MICROANATOMY

Detailed explanation-1: -Tropomyosin blocks myosin binding sites on actin molecules, preventing cross-bridge formation and preventing contraction in a muscle without nervous input. Troponin binds to tropomyosin and helps to position it on the actin molecule; it also binds calcium ions.

Detailed explanation-2: -1 Tropomyosin. TM regulates smooth muscle contraction by blocking the myosin binding sites on actin, preventing actin–myosin interaction.

Detailed explanation-3: -Actin Associated Proteins. Tropomyosin (TM), a long fibrous protein lies along the long pitch double-helical thin filament spanning seven actin monomers and through end-to-end contacts continuously covers the actin filament in all muscles.

Detailed explanation-4: -This can only happen in the presence of calcium, which is kept at extremely low concentrations in the sarcoplasm. If present, calcium ions bind to troponin, causing conformational changes in troponin that allow tropomyosin to move away from the myosin binding sites on actin.

Detailed explanation-5: -Tropomyosin binds to troponin to form a troponin-tropomyosin complex. The troponin-tropomyosin complex prevents the myosin “heads” from binding to the active sites on the actin microfilaments. Troponin also has a binding site for Ca++ ions.