Question

Which of the following is not involved in muscular contraction?
A. Calcium ion
B. Troponin
C. Actin
D. Magnesium ion

Answer 1

Hint: The mechanism of muscle contraction is explained by a theory called Sliding filament theory. According to this theory, the contraction of muscle fibre occurs when thin filament (Actin filament) slides over thick filament (Myosin filament).

Complete answer:
Calcium ion plays an important role in muscle contraction by developing the interactions between the proteins, myosin and Actin. The \[C{a^{2 + }}\ ions bind to the Actin filament, which exposes the binding site for the myosin head to bind to stimulate a muscle contraction.
Troponin: Troponin is a trimeric protein. Troponin is attached to the protein tropomyosin and lies in the grooves between Actin filaments in muscle tissue. When the muscle cell is stimulated to contract, calcium channels open in the sarcoplasmic membrane and release calcium into the sarcoplasm. Some amount of calcium attaches to troponin. Troponin masks the active binding sites for myosin on Actin filament.
Troponin 1: It inhibits Actin-myosin interaction.
Troponin T: It is the binding site for tropomyosin.
Troponin C: It is the binding site for calcium.
Actin: Actin is a globular protein, which has a low molecular weight. It occurs in two forms:
Monomeric G-Actin
Polymeric F-Actin
Actin participates in many cellular processes such as muscle contraction, cell motility, cell division and cytokinesis.
Magnesium ion: Magnesium ion helps in the relaxation of muscles, it acts as a natural calcium blocker to help muscle relax.

So the correct answer in option D.

Note: The thick myofilament is made up of myosin and the thin myofilament is made up of Actin. The thin myofilament has three proteins: Actin, tropomyosin and troponin.