032-Myosin Structure & Function

Summary

This lesson explores the structure and function of motor proteins, specifically myosin and kinesin. Myosin, depicted in purple, consists of two polypeptide chains with globular heads that bind to actin and ATP, facilitating muscle contraction through a cyclical process of binding, hydrolysis, and power strokes. Each head operates independently, allowing for coordinated movement. The presentation includes a detailed description of the myosin mechanism and its role in muscle fibers, setting the stage for a subsequent discussion on kinesin, emphasizing how its structure informs its biological function.

Takeaways

• 😀 Myosin and kinesin are two important motor proteins with similar basic structures but different biological functions.
• 💪 Myosin consists of two polypeptide chains forming a dimer, with each chain featuring a globular head, a long neck, and a coiled tail.
• 🔗 The myosin head has two binding sites: one for actin and another for ATP, essential for its motor function.
• ⚙️ Myosin uses ATP hydrolysis to release energy, triggering conformational changes that facilitate movement.
• 🏋️ Myosin's role is crucial in muscle contraction, as it interacts with actin filaments to draw muscle fibers together.
• 📏 The myosin tails associate to form thick filaments, with heads projecting outwards to contact actin filaments.
• 🔄 The mechanism of myosin involves multiple steps: ATP binding, hydrolysis, and actin binding/release.
• 🚶‍♂️ The power stroke occurs when myosin binds to actin, pulling the muscle fiber in one direction without remaining bound to ATP or ADP simultaneously.
• 🤝 Each myosin head works independently, allowing coordinated movement akin to reaching out and pulling something.
• 🔍 The next lesson will focus on kinesin, exploring how its structure relates to its function and contrasting it with myosin.

Q & A

What are the two motor proteins discussed in the lesson?

The two motor proteins discussed are myosin and kinesin.

What is the basic structural unit of myosin?

The basic structural unit of myosin is a dimer, consisting of two polypeptide chains.

What are the main components of a myosin molecule?

A myosin molecule consists of a globular head region, a long neck region, and an alpha helical tail.

What is the role of ATP in the function of myosin?

ATP binds to myosin, causing a conformational change that reduces its affinity for actin, allowing myosin to detach from the actin filament.

How do the heads of myosin work in relation to each other?

The heads of myosin work independently of one another, even though they are part of the same dimer.

What is the significance of the coiled coil structure in myosin?

The coiled coil structure formed by the tails of myosin dimers provides stability and structural integrity to the thick filament.

What happens during the power stroke of myosin?

During the power stroke, after the myosin head binds to actin, it releases ADP and inorganic phosphate, which causes the head to pivot and pull the actin filament, resulting in muscle contraction.

What is the relationship between myosin and muscle contraction?

Myosin interacts with actin filaments to contract muscle fibers, drawing them closer together during the muscle contraction cycle.

What are the products of ATP hydrolysis in myosin's mechanism?

The products of ATP hydrolysis in myosin's mechanism are ADP and inorganic phosphate.

How will kinesin be compared to myosin in the next lesson?

In the next lesson, the structure and function of kinesin will be examined, and a comparison will be made with myosin to highlight their differences in biological roles and mechanisms.