Question

A student simulates muscle contraction in a model using the following order of events:

Calcium pumps of the sarcoplasmic reticulum open.
Tropomyosin moves.
Calcium ions bind to troponin.
Myosin heads bend to attach to actin filaments.
Based on the order of steps in the student's model, will the muscle successfully contract?
Yes, the muscle model will successfully contract because the sequence is correct
No, because tropomyosin cannot move before the myosin heads attach to actin
>>>>No, because tropomyosin cannot move before calcium ions bind to troponin
No, because the calcium pumps

Answer 1

@AloneS is this right ?

Answer 2

i think it's right because you need to switch 2 and 3. Tropomyosin sits outside of the actin which blocks the binding sites (where the myosin head will bind), so the calcium ions need to bind to troponin (number 3), which will cause the tropomyosin to move (number 2).

Answer 3

I'm confused, how many choices are there x.x

Answer 4

1) Yes, the muscle model will successfully contract because the sequence is correct
2) No, because tropomyosin cannot move before the myosin heads attach to actin
3) No, because tropomyosin cannot move before calcium ions bind to troponin
4) No, because the calcium pumps cannot open before the tropomyosin moves

Answer 5

well i'm going to go with C

Answer 6

@mathmate

Answer 7

I agree that the order is not correct. But I believe that the attractive forces between myosin and actin are \(initiated\) by the Ca++ ions. The two then slide alongside each other, which is the contractile process. The attachment should be step 2.
(ref. Guyton & Hall)

Answer 8

based on what you just said i would say 4 , is the best choice.

Answer 9

If calcium ions are not present, then there is no attraction between myosin and actin. Do you then agree that tropomyosin cannot move before calcium pump opens?

Answer 10

yes i do , the correct order should be
Calcium pumps of the sarcoplasmic reticulum open.
Myosin heads bend to attach to actin filaments.
Calcium ions bind to troponin.
Tropomyosin moves.

Answer 11

I agree with the above, but please check with your textbook to double-check.

Answer 12

@word2
perhaps this could help too!
https://www.khanacademy.org/science/health-and-medicine/human-anatomy-and-physiology/introduction-to-muscles/v/tropomyosin-and-troponin-and-their-role-in-regulating-muscle-contraction