Question

Identify the thick myofilament from the given contractile proteins.
a. Troponin
b. Myosin
c. Tropomyosin
d. Actin

Answer 1

In cardiac and skeletal muscles of eukaryotes, myofilaments are key molecular regulators of the muscle contraction. Myofilaments are the filaments constructed from proteins principally myosins. They are ATP-dependent proteins and take part in actin-based motility.

Complete answer:
Skeletal muscle fibres are constructed from two types of filaments which are thick filament and thin filament. Each thick or myosin filament is made up of a protein known as myosin. Actin filaments are found thinner as compared to the myosin filaments. Each myosin filament is made up of many monomeric units of proteins called meromyosin.

Among the given options:

Troponins are known as a group of proteins found in skeletal and cardiac (heart) muscle fibres that control muscular contraction. Smooth muscles do not contain troponins. Three types of troponins occur namely, troponin I, troponin T, and troponin C.

Myosin is one among the three major classes of molecular motor proteins namely myosin, dynein, and kinesin. As myosin is found the most abundant of these proteins, it plays a structural and enzymatic role in muscle contraction and intracellular motility.

Tropomyosin is an actin binding protein, which consists of a coiled-dimer and forms a polymer along the length of actin by a head-to-tail overlap along the major groove of actin.

Actin is the most abundant protein found in most eukaryotic cells. It is highly conserved and takes part in more protein-protein interactions than any known protein.

Hence, the correct answer is option (B).

Note: Myofilament is the term used for the chains made of myosin proteins that pack a muscle fiber. Myosin is known as a superfamily of proteins which bind actin to hydrolyze ATP and transduce force. Thus, most are located in muscle cells.