10 Differences between Actin and Myosin with Similarities

What are the differences between actin and myosin?

Skeletal muscle comprises protein filaments. Actin and myosin are some of the common popular protein filaments found in the muscles. They are responsible for the muscular movement of the body.

The discussion provides a detailed insight into the difference between actin and myosin in tabular form to facilitate easier understanding. You will also be able to write the difference between red and white muscles in the long run.

Differences between Actin and Myosin

What Is Actin?

Actin refers to a collection of protein molecules that form a thin band in muscle cells. The protein filament is responsible for the development of the cellular cytoskeleton in eukaryotes. It is further subdivided into monomeric form as G-actin and polymeric form as F actin.

The G-actin represents globular actin protein while F-actin represents filamentous actin protein. These bands play a vital role such as muscle contraction, cytokinesis, and cell migration. Besides that, they help in communication, movement, and maintaining the shape of the cell.

What Is Myosin?

Myosin refers to the group of proteins that form thick bands in the muscle cells. These protein filaments work in the presence of calcium ions and it helps to generate force that facilitates muscle contraction.

The structure of myosin comprises light chains, heavy chains, head, neck, and tail. The head of myosin is globular which contains actin and ATP binding sites. The neck region contains α-helical and the tail contains a binding site for different molecules.

The sliding filament theory help to describe the contraction of muscles. The generation of tension in the muscle occurs when the thin filament of actin slides over the thick filament of myosin.

Comparison Chart: Actin Vs Myosin

Basic Terms Actin Myosin
Meaning These are protein molecules that form a thin contractile filament in muscle cells These are a group of proteins that form a thick contractile filament in muscle cells
Size of the Filament Thin (0.005 μm)

Short (2 – 2.6 μm) filament

Thick (0.01 μm)

Long (4.5 μm) filament.

Regulatory Proteins Contain tropomyosin and troponin. Comprise of meromyosin
Location A and I bands A band of a sarcomere
Cross Bridges Absent Present
Surface Smooth Rough
Number Great in numbers One myosin filament occurs per six actin filaments.
Ends Free at one end Free at both ends
Sliding Slide into the H zone during contraction. Do not slide during contraction

Core Differences between Actin and Myosin

  1. Actin filaments are found in A and I –bands while myosin filament in the A-band of sarcomere only
  2. Myosin filament is thicker and longer while actin filament is thinner and shorter
  3. Myosin filament has a cross-bridge while actin filament has no cross bridge
  4. The surface of an actin filament is smooth while that of myosin filament is rough
  5. Actin filaments tend to be great in numbers while myosin filaments are fewer
  6. The ends of myosin filaments are free at both ends while actin filaments are free at one end
  7. Actin filament tend to slide into the H zone during a contraction while myosin does not slide during contraction
  8. Actin filament comprises actin, tropomyosin, and troponin while myosin filament consists of myosin and meromysin

Core Similarities between Actin and Myosin

  1. Both are protein molecules in the muscles
  2. Both are the type of motor proteins
  3. Both form contractile filaments
  4. Both are involved in muscle contraction
  5. Both require muscle contraction

Comparison Video


The core difference between actin and myosin is that actin form thin filament whereas myosin form thick filaments. These terms can help you understand more about the difference between A and I bands.

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