Troponin and Tropomyosin

Question 1

What are tropomyosins?

Answer 1

They are coiled proteins that run along the grooves of the F-actin helix and cover the binding sites for myosin. Each tropomyosin covers around 7 G actins

Question 2

What subunits does the troponin protein complex consist of and what do each of them do?

Answer 2

3 polypeptide subunits:
TnT (binds to tropomyosin)
TnC binds to calcium ions
TnI inhibits actin and myosin interactions

Question 3

How is troponin’s control over tropomyosin regulated?

Answer 3

By the sarcoplasmic calcium ion concentration

Question 4

What happens when sarcoplasmic Ca2+ increases?

Answer 4

TnC binds 2 additional Ca2+ for a total of 4
This causes the entire troponin complex to change conformation
This in turn, draws tropomyosin from its blocking position
Contraction begins as binding sites on the G-actins are uncovered and myosin crossbridges bind