Question

The given figure shows an action (thin) filament. Identify the labeled parts A, B, and C and select the correct option.

(a) A – Tropomyosin, B – Troponin, C – F-actin
(b) A – Troponin, B – Myosin, C – Tropomyosin
(c) A – Troponin, B – Tropomyosin, C – Myosin
(d) A – Troponin, B – Tropomyosin, C – F-actin

Answer 1

Hint: They are composed of protein molecules out of which one is a coiled protein, the other is composed of regulatory proteins that are present in different tissues while the third one is a globular protein.

Complete step by step answer:
The given figure is of actin filament which is thin and is composed of tropomyosin, troponin, and F- actin. Tropomyosin is made of alpha-helical coiled proteins whose function is to constitute cell cytoskeletons. Troponin is composed of various regulatory proteins in cardiac and skeletal muscles that help in muscle contraction. F-actin is a globular protein that helps in the formation of microfilaments.
- The actin and myosin are the types of filaments of myofibrils which are called myofibrils.
- On the basis of the arrangement of the myofibrils, tissues are of various types including cardiac muscles, and skeletal muscles (striated muscles) , and smooth muscles.
- Tropomyosin is the constituents of actin filament that helps in the regulation of actin filaments of both muscular and non- muscular cells.
- They are responsible for the functioning of the cytoskeleton formation and regulating muscle contraction.
- The Troponin level in blood may be measured by a person to diagnose the marker for the stroke.
- They may act as a blockage for the contraction of muscle as they attach in the place of actin filaments.
- Actin is a filament of myofibrils that is composed of various multi-functional proteins.
- Actin filaments are of two types G- actin (Globular actin which is a free monomer) and F- actin (Filamentous actin having a long chain of polymer) .
- They help in the transport of various nutrients and help the cell to contract during cell division.
So, the correct answer is ‘(a) A – Tropomyosin, B – Troponin, C – F-actin’.

Note: In 1887 W. D. Halliburton was the first to observe action through his experiment. It has been found to be the most conserved protein even after evolution. In 1942 the F-actin was discovered by Straub. Its structure was found by Holmes through X0ray crystallography in 1990. Tropomyosin was first discovered in 1946 and isolated in 1948 by Bailey. Troponin was first discovered at the University of Heidelberg by the German physician Hugo A. Katus.