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Chapter 12: Problem 17

When muscles contract, a. sarcomeres increase in length. b. actin breaks down ATP. c. myosin slides past actin. d. the H zone disappears. e. calcium is taken up by the sarcoplasmic reticulum.

Short Answer

Expert verified
The correct options are (c) myosin slides past actin, and (d) the H zone disappears during muscle contraction.

Step by step solution

01

Understand the mechanism of muscle contraction

Muscle contraction occurs due to the sliding filament mechanism, which involves the interaction between myosin, a motor protein and actin, a filament protein. ATP is required as an energy source, and calcium ions play a critical role in initiating the contraction process.
02

Evaluate the statement "sarcomeres increase in length"

Sarcomeres are the basic units of a muscle and consist of actin and myosin filaments. During muscle contraction, sarcomeres shorten, not increase in length. So option (a) is incorrect.
03

Evaluate the statement "actin breaks down ATP"

Actin is the thin filament protein that interacts with myosin during contraction. However, it's the myosin heads that break down ATP to produce energy for muscle contraction. So option (b) is incorrect.
04

Evaluate the statement "myosin slides past actin"

This statement is accurate. Myosin is the motor protein that uses ATP to slide past actin filaments, resulting in muscle contraction. Hence, option (c) is correct.
05

Evaluate the statement "the H zone disappears"

The H zone is the region within a sarcomere where only myosin filaments are present. During muscle contraction, the actin filaments slide towards the center, covering the H zone, making it disappear. So option (d) is correct.
06

Evaluate the statement "calcium is taken up by the sarcoplasmic reticulum"

The sarcoplasmic reticulum is responsible for storing and releasing calcium ions to initiate muscle contraction. During the relaxation of muscles, the sarcoplasmic reticulum takes up the calcium ions, not during contraction. So option (e) is incorrect. Conclusion: Based on the provided information, the correct options are (c) myosin slides past actin, and (d) the H zone disappears.

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Most popular questions from this chapter

Match each function to a muscle of the head and neck in the key. a. trapezius b arhicularis aculi c. masseter Moves head and scapula

The thick filaments of a muscle fiber are made up of a. actin. b. troponin. c. fascia. d. myosin.

As ADP and ? are released from a myosin head, a. actin filaments move toward the H zone. b. myosin cross-bridges pull the thin filaments. c. a sarcomere shortens. d. Only a and care correct. e. All of these are correct.

Nervous stimulation of muscles a. occurs at a neuromuscular junction. b. results in an impulse that travels down the T system. c. causes calcium to be released from expanded regions of the sarcoplasmic reticulum. d. All of these are correct.

Compare fast- and slow-twitch muscle fibers. (pages \(264-66\) )
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