25. Consider the following statements each with one or two...

25. Consider the following statements each with one or two blanks. (i) Repeated activation of the muscles can lead to the accumulation of $\underline{(1)}$ due to anaerobic breakdown of glycogen in them, causing fatigue. (ii) The globular head of meromyosin is an active ATPase enzyme and has binding sites for $(2)$ and active sites for $(3)$. (iii) This central part of thick filament, not overlapped by thin filaments is called the (4) . Which one of the following options correctly fills the concerned blanks? (a) (1) - glucose, (4) - A band (b) $^{5 n}$ (1) - pyruvic acid, (2) - troponin, (3) - myosin (c) (2) - ATP, (3) - actin, (4) $-\mathrm{H}$ zone (d) (1) - lactic acid, (4) $-1$ band

25. Consider the following statements each with one or two blanks.
(i) Repeated activation of the muscles can lead to the accumulation of $\underline{(1)}$ due to anaerobic breakdown of glycogen in them, causing fatigue.
(ii) The globular head of meromyosin is an active ATPase enzyme and has binding sites for $(2)$ and active sites for $(3)$.
(iii) This central part of thick filament, not overlapped by thin filaments is called the (4) . Which one of the following options correctly fills the concerned blanks?
(a) (1) - glucose, (4) - A band
(b) $^{5 n}$ (1) - pyruvic acid, (2) - troponin, (3) - myosin
(c) (2) - ATP, (3) - actin, (4) $-\mathrm{H}$ zone
(d) (1) - lactic acid, (4) $-1$ band

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Key Concepts

Anaerobic Glycolysis

During high-intensity or repeated muscle activity where oxygen supply is limited, glycogen is broken down anaerobically. This process converts glucose into pyruvate, which is then reduced to lactic acid, leading to its accumulation. The buildup of lactic acid contributes to muscle fatigue by altering the pH balance within the muscle fibers.

Myosin Head Function and ATPase Activity

The myosin molecule, particularly its globular head, plays a crucial role in muscle contraction. It exhibits ATPase activity, meaning it can hydrolyze ATP to provide the energy necessary for contraction. Additionally, the myosin head has specific binding sites that allow it to interact with actin filaments, which is essential for the cross-bridge cycling that drives contraction.

Sarcomere Structure

The sarcomere is the basic contractile unit of striated muscle fibers, organized into distinct regions where thick (myosin) and thin (actin) filaments overlap in an orderly pattern. One key region of the sarcomere is the H zone—the central part of the thick filament that is not overlapped by thin filaments. This region is important for understanding the structural changes that occur during muscle contraction.

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