A transporter in the plasma membrane of an animal cell imports both glycine and

Question

A transporter in the plasma membrane of an animal cell imports both glycine and Na+. Extracellular levels of glycine are lower than intracellular levels, and experimental data shows that if intact cells are treated with increasing concentrations of glycine, the rate of glycine import plateaus. Which of the following statements about this transporter is FALSE? O This transport process requires intracellular ATP This transporter performs secondary active transport. This transporters activity would be disrupted by a Na* ionophore. This transporter is a carrier This transporter undergoes a conformational change during the import process O O

Explanation / Answer

False statement is the first one- this transport requires intracellular ATP.

The extracellular glycine levels are lower than the intracellular levels so to transport against the concentration gradient, energy of some sort is required, this enegy is given by transport of sodium ions down its concentration gradient (high to low). Therefore this is a co-transport of ions - symport as both the ions are moving in the same direction. This process is called secondary active transport. There is tight coupling between the transport of the two solutes so that the electrochemical gradient of sodium can be used to transport glycine.

This transport is coupled indirectly to the consumption of ATP. The driving force is a transmembrane ion gradient (here sodium) is maintained by a primary active transport (ATP- driven Na+ pump) - it means that the cell has to maintain its levels of sodium ions low inside the cell at all times as compared to the outside. To do this ATP is used to pump back sodium ions to the outside. The pump sustains the sodium ion gradient continously. Hence the name secondary active transport.

Since the process depends on the gradient of Sodium Ions to transport glycine ions, ionophores will disrupt the concentration gradient of sodium maintained inside and outside the cell. So glycine transport will be hindered.

The membrane protein is a carrier protein - carrier proteins behave like enzymes as they should specificity for the ions, as in this case it is sodium and glycine, they have saturation levels as seen in the experiment performed, the glycine level plateaus off.

As carrier proteins they undergo conformation changes in their structure upon binding to its substrate on one side of the membrane and then releases it on the other side.

The ATP required is not directly associated to the transport of glycine. So statement 1 is false. All other statements are correct.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.