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Difference Between Actin and Myosin

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Each type of muscle tissue contains the proteins myosin and actin. Muscle contractions and movement are caused by the interaction of thick myosin filaments and thin actin filaments. The molecular motor known as myosin transforms the chemical energy supplied by ATP into mechanical energy. The actin filaments are subsequently pulled along by this mechanical energy, contracting the muscle fibers and resulting in movement.

Actin and myosin, coupled with the regulatory proteins known as troponin, tropomyosin, and meromyosin, control voluntary muscle movements within the body. Myofibrils, which are longitudinally structured filaments, are created by the actin and myosin proteins. Additionally, they are in charge of both cellular and non-cellular motions.

Actin is a protein that creates fine contractile filaments within muscle cells, which is the main distinction between actin and myosin. Myosin, on the other hand, is a protein that causes muscle cells to generate dense contractile filaments. Myosin and actin are two examples of proteins that form filaments. The muscle cells contain both of these. Actin and myosin connection and interaction also contribute to muscle contraction. In myofibrils, they are organized longitudinally.

What is Actin?

Actin is the name given to a group of protein molecules that bind together in muscle cells to form a thin band. In eukaryotes, the protein filament is in charge of forming the cellular cytoskeleton. It is further separated into monomeric and polymeric forms, known respectively as G-actin and F-actin. While F-actin is a filamentous actin protein, G-actin is a globular actin protein. These bands are essential for processes like cell migration, cytokinesis, and muscle contraction. Additionally, they support movement, communication, and maintaining the cell’s form.

What is Myosin?

The term “myosin” refers to a family of proteins that assemble into dense bands in muscle cells. When calcium ions are present, these protein filaments function and help to produce a force that helps in muscle contraction. Myosin has a head, neck, tail, heavy chains, and light chains as part of its structure. 

Myosin has a spherical, actin, and ATP-binding site-filled head. A binding site for various molecules is located in the tail and in neck region, respectively. The sliding filament theory provides a better explanation of how muscles contract. When the actin thin filament glides past the myosin thick filament, tension is created in the muscle.

Similarities between Actin and Myosin

  • The muscle contains both the protein components myosin and actin.
  • These are types of motor proteins used for muscle contraction and motion of the entire body.
  • Both of them produce contractile filaments, where filaments produced by actin are thin and short and filaments produced by myosin are thick and long. 
  • The interaction between actin and myosin is necessary for the generation of cellular growth and movement. 
  • In order to produce the mechanism for muscle contraction, actin and myosin bind together. This creates cross bridges that move filaments.

Working of Actin and Myosin

Muscle contractions brought on by actin and myosin together result in movement. An electrical signal is first sent from the brain to the muscle cell by a motor neuron. Acetylcholine, a neurotransmitter, is released as a result. In reaction to acetylcholine, the sarcoplasmic reticulum releases calcium ions. The protein known as troponin is then bound by the calcium ions. Troponin is a protein found in muscle tissue that is sandwiched between actin filaments and is related to a different protein called tropomyosin.

Upon binding with calcium ions, troponin undergoes a structural shift. This ‘unblocks’ the myosin-binding sites on the actin filament by removing tropomyosin from them and allowing the myosin heads to attach to the filament. The myosin heads can bind to the exposed binding sites on the actin filaments once tropomyosin has moved out of the way. As a result, actin-myosin cross-bridges are formed, starting the process of muscle contraction. The myosin acts as a motor to transform the chemical energy released by an ATP hydrolysis reaction into mechanical energy. This mechanical energy is used by the myosin to drive its head groups into the center of the sarcomere. The actin filaments in the sarcomere are drawn towards the center by this motion, shortening and contracting the sarcomere. Muscle movement is produced by the muscle fiber contracting as a result of the sarcomere contracting. 

Difference

Actin

Myosin

Function

The majority of eukaryotic cells include actin, a group of globular proteins that contributes to the body’s structure, form, and motion.

The motor proteins known as myosin are the building blocks of muscle fiber contraction.

Produced by

Troponin, tropomyosin, and actin proteins make up the filaments.

Meromyosin and myosin make up the filament.

Location

The sarcomere’s A and I bands both contain actin proteins.

Only the sarcomere A bands have myosin proteins.

Filament size

A thin and short filament is formed by actin

A thick and long filament is formed by myosin

Filament Quantity

The quantity of actin filaments is huge.

There are six actin filaments for every myosin filament.

Surface

The actin’s surface is smooth.

The myosin’s surface is rough.

Ends

In actin, both ends are attached to the Z-line, with one end being free.

In myosin, both ends are free.

Sliding

When the muscle contracts, actins slide into the H-zone.

Myosin remains stable during contraction, with no sliding

FAQs on Actin and Myosin

Question 1: What are actin and myosin?

Answer:

All the muscular tissue contain the proteins myosin and actin. Actin produces smaller, thinner filaments (7nm in diameter) than myosin, myosin has a filament diameter of 15 nm . Together, actin and myosin filaments produce force. This force causes the muscle cells to contract, which helps the muscles and subsequently the bodily structures to move.

Question 2: Explain the working of actin and myosin.

Answer:

Together, actin and myosin cause muscular contractions, which lead to movement. A motor neuron transmits an electrical signal from the brain to the muscle cell first. This causes the neurotransmitter acetylcholine to be released. The sarcoplasmic reticulum releases calcium ions in response to acetylcholine. The calcium ions then attach to a protein known as troponin. Muscle tissue contains troponin, which is sandwiched between the actin filaments and is connected to another protein called tropomyosin.

Question 3: What is the importance of myosin in the body?

Answer:

Myosin, is a protein that transforms chemical energy in the form of ATP into mechanical energy to produce force and movement. Muscle contraction is the most prominent example of such movement, and it serves as a model for studying actin-myosin interactions and the motor activity of myosin molecules.

Question 4: How are actin and myosin formed?

Answer:

Myosin, the most prevalent protein in muscle, is made up of thick filaments that alternate and interdigitate with two long strands of bead-like actin molecules to form a thin filament in muscle. Actin and myosin are activated when a signal for muscular contraction travels via a neuron to a muscle cell.

Question 5: How are actin and myosin involved in muscle contraction?

Answer:

Actin and myosin filament interaction, which causes their movement in relation to one another, causes muscle contraction. Myosin’s association with actin filaments, which enables it to operate as a motor to promote filament sliding, provides the chemical basis for this relationship.



Last Updated : 27 Feb, 2023
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