Answering the question, the association between tropomyosin and troponin molecules in resting striated muscle fibers is such that troponin holds the tropomyosin in place on the actin.
The actin protein is the main part of thin filament but there are two other components which are tropomyosin and troponin.
However, the actin protein consists of binding sites that can hold myosin, that is, the actin has binding sites that where myosin can be attached. When the muscles are at rest, the Tropomyocin blocks the interactions between actin and myosin which prevent the cross-bridging formation as well as a contraction in muscles.
However, the troponin is made up of three globular subunits. One of the subunits connects with tropomyosin while the other two binds with actin and ca 2+ ions respectively.
Also, to allow a muscle contraction, there must a change in the way the tropomyosin reacts, the change of formation is necessary to enable cross bridge-formation.
Muscle contractions also required the presence of calcium and it must also be at a very low concentration within the sarcoplasm.
The presence of calcium would make it possible for calcium ions to joins with tropomyosin and muscle contraction can then take place.
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