Difference Between Actin and Myosin

Our bodily motions are fully dependent on our muscle cells. Three types of muscles are present in our vertebrates for smooth effortless motions and movements.


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For any voluntary movement, contractile filaments in our muscle cells need to get built and proteins like actin and myosin help in this formation.

Actin vs Myosin

The difference between actin and myosin is that actin forms thin contractile filaments and myosin forms thick contractile filaments in the muscle cells. Actin has one free end and on the other hand, myosin exists with both free ends. Again, the cross-bridge does not get formed by actin but myosin does it.

Actin vs Myosin 1

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Actin is a type of globular protein that is liable to construct contractile filaments for our muscles which will lead to uninterrupted movements of the body.

The contractile filaments made by actin are thin and the surface of it is smooth. It is constructed by troponin and tropomyosin.

Myosin is a motor protein that is in charge of making thick contractile filaments. Myosin is a large part and it can be divided into three parts further based on their functions.

The surface of myosin is rough and it also takes up energy from ATP to generate force to accomplish different movements.

Comparison Table

Parameters of ComparisonActinMyosin
Definition Actin is a protein that is responsible to form thin contractile filaments in muscle cells.Myosin is the protein that is responsible to form thick contractile filaments in muscle cells.
SurfaceIt has a smooth surface.It has a rough surface.
Free endOne end of it is free.Both ends of it are free.
Made ofIt is made of troponin and tropomyosin.It is made of meromyosin.
Situated at It is situated in the A and I bands of sarcomere protein.It is situated in A band of sarcomere protein.
ATPActin does not need any assistance from ATP.Myosin takes help from ATP to fulfil its functions.

What is Actin?

Actin falls under the group of globular proteins that are present in a major amount in the cells of our body for our mobility purpose. The protein called actin is responsible to form a thin contractile filament.

Our body has various cells and one of them is eukaryotic cells in which actin protein stays in abundant amounts.

Actin is preserved protein. And has two forms, one is G-actin or monomeric and the other is F-actin or filamentous. Under a few certain physiological conditions, the G-actin can create F-actin. And in this making, G-actin takes up energy.

Our cells move and get their shape from the actin filaments. The main function of actin is to build the cytoskeleton of a cell which offers structural support to the other cells that surround it.

Actin also forms other elements that get involved in the support system of our cells, such as filopodia and Lamellipodia.

What is Myosin?

Myosin is a protein that is responsible to form contractile filaments in our muscle cells and these are very thick when they are formed by myosin. Myosin forms cross bridges, its molecules are designed in chain forms.

It belongs to the motor protein family.

Myosin is accountable to execute actin-based motility and to do so, they depend on the ATP. Myosin is restricted to muscle cells and can not be regarded as a single cell but as a large superfamily of genes.

The protein products of myosin carry a lot of properties that are a lot similar to the properties of actin.

The whole structure of myosin molecules can be divided into three parts, head, neck and tail. The Head assist the walk and also ties the available filamentous actin. Neck mostly has regulatory functions to perform.

And the tail is mostly connected with the regulation of motor activities.

Main Differences Between Actin and Myosin

  1. Actin is a type of protein that is responsible to form thin contractile filaments in the muscle cells of the body but myosin is the protein that is responsible to form thick contractile filaments in muscle cells.
  2. The surface of actin is smooth but on the contrary, the surface of myosin is rough.
  3. Actin is known to be a globular protein whereas myosin is part of motor proteins.
  4. Actin has no connection with ATP molecules but myosin is associated with it.
  5. The molecule weight of actin is less than the molecules of myosin.
  6. The amount of actin is found in abundance but myosin is not that abundant in its amount.
  7. One end of actin remains free but in the case of myosin, both its ends are free.
  8. Both actin and myosin can be found in sarcomere protein, however, A and I bands of sarcomere protein give place to actin but myosin is only situated in the A band.
  9. Actin is not capable of forming cross-bridges but myosin can form it.
  1. https://www.pnas.org/content/72/3/994.short
  2. https://www.tandfonline.com/doi/pdf/10.3109/10409237409105443
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