During the contraction of a vertebrate skeletal muscle fiber, calcium ions
a. Break cross-bridges as a cofactor in hydrolysis of ATP
b. Bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed
c. Transmit action potentials from the motor neuron to the muscle fiber
d. Spread action potentials through the T tubules

Question

During the contraction of a vertebrate skeletal muscle fiber, calcium ions

a. Break cross-bridges as a cofactor in hydrolysis of ATP

b. Bind with troponin, changing its shape so that the myosin-binding sites on actin are exposed

c. Transmit action potentials from the motor neuron to the muscle fiber

d. Spread action potentials through the T tubules

Accepted Answer

Hello everyone. Let's look at our next question here. It says, what is the rule of troponin in muscle contraction. Well, as you might recall from our content videos. Troponin is a protein bound to another protein called trump a mission. And when the muscles are in a relaxed state, trophy missin blocks the binding site where medicine combined acting forming the cross bridges that allow muscle contraction. So it's kind of a lot of parts. So I'm just going to throw up a quick diagram here to help us remember this process as we evaluate our answers to look at the role of that troponin. So on the left side here this is our muscle in a relaxed state and here's our acting filament. Here's our troponin and it is connected here bound to the protein trouble missin missin. We see here blocking the area in Acton where the miocene would come in and bind to cause the muscle to contract. That's in a relaxed state. When the muscles stimulated to contract, we have these calcium ions released and we can see we've got a little binding site on troponin for calcium ions. So as that signal is released to get the muscle ready to contract Troponin bound to the calcium causes this trope of medicine to sort of roll away and expose that site, the miocene can come in and bind to the act in forming the cross bridges that allow the muscles to contract. So let's go through the answer choices to find the best description after opponents. Roll choice a says it covers the act in filament protecting it while troponin is not what's doing the covering of the acting filament. It's the triple mission that covers the acting filament. Troponin is just involved in moving away that trouble mission. So let's eliminate Choice A Choice B. Says it releases a teepee necessary for muscle movement. Well A. T. P. Is involved in this kind of little here on my diagram there's a molecule of ADP bound to the miocene and as part of the mice unbinding process you have a teepee, hydraulic sis and then you need a teepee again to release the medicine to relax the muscle contraction. But proponents not part of that. Troponin has the binding site for calcium as part of that process. So we're going to eliminate. Choice B. Choice C. Says that adjusts the pressure on the muscle. Well that's not Troponin that's the mason that's causing the muscle contraction. So Choice C. We're going to eliminate. So we've just got Choice D. Left says it interacts with the calcium ions to expose the myosin binding sites on the act and filament. And that is indeed correct. That is what Troponin does interacting with calcium to get triple missin out of the way. So Choice D. Is our correct answer. Thanks for watching. See you in the next video

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Key Concepts

Calcium Ions in Muscle Contraction

Troponin and Tropomyosin

T Tubules and Action Potentials