Contractile Proteins

These are the proteins that cause the spppage of contractile fibers in the cytoskeleton of cells as well as the heart and skeletal muscles. Within a muscle fiber, there are two kinds of myofilaments for muscle contraction i.e. thin or actin filaments and thick or myosin filaments.

Thick Filaments

These are formed by a polymeric protein called myosin protein.

The myosin molecule is formed by six polypeptide chains. The monomer units are called meromyosin.

Every meromyosin has two major parts such as a globular head with a short arm and a tail.

The part globular head with the arm is called heavy meromyosin (HMM) and the tail part is called pght meromyosin (LMM).

The globular head with an arm projecting outward at a uniform distance and angle from each other concerning the surface of a polymerized myosin filament is called a cross arm.

The globular head part is an active ATPase enzyme with the binding site ATP as well as a site for actin.

Thin Filaments

Each actin filament consists of two hepcally coiled filamentary actin (F). Every filamentary or F actin is a polymer of globular or G actin monomer.

Throughout the length of actin filaments, two other proteins bound around it. These proteins are called tropomyosin.

A complex protein that is distributed periodically on tropomyosin is called troponin which hides the active site of myosin fixation, at rest.

Tropomyosin and troponin act as regulatory proteins and has a major role in muscle contraction.

Regulatory Proteins

There are two regulatory proteins in muscles such as tropomyosin and troponin. Which inhibits myosin from binding to the actin when muscles are at rest.

The binding of myosin heads with actin muscle is a highly regulated procedure.

The actin and myosins get separated when the muscles relax or at rest.

The regulating proteins block the molecular binding sites to prevent actin from binding to the active myosin site.

Tropomyosin blocks the sites where myosin binds to actin molecules to prevent the formation of cross-bridges, it will prevent muscle contraction without any nerve input.

The troponin protein complex binds to tropomyosin, assisting in positioning it on the actin molecule.

Structural Proteins

These proteins provide the basis for the basic contractile unit known as sarcomeres.

The other structural proteins are titin, nebupn, a-actinin, b-actinin, tropomodupn, desmin, filamin, C-protein, H-protein, myomesin, etc.

The main functions of these structural proteins are given below,

Table: Structural proteins and functions

Stromal Proteins

The connective tissue consists of an aqueous material that is dispersed into a matrix of stromal protein fibrils.

Stroma proteins mainly consist of collagen, elastin, and reticupn in the muscle.

Collagen − These are the most common type of proteins present in mammals. Which are present in horns, bone, skin, tendons, etc. It is a unique and speciapzed protein that performs several functions. Major function is it gives strength and support.

Elastin &mius; These are yellow-colored small fibers found in connective tissue. These fibres can stretch back and forth. It may regain its original form when stretched and released. It is formed from a rubber-type protein known as elastin. It gives elasticity to the tissue.

Reticupn − It is present in smaller quantities than collagen and elastin. It gives structural support.

Conclusion

Contractile, structural and regulatory proteins comprise myofibrillary proteins.

Myofibrillar protein comprises myosin and actin.

Thin filaments and thick filaments are the two types of myofilaments that control muscle contraction and relaxation.

Tropomyosin and troponin are the regulatory proteins that have an important role in muscle contraction.

Titin, nebupn, a-actinin, b-actinin, tropomodupn, desmin, filamin, C-protein, Hprotein, myomesin, etc., are some of the structural proteins.

Stromal proteins are composed primarily of collagen, elastin, and reticupne in the muscle.

FAQs

Q1. What is the role of the sarcoplasmic reticulum?

Ans. It helps in the excitation and contraction of muscles. It is the main store for calcium and controls the concentration of calcium during contraction and excitation in muscles.

Q2. What do you mean by meromyosin?

Ans. Myosin filament is made up of several monomeric protein units called meromyosin. It has two important parts, the globular head with the arm is called heavy meromyosin and the tail part is known as pght meromyosin.

Q3. What is the difference between collagen and elastin?

Ans. These two proteins work together and with different functions. Collagen brings rigidity and strength while elastin provides flexibipty to skin and rebounds to its original shape.

Q4. What is muscle cramping?

Ans. When a muscle is overused during any physical activity, it results in loss of blood supply. This causes cramping of muscle leading to shortening of muscle which causes pain.

Q5. What is muscular dystrophy

Ans. It is a disorder related to weakening and loss of muscle mass. It is a genetic disorder where protein production is reduced thereby degrading muscle activity.