Calcium Ions (Ca²⁺)are Present in the Endoplasmic Reticulum at Concentrations

question 27

Multiple Choice

Calcium ions (Ca²⁺) are present in the endoplasmic reticulum at concentrations 1,000 times higher than in the cytosol (the gel-like part of the cell outside organelles) .One protein on the endoplasmic reticulum membrane is devoted to allowing Ca²⁺ to move from the endoplasmic reticulum to the cytosol,and another protein moves Ca²⁺ from the cytosol to the endoplasmic reticulum.These processes are not trivial-Ca²⁺ released into the cytosol allows,for example,for muscle contraction and communication between nerve cells.In this pair of Ca²⁺ transport proteins,you would predict that the protein moving Ca²⁺ from the endoplasmic reticulum to the cytosol ________,and the protein that moves Ca²⁺ from cytosol to the endoplasmic reticulum ________.

• A)transports calcium slowly; transports calcium rapidly
• B)works without ATP; requires ATP
• C)requires ATP; works without ATP
• D)is large; is small
• E)is small; is large

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