Question

i: Circle one: which one below causes the affinity of the motor protein for the microfilament to dramatically decrease?

1. ADP release
2. ATP binding
3. ATP hydrolysis
4. Pi release

ii: Where in the cell does the motor protein acquire the ATP to do this cellular work ?

Answer 1

The cytoskeleton is a structure that is made up of a network of filaments, which helps to give shape, support, organize cell’s part, and movement of the cell. Microfilaments ( or actin filaments) are one of the three filaments present in the eukaryotic cell structure. They are the narrowest filament made up of actin subunits primarily function in cellular movement.

1. Correct Answer: d. the affinity of the motor protein for the microfilament dramatically decreases after the Pi release.

Explanation

Reason for the correct answer:

Motor proteins are the class of molecular motors that acts as driving force behind the muscle contraction and active transportation of most of the proteins and vesicles in the cytoplasm of the cell. They primarily convert the adenosine triphosphate (ATP-chemical energy) into mechanical energy to promote the motility of the cellular substances in the cell. Myosin (actin motor proteins) is responsible for muscle contraction. Myosin binds to the actin subunits of the actin filaments, hydrolyze ATP for generating force, and move through the actin filament. The movement of myosin through actin filament cause muscle contraction. The binding of motor protein and ATP hydrolysis takes place as follows:

• First, the ATP molecule binds to the motor protein.
• Myosin initiates ATP hydrolysis; conversion of ATP to ADP and Pi molecule.
• Motor protein releases the hydrolyzed ADP and Pi
• Again new molecule of ATP binds to motor protein. This gives the energy to move to next actin subunit, thus, the chemical cycle continues which enables the muscle contraction.

Therefore, the release of phosphate or Pi triggers the myosin power stroke and leads to a conformational change in myosin to revert back to its original conformation. So, the myosin can bind with the new ATP molecule.

Reason for incorrect answers:

1. ADP release: ADP release does not cause the conformational change in the myosin. Thus, it does not decrease the affinity of myosin for the microfilament.
2. .ATP binding: ATP binding to the myosin molecule is the initial step of the chemical cycle that initiates ATP hydrolysis. It does not decrease the affinity of myosin for the microfilament.
3. ATP hydrolysis: ATP hydrolysis converts the ATP to ADP and phosphate molecule. It does not decrease the affinity of myosin for the microfilament.

ii. Correct answer: Motor protein is attached to the microfilament (cytoskeletal structure) when it acquires ATP to do its cellular work of protein transportation and muscle