Specifically, that club-headed myosin wants to get all up-close-and-personal with the actin.

具体来说，棒状头肌球蛋白想近距离接触肌动蛋白。

They've got their own famous coupling — a pretty pair of tiny protein strands called actin and myosin.

它们有自己著名联——漂亮微小蛋白质链，叫做肌动蛋白和肌球蛋白。

Like the actin and myosin in our muscles that enable us to move.

就像我们肌肉中肌动蛋白和肌球蛋白样，它们使我们能够移动。

Actin and myosin, the proteins of muscles, permit those bodies to move around.

肌动蛋白和肌球蛋白， 肌肉蛋白质， 允许这些身体四处移动。

But the only myosin heads that can bind to those newly exposed sites are ones that are ready for action.

但是唯能与这些新露部位合肌球蛋白头是那些准备好行动。

At this point, the myosin is totally stoked, because the bodyguards that have been frustrating it are in for a big, irresistible distraction.

在这点上，肌球蛋白完全兴奋起来，因为直让它沮丧保镖会有个巨大、可抗拒分心。

They're divided lengthwise into segments called sarcomeres, which contain two even tinier strands of protein — two different kinds of myofilaments called actin and myosin.

它们在纵向上被分成称为肌节部分，其中包含两股更小蛋白质——两种肌丝称为肌动蛋白和肌球蛋白。

A sarcomere contains both thin filaments, made up mostly of two light and twisty actin strands, and thick filaments, composed of thicker, lumpy-looking myosin strands.

肌节既包含细丝，主要由两条轻盈而扭曲肌动蛋白链组成，也包含粗丝，由更厚、看起来块状肌球蛋白链组成。

Then comes a brief period of contraction, when the myosin heads are binding, and pulling, and releasing, over and over, and the muscle fibers contract.

然后是短暂收缩，这时肌球蛋白头遍又遍地合、拉动和释放，肌肉纤维收缩。

When those channels are thrown open, the calcium stored inside rushes into the rest of the cell, and finally myosin is like, YES! Here we go!

当这些通道打开时，储存在其中钙会涌入细胞其余部分，最后肌球蛋白就像，是！开始了！

So after all that, with the myosin primed for action and the bodyguards out of the way, the myosin finally binds to actin, and it is beautiful.

经过这切，当肌球蛋白准备好行动，保镖离开，肌球蛋白最终与肌动蛋白合，这真是太美了。

That tension means myosin and the calcium pumps are burning up the muscle cells' ATP, and the finite supply of ATP is what makes it impossible to maintain vigorous muscle activity indefinitely.

这种张力意味着肌球蛋白和钙泵正在燃烧肌肉细胞三磷酸腺苷，而三磷酸腺苷有限供应使得肌肉活动可能无限期地保持旺盛。

But soon the fiber slides back down into the relaxation period, when the calcium gets pumped back into the sarcoplasmic reticulum, and the actin and myosin stop the binding cycle, and the muscle relaxes.

但很快，纤维滑回松弛期，此时钙被泵入肌浆网，肌动蛋白和肌球蛋白停止合循环，肌肉放松。

If another action potential travels down before that can happen, even more calcium gets released, which ends up exposing more actin for myosin to bind to, and that means more force in that fiber.

如果另个动作电位在此之前下降，更多钙被释放出来，最终露出更多肌动蛋白来合肌球蛋白，这意味着纤维中有更多力量。

You'd also re-learn that your skeletal muscles are constructed like a rope made of bundles of protein fibers, and that the smallest strands are your actin and myosin myofilaments.

你还会重新了解到你骨骼肌就像根由成束蛋白质纤维组成绳子，最小链是你肌动蛋白和肌球蛋白肌丝。

That binding causes another shape change. But this time, it causes the myosin to release from the actin, in a tear-jerking scene like some microscopic re-creation of the finale from Titanic.

这种合导致了另种形状变化。但这次，它导致肌球蛋白从肌动蛋白中释放出来，这是个催人泪下场景，就像泰坦尼克号局微观再现。

Because this is when the myosin breaks down its new molecule of ATP into ADP and a phosphate, which moves it into the armed position yet again, getting it ready for its next rendezvous.

因为这是肌球蛋白将其新 ATP 分子分解成 ADP 和磷酸盐时候，这使它再次处于武装状态，为下次会合做好准备。

When they bind, the myosin releases all that stored energy, and — in the excitement of it all — the myosin changes shape. It pulls on its precious actin strand, kind of like pulling a rope hand over fist.

当它们合时，肌球蛋白释放所有储存能量，在兴奋中，肌球蛋白改变形状。它拉着它珍贵肌动蛋白链，有点像用手握住拳头拉绳子。

So the calcium latches on to the troponin and causes it to pull the other bodyguard protein — the tropomyosin — away from the sites on the actin strands that the myosin really wants to get its paws on.

所以钙锁住肌钙蛋白，并使其将另种保护蛋白——原肌球蛋白——从肌球蛋白真正想要抓住肌动蛋白链上位置拉走。

When a myosin head does that, it moves into an extended position, kinda like a stretched spring — still holding on to the ADP and phosphate, and still storing the energy that was released when they were broken apart.

当肌球蛋白头这样做时，它会移动到伸展位置，有点像被拉伸弹簧——仍然抓住 ADP 和磷酸盐，仍然储存它们破裂时释放能量。