ANIMAL PHYSIOLOGY
CHEMICAL SIGNALS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Acts as a second messenger in the signal transduction pathway
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Is found in low concentrations outside the cell
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Is released from the mitochondria and endoplasmic reticulum when a cell signaling molecule binds to a cell-surface receptor
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Is found in low concentrations in the cytoplasm
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Detailed explanation-1: -The low resting [Ca2+]c and the calcium signal have to be tightly regulated because almost every aspect of cell function is controlled by Ca2+, including secretion, gene expression, muscle contraction and metabolism, and any unregulated [Ca2+] elevations would cause cell injury or cell death (Fig.
Detailed explanation-2: -Calcium Pumps Calcium exists as a gradient across the plasma membrane, with extracellular concentrations being about 10, 000 times higher than intracellular ones.
Detailed explanation-3: -Ca2+ triggers synaptic vesicle exocytosis, thereby releasing the neurotransmitters contained in the vesicles and initiating synaptic transmission. This fundamental mechanism was discovered in pioneering work on the neuromuscular junction by Katz and Miledi (1967).
Detailed explanation-4: -Healthy cells maintain a large concentration gradient between extracellular and intracellular calcium. Normal extracellular concentrations of calcium are in the 1-3 mM range and intracellular concentrations are in the micromolar range, 0.1 to 0.2 µM.