Myofibrils and Muscle Fibers
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Questions and Answers

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?

<p>Supporting the thin filaments (A)</p> Signup and view all the answers

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

<p>Relaxed (D)</p> Signup and view all the answers

What is the sequence of muscle contraction?

<p>Synchronous and asynchronous (D)</p> Signup and view all the answers

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

<p>80% (B)</p> Signup and view all the answers

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

<p>Sarcomere (B)</p> Signup and view all the answers

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

<p>Sarcomeres are added to the end of myofibrils (B)</p> Signup and view all the answers

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

<p>Binding to actin (A)</p> Signup and view all the answers

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

<p>Myosin (B)</p> Signup and view all the answers

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

<p>Each thin filament is surrounded by two thick filaments (D)</p> Signup and view all the answers

What is the function of troponin in muscle contraction?

<p>To hold tropomyosin in place, covering the actin binding sites (C)</p> Signup and view all the answers

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

<p>To hydrolyze ATP and provide energy for muscle contraction (A)</p> Signup and view all the answers

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

<p>It is the region where the thin filaments are stacked together (A)</p> Signup and view all the answers

What happens to the tropomyosin when calcium is present?

<p>It shifts out of the way, exposing the actin binding sites (B)</p> Signup and view all the answers

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

<p>To form cross bridges with the actin filaments and bring about contraction (A)</p> Signup and view all the answers

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

<p>Two strands of actin twisted together (A)</p> Signup and view all the answers

Flashcards

What stays the same length during muscle contraction?

The thick filaments (made of myosin) stay the same length during muscle contraction.

What is the H zone made of?

The H zone only contains myosin filaments, with no actin present. It's like a space between the actin filaments.

What happens to troponin in the presence of calcium?

When calcium binds to troponin, it changes shape, pulling tropomyosin away from the actin binding sites.

What's the function of the protein connecting the M line to the Z line?

The protein titin is like a spring, connecting the M line to the Z line and supporting the thin filaments. It helps maintain the sarcomere structure.

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

When no calcium is present, tropomyosin blocks the actin binding sites, preventing myosin from binding and causing contraction.

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What are the components of muscle contraction?

Muscle contraction involves both synchronous and asynchronous events. Synchronous refers to the coordinated movement of actin and myosin, while asynchronous refers to the sequence of steps involved, like calcium release and ATP hydrolysis.

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What percentage of a muscle fiber is made up of myofibrils?

Myofibrils make up about 80% of a muscle fiber's volume. This means they are a major component of the muscle structure.

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What is the functional unit of a myofibril?

A sarcomere is the functional unit of a myofibril. It's the space between two Z lines and contains all the proteins involved in contraction.

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How do sarcomeres change during muscle growth?

During muscle growth, new sarcomeres are added at the ends of myofibrils, increasing the length of the muscle fiber.

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What is the function of the myosin subunit that binds to actin?

This subunit is the 'head' of the myosin protein. It contains the actin binding site, allowing myosin to attach to actin during contraction.

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What protein forms cross bridges with actin?

Myosin is the protein that forms cross bridges with actin during muscle contraction, allowing the filaments to slide past each other.

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

The thin filament is surrounded by two thick filaments. This arrangement allows for the sliding filament mechanism of contraction.

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What is the function of troponin?

Troponin plays a crucial role in regulating muscle contraction. It acts as a 'gatekeeper', holding tropomyosin in place, preventing myosin from binding to actin until calcium is present.

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

The ATPase site on the myosin head hydrolyzes ATP, releasing energy that powers the movement and detachment of the myosin head during muscle contraction.

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What is the function of the I band?

The I band is the region of the sarcomere where only thin filaments are found. It's like a 'gap' between the thick filaments.

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What happens to tropomyosin in the presence of calcium?

When calcium is present, it binds to troponin, causing it to change shape and shift tropomyosin away from the actin binding sites. This allows myosin to bind to actin, leading to muscle contraction.

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What is the function of the myosin heads?

Myosin heads are responsible for binding to the actin filaments and bringing about contraction. They act like tiny 'motors' that pull the filaments past each other.

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What is the structure of the thin filament backbone?

The thin filaments are made of two strands of actin twisted together. This structure provides strength and flexibility for the filaments.

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