a nice little supra molecular helix that's called actin but here's the thing with actin there's two types of actin mainly so we're going to talk about so let's say I take one of those individual structures they're just one individual circle that one

12:06individual circle that kind of like kidney bean-shaped if you actually look at it in a normal way it's actually called g actin so a monomer of actin is called g act let me write that down this is a monomer but then let's say i polymerize this bad-boy and when undergoes this polymerization let's say i take a whole bunch of these badboys a whole bunch of these g actin molecules

12:32and connect them together if I start doing this now now this is called F actin okay so now this is called F acting now what happens is when I take this G actin and I make this new actin called it's called the filament asia's acting or I just like to call it the filamentous actin and then G stands for globular actin so when I go from globular actin to filament it actin it's

12:59just because I'm polymerizing these guys so this is a polymerization reaction now all that happens is to just be simple let's say this is a monomer of F actin and I take another monomer of F actin and I take and make a helix like structure and that's what you see here for this Acton okay so when you look at this act in here it's looking like a supramolecular helix which is