Muscle Physiology: Troponin, Tropomyosin, and Myosin Cross-Bridge Cycle
Summary
TLDREste vídeo se enfoca en el ciclo de la puente cruzada (crossbridge cycle), un proceso esencial en la contracción muscular. Se explica cómo los músculos se contraen al acortarse, utilizando un enfoque kinésico para visualizar mejor los movimientos. Se detalla cómo las miofibrillas, las unidades funcionales del músculo, se contraen al formar puente cruzadas entre las proteínas de la miosina (espesas) y la actina (delgadas). La contracción se desencadena con la liberación de calcio, que permite que la miosina se una a la actina y realice el paso de potencia, acortándose y moviendo las filamentos hacia la línea M. El vídeo utiliza animaciones para ilustrar este proceso a nivel molecular.
Takeaways
- 💪 El vídeo trata sobre el ciclo de crossbridge, un proceso esencial en la contracción muscular.
- 🤔 Se utiliza una aproximación más práctica y visual para enseñar cómo se mueven las partes musculares durante la contracción.
- 📐 Se explica que, al contraerse, el bíceps brachii se encoge, disminuyendo el ángulo en la articulación del codo.
- 🔬 Se detalla que cada célula muscular está compuesta por unidades funcionales llamadas miofibrillas, y dentro de estas, las unidades funcionales son los sarcómeros.
- 🧬 Los filamentos gruesos, formados por la proteína miosina, y los filamentos delgados, formados por actina, son cruciales en el ciclo de crossbridge.
- 🔴 Los filamentos gruesos contienen miosina, una proteína contractile y enzima que causa la contracción muscular.
- 🟡 Los filamentos delgados contienen actina, y tienen sitios de unión para miosina, esenciales para formar el crossbridge.
- ⚪️ El proceso de contracción comienza con la liberación de calcio, que permite que la miosina se una a la actina, iniciando el ciclo de crossbridge.
- 🔄 La ATP desempeña un papel crucial en el ciclo de crossbridge, causando la desconexión de la miosina de la actina y su posterior activación.
- ➡️ El 'power stroke' es el movimiento por el cual la miosina contrae y se adentra en la actina, lo que resulta en la contracción muscular.
Q & A
¿Qué es el ciclo de crossbridge y cómo se relaciona con la contracción muscular?
-El ciclo de crossbridge es el proceso por el cual las proteínas miosina y actina interactúan para causar la contracción muscular. Las cabezas de la miosina se unen a los sitios de unión de la actina, se activan y realizan un 'paso de fuerza' que provoca el movimiento de las filamentas hacia la línea M, resultando en la contracción del músculo.
¿Cuál es la función de las miofibrillas dentro de una célula muscular?
-Las miofibrillas son las unidades funcionales dentro de una célula muscular que permiten la contracción. Están compuestas de filamentos gruesos (miosina) y delgados (actina) que se mueven en relación durante el ciclo de crossbridge.
¿Qué es un sarcómero y cómo se relaciona con el movimiento muscular?
-Un sarcómero es la unidad funcional microscópica dentro de una miofibrilla. Es el segmento de la miofibrilla que se encarga de la contracción y se encorta hacia la línea M durante la contracción muscular.
¿Qué proteínas componen los filamentos gruesos y delgados en un sarcómero?
-Los filamentos gruesos están compuestos principalmente de la proteína miosina, mientras que los filamentos delgados están compuestos de actina.
¿Qué es la función de la miosina como enzima y cómo se relaciona con la contracción muscular?
-La miosina actúa como una enzima que cataliza la hidrólisis de ATP, lo que libera energía para la contracción. La miosina se une a la actina utilizando la energía de ATP, lo que inicia el ciclo de crossbridge y resulta en la contracción.
¿Qué sucede cuando la miosina se une a la actina durante el ciclo de crossbridge?
-Cuando la miosina se une a la actina, se forma un crossbridge que permite la transferencia de energía de la hidrólisis de ATP a un movimiento mecánico, lo que provoca el movimiento de las filamentas actina hacia la línea M y la contracción del músculo.
¿Qué es el papel de ATP en el ciclo de crossbridge?
-ATP es esencial en el ciclo de crossbridge porque provee la energía requerida para la contracción. Se hydroliza en ADP y fosfato, lo que permite que la miosina se active y realice el paso de fuerza necesario para la contracción.
¿Cómo se desencadena la contracción después de la hidrólisis de ATP?
-Después de la hidrólisis de ATP, la liberación de energía activa la cabeza de la miosina, que se coloca en una posición lista para unirse a la actina. La liberación del fosfato y ADP de la miosina intensifica la unión miosina-actina y desencadena el paso de fuerza que resulta en la contracción.
¿Qué es el papel de la troponina y la tropomiosina en la regulación de la contracción muscular?
