Actin and Myosin Flashcards
What makes up most of the actin filament?
Around 300-400 G actin (globular) proteins
How are G actins arranged?
They polymerise to form 2 twisted strands
What are the 2 twisted strands referred to as?
F actin (fibrous)
What do nebulin proteins do?
They span the length of the F actins and help direct their assembly. They make sure the F actins extend to the right length
What are the names of the capping proteins found on each end of an F actin, and what is their purpose?
On the medial end of the F actin, there is a tropomodulin cap, and a Cap Z on the lateral end. They prevent the F actins from depolymerising or unraveling.
What is the name of the protein that covers the G actins’ binding site when at rest?
Tropomyosin
What happens when calcium is bound to a troponin molecule?
They move the tropomyosins to expose the binding site
Explain the structure of a myosin molecule
Consist of two heavy chain polypeptides
On one side the heavy chains coil around one another to form a long tail
In the middle the tail functions as a hinge to increase tail’s flexibility
On the other side of the molecule, the heavy chains form two globular heads, each connecting to the tail by a short neck domain
What features does the myosin heads (aka crossbridges) have?
Contains a binding site for actin
A site that functions as ATPase
What does the neck region do?
Acts as lever arms or hinges during contraction that allows the heads to pivot
What is associated with the myosin neck domains?
4 light chain polypeptides (2 for each head), regulate movement of the head
