High School Biology : Understanding Sliding Filament Theory

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #768 : High School Biology

In sarcomeres, the thick filament is composed of which protein?

Possible Answers:

Collagen

Titin

Actin

Myosin

Correct answer:

Myosin

Explanation:

Sarcomeres are composed of thick and thin filaments. The thin filament is composed of polymerized actin, while the thick filament is composed of myosin. Titin is a protein that spans the full range of the sarcomere, and is involved in stability and elasticity in the muscle. Collagen is not a primary component of sarcomeres.

Example Question #61 : Organs And Organ Systems

Which statement is incorrect in describing sliding filament theory?

Possible Answers:

The protein complex formed is classically named actomyosin and helps facilitate the "stroke" part of muscle contraction

Actin and myosin filaments stay the same size during contraction

The actin filaments lengthen, while the myosin filaments shorten

The actin and myosin filaments slide past one another

Actin and myosin form a "crossbridge" when myosin binds to actin

Correct answer:

The actin filaments lengthen, while the myosin filaments shorten

Explanation:

The sliding filament theory describes the mechanism that allows muscles to contract. According to this theory, myosin (a motor protein) binds to actin. The myosin then alters its configuration, resulting in a "stroke" that pulls on the actin filament and causes it to slide across the myosin filament. The overall process shortens the sarcomere structure, but does not change the actual length of either filament.

Example Question #2 : Understanding Sliding Filament Theory

In order for muscle contraction to occur, what molecules/ions must be readily available?

Possible Answers:

NADPH and GADPH

Glycogen

GTP and chloride ions

ADP + Pi

Calcium ions and ATP

Correct answer:

Calcium ions and ATP

Explanation:

The correct answer is ATP and calcium ions. Myosin head activation to form a cross-bridge with actin requires ATP, and the cleavage of ATP to ADP + Pi contracts the myosin head and pulls the actin. Calcium is required to expose actin binding sites for myosin in conjunction with troponin. 

Example Question #63 : Organs And Organ Systems

Muscles require a supply of ATP in order to contract. What function is enabled by the release of energy from ATP?

Possible Answers:

Myosin attaching to actin

Shortening of myosin

Myosin bending to pull actin

Myosin detaching from actin

Myosin attaching to the Z-disc

Correct answer:

Myosin detaching from actin

Explanation:

In the sliding filament theory, myosin heads attach to an actin filament, bend to pull the actin filaments closer together, then release, reattach, and pull again. Energy from ATP is required for the myosin head to release from the actin filament—otherwise the myosin heads would remain in the same place, and the muscle would not contract. Even though the filaments are moving, the filaments themselves never actually get shorter or longer.

When ATP stores are depleted, myosin becomes incapable of detaching from actin, and the muscle remains in a taut, flexed state. This is the cause of rigor mortis.

Example Question #5 : Musculoskeletal System

When is ATP required for muscles according to the sliding filament theory?

Possible Answers:

To perform the power stroke, where the myosin heads rotate toward the sarcomere

For the crossbridges to detach from the actin and eventually reorient the myosin heads.

To perform the power stroke, where the myosin heads rotate away from the sarcomere

For crossbridge formation

For the myosin heads to bind the actin

Correct answer:

For the crossbridges to detach from the actin and eventually reorient the myosin heads.

Explanation:

The myosin head will hydrolyze the . Being bound to ADP, this allows the myosin head to form crossbridges by binding to actin. As ADP detaches from the myosin head, the head will produce the power stroke motion, where the myosin heads will rotate toward the sarcomeres. The myosin head will be locked in this position, attached to the actin, until another ATP molecule comes and attaches to the myosin head. This will allow the head to detach from actin and reorient itself to complete the process again. 

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