-La troponina es una proteína que se une al calcio, lo que permite que la tropomiosina se desplace y revele los sitios de unión de la miosina en la actina. Esto es esencial para iniciar el ciclo de crossbridge y la contracción muscular.
¿Cuál es el significado de la línea M en un sarcómero y cómo se relaciona con la contracción?
-La línea M es el punto central de un sarcómero y es hacia donde se mueven las filamentas actina durante la contracción. La contracción se produce cuando las filamentas actina se desplazan hacia la línea M debido a la acción de las cabezas de la miosina.
Outlines
💪 Ciclo del puente cruzado en la fisiología muscular
Este vídeo se centra en el ciclo del puente cruzado, un concepto clave en la fisiología muscular. Se utiliza una aproximación más dinámica y visual, en lugar de presentaciones tradicionales, para ilustrar cómo se mueven las partes musculares. Se explica que, al contraerse, el bíceps se encoge y se reduce el ángulo en la articulación del codo. Se invita al espectador a realizar un ejercicio físico para experimentar este cambio. Se detalla la composición del músculo, mencionando las células musculares, las miofibrillas y los sarcómeros. Se enfatiza la importancia de la interacción entre las proteínas miosina (filamentos gruesos) y actina (filamentos delgados), y cómo esta interacción es crucial para el movimiento muscular.
🔬 Funcionamiento a nivel molecular del ciclo del puente cruzado
Se profundiza en el proceso molecular del ciclo del puente cruzado, destacando la función de la miosina y la actina. Se describe la aparición de iones de calcio que activan la contracción muscular al interactuar con las proteínas troponina y tropomiosina, exponiendo los sitios de unión de miosina en la actina. Se ilustra cómo la ATP (adenosín trifosfato) desempeña un papel crucial en el ciclo: su hidrólisis provoca la activación de la cabeza de la miosina, preparándola para unirse a la actina y formar un puente cruzado. Este proceso es esencial para el movimiento de los filamentos musculares y, por ende, para la contracción muscular.
🏋️♂️ Detalles del proceso de contracción muscular
Se explica con detalle el proceso de contracción muscular, que comienza con la formación de un puente cruzado entre la miosina y la actina. La llegada de ATP provoca la desconexión de la miosina de la actina. Posteriormente, la hidrólisis de ATP y la liberación de energía activan la cabeza de la miosina, preparándola para unirse nuevamente a la actina. Se describe cómo la liberación de fosfato y ADP incrementa la fuerza de la interacción miosina-actina y desencadena el poderoso movimiento de la cabeza de la miosina, conocido como el 'pase de fuerza'. Este movimiento es responsable de la contracción muscular y se visualiza a gran escala en el vídeo, mostrando cómo los filamentos delgados se mueven hacia la línea media del sarcómero.
Mindmap
Keywords
💡Crossbridge cycle
💡Bíceps
💡Myofibril
💡Sarcomero
💡Filamentos gruesos
💡Filamentos finos
💡ATP
💡Cálcium
💡Troponina
💡Tropomiosina
Highlights
视频专注于肌肉生理学中的交叉桥循环(crossbridge cycle)
交叉桥循环的教学采用动态展示,以增强理解
二头肌收缩时肌肉缩短的演示
肌肉细胞内的功能性单位称为肌原纤维(myofibrils)
肌原纤维的功能单位是肌小节(sarcomere)
肌小节缩短向M线(中间线)移动的过程
肌小节中的厚丝(thick filaments)主要由肌凝蛋白(myosin)构成
肌凝蛋白不仅是收缩蛋白,也是酶,其酶机制导致肌肉收缩
肌小节中的薄丝(thin filaments)主要由肌动蛋白(actin)构成
肌动蛋白上存在肌凝蛋白结合位点,是形成交叉桥的关键
钙离子在肌肉收缩中的作用,与肌钙蛋白(troponin)结合
钙离子结合导致原肌球蛋白(tropomyosin)从肌凝蛋白结合位点移开
肌凝蛋白头部与肌动蛋白结合形成交叉桥
ATP分子的结合导致肌凝蛋白从肌动蛋白上脱离
ATP水解为ADP和无机磷酸盐,激活肌凝蛋白头部
磷酸盐的释放增强了肌凝蛋白与肌动蛋白之间的相互作用
ADP的解离导致肌凝蛋白头部发生强力的“动力冲程”
肌凝蛋白头部的收缩是人体生物化学中最大的构象变化之一
多个肌凝蛋白分子连续作用,拉动肌动蛋白丝向M线移动
Transcripts
welcome back to the muscle physiology
playlist this is going to be a video
dedicated to what we call the
crossbridge cycle and I'm kind of taking
a deviation here from uh the normal uh
paintbrush and PowerPoint videos because
quite honestly um it's a lot more
effective in terms of teaching this
stuff if you can if you can physically
see how things are moving um you know
from class I like to give you more of a
kinesthetic approach to this okay so
what you see here is what's referred to
as the bicep break eye other muscles
have been um eliminated for clarity
purposes okay and what's going to happen
is when the bicep break eye contracts it
shortens okay so this is a good place to
pause it and I want to do a little
exercise with you so I want you to have
your arm starting out in the extended
position so in other words where the
angle between your humoris and your
radius and on is 180 de and I want you
to put your hand on your bicep at least
at the point where it sort of um kind of
gets close to the elbow and keep your
hand on that point and then what I want
you to do is I want you to flex your arm
in other words by a flexion I mean
rotate your elbow such that you decrease
the angle of the joint like they showed
just now in the video and what you'll
find is that your muscle actually
shortens so what you see here is more in
the extended position and then what you
see is the bicep contract and what that
means is is that the bicep is shortening
as a whole well the question remains is
how does the bicep shorten overall well
it turns out that each of the muscle
cells that makes up the muscle as a
whole each muscle cell has functional
units called
myofibrils okay um the functional unit
of the myofibril if we get even more
