In muscle cells, myosin molecules continue moving along actin molecules as long as:
a. ATP is present and troponin is not bound to Ca²⁺.
b. ADP is present and tropomyosin is released from intracellular stores.
c. ADP is present and the intracellular acetylcholine level is high.
d. ATP is present and the intracellular Ca²⁺ concentration is high.

Question

In muscle cells, myosin molecules continue moving along actin molecules as long as:

a. ATP is present and troponin is not bound to Ca²⁺.

b. ADP is present and tropomyosin is released from intracellular stores.

c. ADP is present and the intracellular acetylcholine level is high.

d. ATP is present and the intracellular Ca²⁺ concentration is high.

Accepted Answer

Hi, everyone. Let's look at our next question. It says which of the following must take place in order to expose the M and binding site. Well, we're talking about the mycin binding site on the acting filament. Let's recall that the troy and protein blocks that binding site and needs to be moved out of the way. So I'm just going to have a little diagram. So we can think about that process or a big diagram. Let's shrink that a bit. So here we have our acting filament and it's blocked by the troy protein. Here, here's the min uh prevented from blocking. In order to expose the site and allow the my to bind and form that cross bridge. For muscle contraction, we have to have a molecule of CAL molecule. An I A calcium ion come in and bind the site on the protein troponin. Once the calcium is bound that causes the troponin to move the trom mycin out of the way, exposing that binding site on acting. So in order to expose the mic and binding site, a calcium ion must bind a troponin. So let's look at our answer choices and find that and we can see that choice D is troponin must bind with calcium to move troo mycin. So that's our answer. Let's just walk through the other choices. Choices A says Troy must be securely wrapped around, acting well, when Trobicin is wrapped around the act in the binding site is blocked. So that's not a correct answer. We're looking at what exposes that site choice B says there should be a sufficient supply of A TP. Well, A TP is the yellow molecule up here. A TP is needed to allow the min to um bind to move down and bind with the act. And then you need another molecule of A TP to come in and bind and allow the mycin to release. So A TP is necessary for the min to bind and release, but it's not involved in unblocking the mycin binding site. It's calcium that we need to cause the troy to move out of the way. So choice B is not our answer. Choy C says A TP must be hydrolyzed to provide energy. Again, that's necessary for my A TP comes in and binds here gets hydrolyzed. That will allow the mycin to move down once the active site is exposed and then A TP gets hydroly again when it binds to the myo allowing it to release. But that's not part of the troy process here. So not our correct answer. So again, which must take place in order to expose the Mycin binding site. That's choice C troponin must bind with C A two plus to move trip Mycin. See you in the next video.

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Key Concepts

ATP and Muscle Contraction

Role of Calcium Ions (Ca2+) in Muscle Contraction

Troponin and Tropomyosin Regulation