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Multiple Choice
Which of the following statements about calcium ions in a typical cell is true?
A
In a typical cell, calcium ions are far more abundant in the cytoplasm than in the blood and other extracellular fluid.
B
In a typical cell, calcium ions are rapidly transported into the endoplasmic reticulum in response to G-protein-mediated signals.
C
In a typical cell, calcium ions are not very widely used as second messengers.
D
All of the listed responses are correct.
E
In a typical cell, calcium ions are often concentrated within the endoplasmic reticulum.
Verified step by step guidance
1
Step 1: Understand the role of calcium ions in cellular processes. Calcium ions (Ca²⁺) are crucial for various cellular functions, including muscle contraction, neurotransmitter release, and as second messengers in signal transduction pathways.
Step 2: Examine the distribution of calcium ions within a cell. Calcium ions are typically stored in the endoplasmic reticulum (ER) and mitochondria, rather than being abundant in the cytoplasm. This storage allows cells to regulate calcium levels tightly.
Step 3: Consider the role of calcium ions as second messengers. Calcium ions are widely used as second messengers in cells, particularly in response to signals that activate G-protein-coupled receptors, leading to the release of calcium from the ER.
Step 4: Analyze the statement regarding calcium transport in response to G-protein signals. G-protein-mediated signals often lead to the release of calcium from the ER into the cytoplasm, rather than rapid transport into the ER.
Step 5: Evaluate the statement about calcium concentration in the ER. The endoplasmic reticulum is indeed a major storage site for calcium ions in cells, where they are often concentrated.