Which of the following ions binds to the troponin complex, initiating muscle contraction?
Potassium.
Calcium.
Phosphorus.
Sodium.
The Correct Answer is B
Calcium ions play a crucial role in initiating muscle contraction.
When a muscle cell is stimulated to contract by an action potential, calcium channels open in the sarcoplasmic membrane and release calcium into the sarcoplasm.
Some of this calcium attaches to troponin, which causes it to change shape. This shape change exposes binding sites for myosin on the actin filaments.
Myosin’s binding to actin causes cross-bridge formation, and muscle contraction begins.
The other ions mentioned in the question do not have this specific role in muscle contraction.
Potassium ions are important for maintaining the resting membrane potential of cells, but they do not bind to the troponin complex.
Phosphorus ions are important for energy metabolism but do not bind to the troponin complex.
Sodium ions are important for generating action potentials but do not bind to the troponin complex.
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Related Questions
Correct Answer is D
Explanation
The pleura is a double-layered serous membrane that covers each lung and lines the thoracic cage.
The pleura is a vital part of the respiratory tract.
Its role is to cushion the lung and reduce any friction that may develop between the lung, rib cage, and chest cavity.
Each pleura (there are two) consists of a two-layered membrane that covers each lung.
The layers are separated by a small amount of viscous (thick) lubricant known as pleural fluid.
The pleura is comprised of two distinct layers: the visceral pleura and the parietal pleura.
The visceral pleura is the thin, slippery membrane that covers the surface of the lungs and dips into the areas separating the different lobes of the lungs (called the hilum).
Correct Answer is A
Explanation
Urea is a substance that is excreted by sweat glands in response to the breakdown of proteins and the formation of ammonia.
When proteins are broken down, they produce ammonia, which is a highly toxic compound for the body.
Ammonia is then converted into urea and released out of the body through sweat glands.
Choice B. Sebum is not correct because it is an oily substance secreted by sebaceous glands to lubricate and protect the skin, but it is not related to the breakdown of proteins or the formation of ammonia.
Choice C. Water is not correct because while it is a component of sweat, it is not specifically related to the breakdown of proteins or the formation of ammonia.
Choice D. Lysozymes are not correct because they are enzymes found in tears, saliva and other body fluids that have antibacterial properties, but they are not related to the breakdown of proteins or the formation of ammonia.
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