The formation of a thin actin filament is shown in figure 1. Figure 1: Formation of a Thin Actin Filament. Though the polymerization of actin filaments starts from both ends of the filament, the rate of the polymerization in each end is not equal. This results in an intrinsic polarity in the filament. The association of the tropomyosin and troponin stabilizes the actin filament. The subdomains of the G-actin is shown in figure 2. Figure 2: G-Actin Subdomains. The shape and movement of the cell depend on the actin filaments.
The main function of actin filaments is to form the dynamic cytoskeleton of a cell. The cytoskeleton gives structural support and links cell interior to its surroundings. Actin filaments are also involved in the formation of filopodia and Lamellipodia that aid the cell motility. Actin filaments aid in the transport of organelles to the daughter cells during mitosis. The complex of thin filaments in muscle cells generates forces, supporting the contraction of the muscles.
Myosin refers to a protein that forms the thick contractile filaments in muscle cells. All myosin molecules are composed of one or two heavy chains and several light chains. Three domains can be identified in this protein: head, neck, and tail. The head domain is globular and contains actin and ATP binding sites. The tail site contains the binding sites for different molecules. The structure of the myosin is shown in figure 3. The myosin I is involved in the transport of vesicles.
The myosin II is responsible for the muscle contraction. The structure of a skeletal muscle is shown in figure 4. Figure 4: Skeletal Muscle Structure. Myosin forms a long filament of 4. Myosin contains meromyosin protein.
Found in Actin is present in A and I bands. Myosin is present in A bands of the sarcomere. Cross bridges Actin does not form cross-bridges. Myosin form cross-bridges. Surface The surface of actin is smooth. The surface of the myosin is rough. Number Actin is numerous in numbers. Myosin is less in number, and they are one per six actin filaments.
Slide into Actin slide in H zone at the time contraction. Myosin does not slide at the time of contraction. As discussed above, the two primary protein filaments found in muscles are actin and myosin. It is one of the essential components of the cellular cytoskeleton, especially in eukaryotes. It is a highly conserved protein having the molecular weight of 42kDa. These have different cellular functions like muscles contraction, cytokinesis and cell migration. As actin filaments play a primary role in the formation of the dynamic cytoskeleton of the cell, hence it provides the movement and shape also to the cell.
The cytoskeleton also delivers communications with the neighbouring cells, also supports the interior surrounding within the cell. Myosin is another type of protein filaments that works in the presence of calcium ions. Myosin is known to generate the force that is required during muscle contraction.
So, it is also known as motor protein. Cross bridges. Myosin forms cross-bridges. Proteins in filament. Actin protein. Tropomyosin protein. Troponin protein. Myosin protein Meromyosin proteins. Association with ATP. Not associated with ATP molecules. Remains associated with ATP molecules. Actin filaments slide into the H zone during contraction. Myosin filaments do not slide into the H zone during contraction.
Actin is present in muscle fibres, microfilaments, cell membrane, and cell wall. Myosin is primarily found in muscle cells. Muscle Contraction. Actin interacts with myosin to support muscle contraction.
Myosin initiates muscle contraction by generating a force by binding to the ATP molecule. As a result, it is said that myosin and actin collaborate during muscle contractions, with myosin serving as the precursor protein in the conversion of chemical energy ATP to mechanical energy. So, apart from muscle contraction, actin and myosin play an important role in cell biology by engaging in cell division , nonmuscle cell functions, and so on.
Myosin is smoother and has deeper striations than actin. The sliding filament theory can explain how muscle contractions function. Basis of Comparison Actin Myosin Meaning The proteins that form the thin bands in myofibrils are known as actin.
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