How does the cross arm formed in meromyosin?
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Answer:
Meromyosin is a part of myosin (mero meaning "part of"). With regards to human anatomy myosin and actin constitute the basic functional unit of a muscle fiber, called sarcomere, playing a role in muscle contraction.
Biochemically viewed meromyosin form subunits of the actin-associated motor protein, myosin, which is formed by trypsin proteolysis (protein breakdown).[citation needed] Following proteolysis, two types of meromyosin are formed: heavy meromyosin (HMM) and light meromyosin (LMM).
Light meromyosin has a long, straight portion in the “tail” region. Heavy meromyosin is a protein chain terminating in a globular head portion/cross bridge. HMM consists of two subunits, Heavy Meromyosin Subunit 1 and 2 (HMMS-1 and HMMS-2). The majority of myosin activity is concentrated in HMMS-1. HMMS-1 has an actin binding site and ATP binding site (myosin ATPase) that determines the rate of muscle contraction when muscle is stretched.
Light and heavy meromyosin are subunits of myosin filaments (thick myofilaments).
Myosin is a polymerised protein, i.e., polymer of meromyosins
Meromyosin has two parts: Globular head with a short arm (Heavy meromyosin; HMM) and a tail (Light meromyosin; LMM)
The head and the arm project outwards at a regular distance and angle from each other at the surface of the polymerised myosin and are together called the cross arm.