Question: 100% NCERT covered from Particular Keyword.Explanations are 100% from NCERT | [Difficult level: Easy] From NCERT NEET Derived Question.
Which of the following is the contractile protein of a muscle?
(a) Myosin (b) Tropomyosin
(c) Actin (d) Tubulin
Answer:
Myosin
👉A characteristic feature of the muscle fibre is the presence of a large number
of parallelly arranged filaments in the sarcoplasm called myofilaments or
myofibrils. Each myofibril has alternate dark and light bands on it. A
detailed study of the myofibril has established that the striated appearance
is due to the distribution pattern of two important proteins – Actin and
Myosin.
👉The light bands contain actin and is called I-band or Isotropic
band, whereas the dark band called ‘A’ or Anisotropic band contains
myosin.
👉Both the proteins are arranged as rod-like structures, parallel to
each other and also to the longitudinal axis of the myofibrils. Actin
filaments are thinner as compared to the myosin filaments
👉In the
resting state a subunit of troponin masks the active binding sites for
myosin on the actin filaments
👉Each myosin (thick) filament is also a polymerised protein. Many
monomeric proteins called Meromyosins constitute one
thick filament. Each meromyosin has two important parts, a globular
head with a short arm and a tail, the former being called the heavy
meromyosin (HMM) and the latter, the light meromyosin (LMM). The HMM
component, i.e.; the head and short arm projects outwards at regular
distance and angle from each other from the surface of a polymerised myosin
filament and is known as cross arm. The globular head is an active ATPase
enzyme and has binding sites for ATP and active sites for actin.