Question

If calcium binding sites on troponin proteins were blocked by 25%, how would this impact the maximum contractile force of a muscle fibre in the context of the cross bridge cycle?

Answer 1

When Calcium binding sites on Troponin proteins were blocked by 25%,Maximum Contractile force of a muscle fibre Decreases.Maximum contractile force occur when all the muscle fibre contracts.

In Relaxed muscle,Tropomyosin masks the Myosin binding Site on actin molecule.But During Stimulus,When action potential Reach the Motor End plate,Ca2+ is Released.This ca2+ Binds to Troponin molecules.this troponin molecules are in contact with Tropomyosin molecule.Binding of Ca2+ on troponin molecule induces Change in shape of Troponin molecule so that Tropomyosin gets moved from the myosin binding sites on Actin molecule.This exposes Myosin binding sites on actin ,So that Myosin heads binds to Action------Cross bride formation --Cycle of cross bridge formation and Breakdown occur for skeletal Muscle contraction to Occur.

But when some of Ca2+ binding sites on troponin were blocked,C2+ couldnot bind in those troponin---No confirmational change in troponin-----no shift of tropomyosin from active sites on action----no cross brdige formation---hence no contraction occurs on some those muscle fibres.Hence the maximum Contractile force decreases.