Question

In cell structure and function you learned that calcium ions (Ca2+) are stored in the smooth ER. Some signaling pathways in the cell cause the ER to release the calcium ions into the cytoplasm, which causes the calcium ion concentration in the cytoplasm to increase and at the same time the calcium ion concentration in the ER to decrease. Once the signaling pathway is turned off, the calcium is returned to the ER so that the concentration of calcium in the ER is very high and the concentration in the cytoplasm is almost zero.

• What membrane transport mechanism would you propose is used to return the calcium ions to the ER and why?
• Your answer must include:
  • What type of membrane protein would be used.
  • The location of the membrane protein.
  • A description of how the membrane protein would be used.

Answer 1

1. What membrane transport mechanism would you propose is used to return the calcium ions to the ER?

The membrane transport protein used in return the calcium ions to the ER is Ca²⁺ ATPase.

2. why?

Ca²⁺ ATPase is a pump that uses energy from ATP in the transfer of calcium ions in the lumen of the endoplasmic reticulum during muscle relaxation. it is the most suitable membrane transport. it umps calcium ions back to the ER reducing its level around actin and myosin filaments.

3. location of membrane protein?

this  Ca²⁺ ATPase present on two locations in the cell.

• the membrane of the endoplasmic reticulum - helps in sending calcium ions from outside to lumen of ER.
• on plasma membrane - helps in removing calcium ions from cells to outside.