Differences Between Actin and Myosin – Actin vs Myosin


Table of Contents

What is Actin?

Actin is one of the globular proteins. They’re among the top proteins within the majority of eukaryotic cells. They assist in providing structure, shape and flexibility to the body.

Actin is found in all eukaryotes with the exception of the nematode Sperm. Actin proteins are extremely conserved and play a role in the most protein-protein interactions of any other protein known. Actin differs from other proteins due to the ability to switch between two states: Monomeric (G-actin) or filamentous (F-actin) state. The process is through the control of nucleotide hydrolysis, ions as well as a number of actingin-binding proteins.


Actin is the unimeric component of two filaments in the cytoskeleton; microfilaments as well as contractile apparatus. Actin proteins play an essential role for cell differentiation, motility as well as cell-mediated signaling. Cells’ capacity to form a dense microfilaments network allows cells to alter themselves as it responds to environmental factors such as increasing adhesion of cells to create tissues. Vertebrates produce three actin isoforms, which include three a-isoforms that are associated with cardiac, skeletal and smooth muscles. the b-and g-isoforms are found in nonmuscle and muscle cells.

The actin filaments of muscles are small in size, between 2-2.6 um, and are thin with a an average diameter of 0.005 millimeters. The filaments of actin in the muscles are separated by actin-binding proteins. the a-actinin protein that connects two actin filaments, and leaves room for myosin. The a-actin protein is the main part of the muscles’ contractile apparatus. Every actin filament of the muscle fiber is made of two actin strands.


Examples of Actin


Microfilaments within cells Also known as actin filaments are proteins that are element of the cell’s cytoskeleton. They are polymers of actin proteins that are able to interact with other proteins within the cell. Microfilaments measure about 7 millimeters in diameter and each filament comprises two actin strands. Microfilaments serve a range of roles including cytokinesis, transforming the cell’s shape to cell mobility. Furthermore, the actin structures are also found close of the plasma membrane, creating an organelle that changes in accordance with the purpose of the cell. It’s like the middle part of mammalian Sperm.

What is Myosin?

Myosin is one of the superfamily of motor proteins. They along and actin protein, constitute the foundation for the contraction of muscle fibers.


Myosin is referred to as motor protein because it is an enzyme that transforms the energy of chemical reactions into energy that can be used in mechanical ways. Myosin is an ATPase which is able to move along filaments of actin by linking the hydrolysis process of ATP to changes in conformation. Myosins consist of one or two chains of heavy chain as well as a number of light chains. A genomic analysis has revealed 13 distinct myosins.

Each is composed of a conserved head domain that is an ATPase activated by actin responsible for creating motion; a neck domain that is linked to many regulatory light-chain subunits the effector tail domain which is distinctive to every kind of myosin and plays a role in its particular functions in cells.


Myosin filaments are thicker in diameter, about 4 to 5 millimeters and are larger in diameter, with a diameter of 0.01 millimeters. Myosin that is found in muscle includes Myosin II that is a polymeric molecule that has a long rod-like tail domainthat is assembled into dense bipolar filaments. When in the presence of ATP the head domain dimeric of myosin II is able to generate motion.

Myosins can perform other functions than muscles contraction, based on the myosin type and the species. The nature and function of myosin are conserved across a variety of species, with the myosin found in mammals being compatible with the actin in unicellular organisms.


Examples of Myosin

Myosin in stereocilia

Myosin III proteins are located on the tips of the stereocilia within the inner ears. The stereocilia measure about 10 millimeters in size and have a similar form to the microvilli of the intestinal tract. They are mechanosensing organelles, which respond to fluid movement within the ear, and perform the function of hearing and the balancing.

It is a part of its PDZ domain-containing protein that along in conjunction with the actin proteins aids the stereocilia’s response in response to sounds. Myosin helps the stereocilia to adapt to changes in sound waves as well as fluid motion through the cilia. Additionally, genes that encode for the myosin protein are also present in other areas of the ear such as the cochlea.


Differences Between Actin and Myosin – Actin vs Myosin

Base for comparisonActinMyosin
DefinitionActin is a family of protein globules that constitute the largest amount of protein within the majority of eukaryotic cells. They aid in providing structure, shape and flexibility to the body.Myosin is a motor protein family which, along and actin protein, create the foundation for the contraction of muscle fibers.
Found inActin proteins are present in both bands of the Sarcomere.Myosin proteins are only found inside the A band of the Sarcomere.
SizeThey are smaller (2-2.6 millimeters in diameter) and also thinner (0.005 millimeters in size).They are wider (4-5 inches in total length) and more substantial (0.01 centimetres).
NatureActin proteins are globular proteins.Myosin proteins are motor protein.
Molecular weightThe molecular mass of actin proteins is considerably smaller.Molecular weight for myosin proteins is significantly greater.
The abundance of muscle cellsActin filaments are more abundant than myosin.Myosin is more scarce in comparison to actin. Myosin is the only myosin that exists for each filament of actin.
SurfaceThe actin’s surface is smooth.The myosin’s surface is rough.
Proteins in filamentsActin filaments consist of tropomyosin and actin and troponin proteins.Myosin filaments are made up of meromyosin and myosin proteins.
Bridges acrossThere are no cross-bridges in actin filaments.Myosin form cross-bridges.
Assemble with ATPActin isn’t associated with ATP molecules.Myosin is still associated with ATP molecules.
EndThe one end of the filament of actin is unbound, and the other one is bound by Z lines.The ends of both myosin filaments remain free. Myosin’s head domain is however connected to ATP.
SlidingActin filaments move through the H-zone when they contract.Myosin filaments don’t move into the H zone during contraction.
LocationActin is found in microfilaments, muscle fibers cell membrane, the cell wall.Myosin is found primarily inside muscle cells.
The contraction of muscleActin works with myosin in order to aid in the contraction of muscles.Myosin stimulates muscle contraction by producing the force through connecting to ATP molecules.

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