What is the role of calcium in muscle contraction?
Calcium binds to tropomyosin to expose the myosin-binding sites on actin.
Calcium is released from the sarcoplasmic reticulum to initiate the sliding of actin and myosin filaments.
Calcium activates the motor neurons to stimulate muscle contraction.
Calcium is required for the relaxation of muscles after contraction.
The Correct Answer is B
Muscle contraction is a complex process that involves the interaction between actin and myosin filaments in the muscle fibers. The sliding of these filaments is initiated by the release of calcium ions from the sarcoplasmic reticulum, a specialized organelle in muscle cells. The calcium ions bind to the protein troponin, which causes a conformational change in the troponin-tropomyosin complex, exposing the myosin-binding sites on actin. This allows the myosin heads to bind to actin, forming cross-bridges that pull the actin filaments toward the center of the sarcomere, resulting in muscle contraction.
Option a) is incorrect because calcium does not bind to tropomyosin directly, but rather binds to the protein troponin, causing a conformational change in the troponin-tropomyosin complex.
Option c) is incorrect because calcium does not activate motor neurons, but rather is released from the sarcoplasmic reticulum in response to an action potential that travels down the motor neuron to the neuromuscular junction.
Option d) is incorrect because calcium is required for muscle contraction, not relaxation. The relaxation of muscles after contraction is due to the active transport of calcium ions back into the sarcoplasmic reticulum, which allows the troponin-tropomyosin complex to return to its resting conformation, blocking the myosin-binding sites on actin and ending the cross-bridge cycle.
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Related Questions
Correct Answer is B
Explanation
Monosaccharides are simple sugars that cannot be further broken down into simpler sugars while disaccharides are composed of two simple sugars.
Carbohydrates are one of the main types of biomolecules and are composed of monomers called monosaccharides. Monosaccharides are simple sugars that cannot be further broken down into simpler sugars. They are usually composed of 3 to 7 carbon atoms and have a general formula of (CH2O)n, where n is a number between 3 and 7. Examples of monosaccharides include glucose, fructose, and galactose.
When two monosaccharides are joined together by a glycosidic bond, they form a disaccharide. Disaccharides are composed of two simple sugars and can be broken down into their constituent monosaccharides by hydrolysis. Examples of disaccharides include sucrose, lactose, and maltose.
Option a) is incorrect because it describes the composition of a disaccharide, not a monosaccharide.
Option c) is incorrect because both monosaccharides and disaccharides can be found in both plants and animals.
Option d) is incorrect because both monosaccharides and disaccharides can be used for energy storage and
structural purposes, depending on their specific structure and function in the organism.
Correct Answer is D
Explanation
Chemical properties are characteristics of a substance that describe its ability to undergo a chemical change or reaction with another substance. Reactivity with acid is a chemical property because it describes how a substance will react with an acid to produce a new substance. Density, melting point, and boiling point are physical properties that describe how a substance behaves under certain conditions but do not involve a chemical change or reaction.
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