Myofibrils and Muscle Fibers

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What remains unaffected by muscle contraction?

Length of the A band

Width of the H zone

Width of the I band

Length of the thick filaments (correct)

What is the composition of the H zone?

Only actin filaments

Actin and myosin filaments

Troponin and tropomyosin

Only myosin filaments (correct)

What happens to troponin when calcium is present?

It covers the actin binding sites

It binds to tropomyosin

It inhibits muscle contraction

It changes shape, releasing tropomyosin (correct)

What is the function of the protein that extends from M lines to Z lines?

Supporting the thin filaments Signup and view all the answers

What is the state of the muscle when there is no calcium present?

Relaxed Signup and view all the answers

What is the sequence of muscle contraction?

Synchronous and asynchronous Signup and view all the answers

What is the approximate percentage of muscle fiber volume occupied by myofibrils?

80% Signup and view all the answers

What is the functional unit of a myofibril, found between Z-lines?

Sarcomere Signup and view all the answers

During muscle growth, what happens to the sarcomeres to increase the length of the muscle fiber?

Sarcomeres are added to the end of myofibrils Signup and view all the answers

What is the role of the subunit of myosin that is responsible for binding actin?

Binding to actin Signup and view all the answers

What is the name of the protein that forms cross bridges with actin?

Myosin Signup and view all the answers

What is the arrangement of thick and thin filaments in a sarcomere?

Each thin filament is surrounded by two thick filaments Signup and view all the answers

What is the function of troponin in muscle contraction?

To hold tropomyosin in place, covering the actin binding sites Signup and view all the answers

What is the role of the ATPase site on the myosin head?

To hydrolyze ATP and provide energy for muscle contraction Signup and view all the answers

What is the function of the I band in muscle structure?

It is the region where the thin filaments are stacked together Signup and view all the answers

What happens to the tropomyosin when calcium is present?

It shifts out of the way, exposing the actin binding sites Signup and view all the answers

What is the function of the myosin heads in muscle contraction?

To form cross bridges with the actin filaments and bring about contraction Signup and view all the answers

What is the structure of the backbone of the thin filaments?

Two strands of actin twisted together Signup and view all the answers