microscopic is called the
sarir and what what we're going to do
here is we're going to look at the
function of the sarir and so let's
continue this
video so that's an extension of the arm
in which case the muscle lengthens okay
so now we're zooming in on this muscle
and we're going to look at what's
referred to as the crossbridge cycle
okay so here what we're doing is we're
looking at myof fibral this right here
is the sarir the functional unit and now
what we're doing is we're zooming in
right here and what they're going to
show you is these red filaments right
here these are called the thick
filaments now what's really important
here is the thick filaments have a major
protein it's a contractile protein
referred to as mein mein is not just a
contractile protein it's also an enzyme
and the enzymatic mechanism that it uses
is actually what causes it to contract
so the red ones or this pinkish ones are
going to be the thick filaments the
yellow ones that lie between the thick
filaments those are are the thin
filaments the major protein on those is
called actin and actually what we're
going to find is that on each actin
protein there's what we call a mein
binding site and so this is an important
Point here is that actin must bind to
mein or you could view it the other way
around in fact that's normally how
people view it they say that in order
for a crossbridge to form in the sarir
mein has to bind to actin and like I
said there's a mein binding site on
acted and we're going to look at the
events that occur on the sarir level
okay so what's essentially going to
happen here is you're going to see the
actin filaments right here move towards
this point where my mouse is so notice
notice my positioning of the mouse where
I'm going up and down this point on the
saram miror this line is called the M
line m stands for middle and the reason
it's called the mline is because the
sarcomere shortens toward this line
towards the mline in lab we looked at
that model we're going to look at it
again this week and you're going to see
how the sarir shortens towards this line
right here and in in reality what's
happening is the mein heads attached to
the actin or these thin filaments and
the thin filaments are going to get
walked ultimately towards this mline
okay so here they're showing the thick
filaments the thick filaments are going
to be the mein the thin filaments are
going to be the actin okay and notice
what happened let's go back back and
watch that process again notice how the
sarir is shortening toward the mline
okay so what's happening are those mein
heads which are located on the thick
filaments are walking the thin filaments
towards the mline let's watch that one
more time okay so notice this line right
here at this point the thin filaments
are being walked toward that line okay
so now let's take a look at what H
what's happening on the molecular level
so this right here you can see it right
here this is a little purple dot right
here you're going to see more of those
okay that is what's referred to as a
calcium ion in this video and you're
going to see more of them come by um
some other things that are important
these blue proteins right here these
circular blue proteins those are called
troponin and in a separate video we go
over the um the functionality of
troponin and troponin is a calcium
binding protein we'll see calcium bind
to this protein later on by the way the
thin filaments are composed of actin and
the actin are the kind of these yellow
dots that go around here and the yellow
dots are sort of wound together in a
helix and so the these yellow spherical
um repeating units are the thin
filaments and notice how the green
protein tropomyosin wraps around it in
in another helical type of arrangement
well it turns out that at rest the this
green protein called
tropomyosin tropomyosin covers up the
Myas binding sites on actin when the
calcium binds to the troponin what
you'll see is that the tropomyosin is
going to rotate off of The Binding sites
and you'll I think you'll see pretty
clearly what The Binding sites are as
soon as the tropomyosin rotates off of
the actin okay so what's going to happen
is this calcium and some others are
going to bind to these troponin
molecules that's going to cause
tropomyosin this green helical protein
to rotate off of the mein binding sites
on these actin um subunits of the thin
filament so hopefully you'll see that
right here so here comes the calcium
ions and you'll see some more come and
they're going to bind to troponin and
notice what's going to happen is the
tropo here's the troponin with the
calcium the tropomyosin which is in
green is going to rotate off of the mein
binding sites on actin okay so now
hopefully you see these little black
dots right here okay those are The
Binding sites for mein and and so what
you'll see is at certain points in the
mein cycle the mein can actually bind to
those sites so we're going to see how
that occurs now so what the mein head
will literally do is it will form an
attachment here with the thin filaments
okay so here's kind of the Assumption
we're going to make um here um when
we're looking at the cycle of mein so
this red thing right here that kind of
looks like a golf club in a sense this
is the mein head and this is sort of
