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. This type of transport system A. moves \(\mathrm{Na}^{+}\) and the amino acid or glucose in opposite directions across the membrane. B. uses the energy of the Na' gradient (SMF) to concentrate the other substance against its gradient. C. results in the hydrolysis of ATP during the transport. D. is the same as coded for by the multidrug resistance (Mdr) family of genes. E. is the only type of system used to transport glucose across membranes.

Short answer

Answer: B. The transport system uses the energy of the Na+ gradient (Sodium Motive Force, SMF) to concentrate the other substance against its gradient.

Step-by-step solution

Read and Understand the Exercise

Read the exercise carefully and identify the facts about these transport systems: 1. They are Na+/amino acid or Na+/glucose co-transporters 2. In Hartnup disease, there is a decrease in transport of neutral amino acids by the intestine and renal tubules. 3. Individuals with decreased glucose uptake from the intestinal tract lack a specific glucose-galactose transporter. Now, let's analyze each statement (A, B, C, D, and E).

Analyzing Statement A

Statement A states that the transport system moves Na+ and the amino acid or glucose in opposite directions across the membrane. However, the exercise states it is a Na+/amino acid or Na+/glucose co-transporter, which indicates that both Na+ and the other molecule are transported in the same direction. Therefore, statement A is incorrect.

Analyzing Statement B

Statement B states that the transport system uses the energy of the Na+ gradient (Sodium Motive Force, SMF) to concentrate the other substance against its gradient. By definition, a co-transporter moves two substances across the membrane in the same direction using the energy of one ion's gradient. In this case, the Na+ gradient provides the energy needed to transport the other substance. Thus, statement B correctly describes this transport system.

Analyzing Statement C

Statement C states that the transport system results in the hydrolysis of ATP during the transport. However, co-transporters do not directly use ATP; instead, they use the energy of one ion's gradient (Na+ gradient in this case). Therefore, statement C is incorrect.

Analyzing Statement D

Statement D says that the transport system is the same as coded for by the multidrug resistance (Mdr) family of genes. Mdr genes code for ATP-binding cassette transporters, which are different from co-transporters. Thus, statement D is incorrect.

Analyzing Statement E

Statement E states that this type of transport system is the only type used to transport glucose across membranes. However, there are other types of transporters, such as facilitated diffusion transporters, that also transport glucose across membranes. So, statement E is incorrect.

Conclusion

After analyzing each statement, we can conclude that statement B is the correct answer. This type of transport system (Na+/amino acid or glucose co-transporters) uses the energy of the Na+ gradient (SMF) to concentrate the other substance against its gradient.