Difference Between Actin and Myosin

Muscles are made up of protein. Actin and myosin are two protein molecules in muscles that are primarily responsible for muscle contraction in humans and animals.

Both actin and myosin function by controlling voluntary muscle movement within the body, along with regulatory proteins known as troponin, tropomyosin, and meromyosin, actin and myosin proteins form filaments that are arranged lengthwise into myofibrils. they are also responsible for cell movements and decellularization.

difference between actin and myosin types

The main difference between actin and myosin is that actin is a protein that forms a thin connective tissue inside muscle cells. In contrast, myosin is a protein that forms dense contractile filaments in muscle cells.

Difference Between Actin and Myosin



Size of the Filament

Forms a thin and short filament. Myosin forms a thick and long filament.

Regulatory Proteins

It consists of tropomyosin and troponin. It consists of meromyosin.


Found in A and I bands. Found in A bands of a sarcomere.

Cross Bridges

Do not form cross-bridges. Form cross bridges.


The actin filaments have a smooth surface. The myosin filaments have a rough surface.


Actin filaments are huge in number. One myosin filament happens per six actin filaments.


Actin filaments have lighter striations. Myosin filaments have dark striations.


Slide into the H-zone during contraction. Do not slide during contraction.


Actin filaments are free at one end. Myosin filaments are free at both ends.

Types of Actin and Myosin

  • The MLC20 is also known as the regulatory light chain and actively participates in muscle contraction.
  • The MLC17 is also known as the essential light chain. Its exact function is unclear, but is believed to contribute to the structural stability of the myosin head along with MLC20.

Some myosins have a single heavy chain and interact with actin filaments at only one site, other myosin isoforms have two heavy chains and interact with actin filaments at both sites.

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