Question

The translocation of \(\mathrm{Ca}^{2+}\) across a membrane involves all of the following except A. active transport by \(\mathrm{Ca}^{2+}\) -transporting ATPases. B. maintaining \(\left[\mathrm{Ca}^{2+}\right]\) very much higher in the cell than in extracellular fluid. C. phosphorylation of the transporter. D. regulation by the binding of a \(\mathrm{Ca}^{2+}\) -calmodulin complex to the transporter in cukaryotes. Farent different

Short answer

A. Active transport by Ca²⁺-transporting ATPases B. Maintaining higher calcium concentrations inside the cell than in extracellular fluid C. Phosphorylation of the transporter D. Regulation by binding of a calcium-calmodulin complex to the transporter Answer: B. Maintaining higher calcium concentrations inside the cell than in extracellular fluid.

Step-by-step solution

Understand \(\mathrm{Ca}^{2+}\) Transport

Calcium ion transport is a crucial process in maintaining physiological functions such as muscle contraction, nerve impulse transmission, and cell signaling in eukaryotic cells. Let's analyze each statement to determine its relevance to calcium ion transport.

Analyze Option A

Option A states that active transport by \(\mathrm{Ca}^{2+}\)-transporting ATPases is involved in calcium ion transport. This statement is true, as \(\mathrm{Ca}^{2+}\)-transporting ATPases are involved in maintaining the calcium gradient across membranes, and ATPase activity requires energy from ATP hydrolysis. So, this statement is not the answer.

Analyze Option B

Option B states that calcium transport involves maintaining higher calcium concentrations inside the cell than in extracellular fluid. This statement is false, as the correct scenario is the opposite: calcium concentrations are maintained lower inside the cell compared to extracellular fluid; this gradient is essential for proper functioning of cellular calcium signaling. Hence, Option B is the answer since it does not contribute to the transport of calcium ions across membranes.

Analyze Option C

Option C mentions that phosphorylation of the transporter is involved in calcium transport. This statement is true, as during the transport cycle, \(\mathrm{Ca}^{2+}\)-transporting ATPase is phosphorylated and subsequently dephosphorylated, allowing the transport of calcium ions across the membrane. Since this is a true statement, it is not the answer.

Analyze Option D

Option D states that regulation by binding of a calcium-calmodulin complex to the transporter is involved in eukaryotic calcium transport. This statement is true; calcium ions interact with calmodulin to modulate the activity of various protein targets, one of which is the calcium pump. Since this is a true statement, it is not the answer.

Results

After analyzing all options, we conclude that Option B is the correct answer. The transport of \(\mathrm{Ca}^{2+}\) ions does not involve maintaining higher calcium concentrations inside the cell compared to extracellular fluid; in fact, the opposite is true. Therefore, Option B is the statement that doesn't participate in the translocation of \(\mathrm{Ca}^{2+}\) ions across a membrane.