literally what they look like they're
sort of in an arrangement like this so
what we're going to do in this video is
we are going to make the assumption that
the the cycle of mein begins with the
crossbridge okay the crossbridge is
essentially the the interaction or
binding of mein to the mein binding side
and actin meaning that masin and actin
are physically connected we're going to
start our cycle with that connection
there okay in other textbooks you may
see um the cycle begin at different
points this is just where I choose to
start the cycle so you're making an
assumption that you know this this
crossbridge is already formed okay
what's going to happen is there's going
to be a molecule of ATP that comes in
and you'll see that in just a minute so
this is the me head that molecule that
kind of looks like a pill that's coming
in that's representative of a Denine
triphosphate what you're going to see is
that when a Denine triphosphate binds to
the mein head it's going to cause
Detachment of mein from actin so let's
see how that occurs so ATP binds and
notice what happened you can there's
just a small Gap there but notice that
masin just detached from actin that's
what we call crossbridge Detachment okay
okay so now masin it's attached now that
little flash of light that occurred
there that was ATP
hydrolysis okay um what I recommend
doing if you're looking at this in the
context of organic and biochemistry is
I'll have another video on the mein um
mechanism that was actually recently
determined using quantum mechanics I
recommend that you go look at that that
particular mechanism and you'll kind of
see um how ATP relates to this but if
you go back and kind of watch that step
let's go back a little bit ATP gets
hydrolized into adenosine diphosphate
and inorganic phosphate okay what that's
going to do as you'll see now is it's
going to activ at the mein head and when
we say activate it typically what we
mean is it gets cocked into the
activated position so this position
right now where it is it's inactivated
but when you when you hydroly ATP you
release some energy in context of
chemistry we call that Gibbs free energy
and that energy is going to mein's
head into the activated position okay so
you'll see it kind of move into the
activated position assuming I hit play
okay there we go and the mein head is
going to get cocked into the activated
position okay so at this point right
here the mein head has bound ADP that's
this little bright yellow sphere has
bound phosphate that's the little red
sphere and so now masin is in the
activated position and it's going to be
able to bind to aasin binding site on
actin so let's continue okay so now what
we're assuming we're going to go back
and look at these steps in in kind of
the same detail so we're starting with
mein bound to actin okay so once again
we're going to kind of see the same
story so mein's bound to actin okay
what's going to happen ATP comes in and
causes crossbridge
Detachment okay so you'll see mein
detach from actin the next step is going
to be ATP hydrolysis ATP is going to get
hydrolyzed into a Denine diphosphate and
inorganic phosphate and that's going to
the mein head into the activated
position as shown there okay in this one
they call this step one but basically
what's going to happen now is the
crossbridge is going to form so myosin
is going to spontaneously bind to actin
and then what's going to happen is a
series of processes okay notice that
molecule that just left okay that's
phosphate it turns out that when
phosphate leaves the mein head okay it
strengthens the interaction between mein
and actin so what you're going to see
here is an Inc increase in the strength
of the mein actin interaction okay so
the strength is increased okay and then
what's going to happen something
referred to as the power stroke so the
first thing that happens is ADP
dissociates so when ADP dissociates from
the mein active site it's going to
result in a very strong Power Stroke as
you'll see here okay so hopefully you
can kind of see that contraction of the
mein head and one important thing to
kind of point out here is that um and
and somebody correct me if I'm wrong on
this in the comments but as far as I
know this movement of mein where it
where the where the head contracts and
moves the thin filament that movement
when ADP dissociates I believe is the
largest confirmational change in any
protein in human biochemistry so it's a
very large contraction with respect to
the total volume of this protein let's
watch that again cuz it's really
important kind of go back a little bit
so phosphate dissociates with which
which strengthens the mein actin
interaction and then ADP dissociates
from the mein active site and then what
you get is the power stroke notice the
contraction okay so hopefully that makes
a little bit of sense we're now going to
watch this in real time with a bunch of
mein molecules and they are they're
continuously in the presence of ATP
they're pulling the actin filaments
toward the mline so this is literally
what's happening go back here and
hopefully what you see is on a more
macroscopic scale the thin filaments are
going to be pulled toward the mline of
the sarir and that's all due to mein
contraction
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