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MCAT

Unit 3: Lesson 1

Chemical and physical sciences practice passage questions

Tension in the muscles

Problem

Human skeletal muscle tissue is uniquely structured by specialized layers. Muscles are composed of a collection of muscle fibers. In turn, these fibers are made of closely packed myofibrils, or a subunit made of tubular muscle cells. These myofibrils are surrounded by sarcoplasm, a substance similar to cytoplasm in other cells. Finally, myofibrils are composed of repeated sections of sarcomeres, which contain actin and myosin filaments.
Physiologists interested in testing muscle cell tension capacity and musculoskeletal dynamics removed a sarcomere from a primate and placed it in physiological laboratory conditions. They analyzed the sarcomere’s movements under a number of different scenarios, including movement. A simplified model of a section of this sarcomere is given in Figure 1.
Figure 1. A section of the sarcomere used by the scientists.
The tension in the actin between each myosin section are summed up and referred to as a single tension. The tension following myosin section 1 (M1) is referred to as TA, and the tension following myosin section 2 (M2) is TB. This section of actin is directly connected to the sarcomere’s end.
Scientists noted that M1 contained an abnormal mass, making its mass greater than the mass of M2. The mass of M1 = 60kDa, and the mass of M2 = 30kDa.
1.6x10start superscript, minus, 24, end superscriptkg = 1kDa. Assume that frictional forces are negligible.
If the mass of M1 > the mass of M2, and the sarcomere is moving with constant velocity, what can be said about the tension in both actin sections?
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