Write difference between actin and myosin

Actin and myosin are two important proteins responsible for muscle contraction and various types of cellular movement. They work together but have different structures, functions and roles in the body.

Here is the detailed comparison between actin and myosin based on different aspects:

Based on Structure and Size
  • Actin is a small and globular protein with a molecular weight of about 42 kDa. It exists in two forms: G-actin (globular actin) as a single unit and F-actin (filamentous actin) as a long chain of actin molecules. It forms thin filaments that serve as a pathway for myosin movement.

  • Myosin is a larger and more complex protein, with a molecular weight ranging from 200 to 500 kDa. It forms thick filaments and consists of a head, neck, and tail. The head region binds to actin and uses energy for movement.

Based on Function in Muscle Contraction
  • Actin serves as a support structure and provides the surface for myosin to attach and pull, which leads to muscle contraction.
  • Myosin functions as a motor protein that generates force by binding to actin and pulling it using ATP energy, causing muscle contraction.
Based on Energy Use
  • Actin binds to ATP or ADP, which helps in its polymerization into filaments but it does not hydrolyze ATP for movement.
  • Myosin contains ATPase activity, meaning it breaks down ATP to release energy, which is required for movement along actin filaments. This energy is essential for muscle contraction and intracellular transport.
Based on Role in Cells
  • Actin is a major component of the cytoskeleton, which maintains cell shape and allows movement. It plays a role in cell division, endocytosis and intracellular transport.
  • Myosin helps in moving vesicles, organelles and other molecules inside the cell. It also plays a crucial role in muscle contraction and cellular transport.
Based on Where They Are Found
  • Actin is present in all eukaryotic cells, including both muscle and non-muscle cells, where it supports cellular functions.
  • Myosin is mainly found in muscle cells, but some types also exist in non-muscle cells, helping in intracellular transport and cell movement.
Based on Type of Movement
  • Actin mostly provides structural support and does not move actively but it can reorganize itself as needed.
  • Myosin is highly dynamic and moves actively by using ATP, pulling actin filaments for contraction and transport.
Based on Interaction with Other Proteins
  • Actin interacts with tropomyosin, troponin, and actin-binding proteins, which regulate its function.
  • Myosin interacts with myosin light chains and regulatory proteins, which help in its motor activity and ATP usage.






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