Question

Alterations in membrane transport systems for specific components lead to a number of diseases. In Hartnup discase there is a decrease in transport of neutral amino acids by intestine and renal tubules. Individuals with a decreased glucose uptake from the intestinal tract lack a specific glucosc- galactose transporter. In these diseases the transport systems are \(\mathrm{Na}^{+} /(\text {amino acid })\) or (glucose) \(\mathrm{co}\) -transporters. A different type of transport system that maintains the \(\mathrm{Na}^{*}\) and \(\mathrm{K}^{*}\) gradicnts across the plasma membranc of cells A. involves an enzyme that is an ATPase. B. is a symport system. C. moves \(\mathrm{Na}^{+}\) either into or out of the cell. D. is an electrically neutral system. E. in the membrane hydrolyzes ATP independently of the movement of \(\mathrm{Na}^{+}\) and \(\mathrm{K}^{*}\).

Short answer

Answer: (A) The transport system involves an enzyme that is an ATPase.

Step-by-step solution

Understanding the context

In this problem, we are dealing with the transport systems that play a crucial role in maintaining the Na+ and K+ gradients across the plasma membrane of cells. We are given five different options and need to identify the correct one.

Evaluate option A

Option A states that the transport system involves an enzyme that is an ATPase. The Na+/K+ pump is an example of such a transport system, which is classified as an ATPase enzyme. The Na+/K+ pump moves 3 Na+ ions out of the cell and 2 K+ ions into the cell, using energy from the hydrolysis of ATP. This is a possible correct option.

Evaluate option B

Option B states that the transport system is a symport system. A symport system transports two or more different ions or molecules in the same direction across the membrane. However, the Na+/K+ pump is an example of an antiport system, as it moves Na+ and K+ ions in opposite directions. This option is not correct.

Evaluate option C

Option C states that the transport system moves Na+ either into or out of the cell. The Na+/K+ pump moves Na+ out of the cell, which is true for this transport system. However, it does not indicate the movement of K+ ions, and thus does not provide a complete description of the system. This option is not entirely correct.

Evaluate option D

Option D states that the transport system is electrically neutral. The Na+/K+ pump moves 3 Na+ ions out of the cell and 2 K+ ions into the cell, creating a net movement of one positive charge out of the cell. This transport system is electrogenic and not electrically neutral. This option is not correct.

Evaluate option E

Option E states that the membrane hydrolyzes ATP independently of the movement of Na+ and K+. In the Na+/K+ pump, ATP hydrolysis is coupled to the movement of Na+ and K+ ions across the membrane. The pump directly relies on ATP hydrolysis to move ions against their electrochemical gradients. This option is not correct.

Choose the correct option

Based on the evaluation of each option, Option A correctly describes the transport system that maintains the Na+ and K+ gradients across the plasma membrane of cells. This transport system involves an enzyme that is an ATPase, which is required for the proper functioning of the Na+/K+ pump mechanism. So, the correct answer is (A).