Question

Indicate whether the following compounds are likely to cross a membrane by nonmediated or mediated transport: (a) ethanol, (b) glycine, (c)cholesterol, (d) ATP.

Short answer

1. Non-mediated transport
2. Mediated transport
3. Non-mediated transport
4. Mediated transport

Step-by-step solution

Introduction

The concentrations on both sides of the membrane dictate the free energy change when moving a substance across a membrane. In contrast, the membrane potential determines the free energy change when transferring ions.

Some membrane-permeable substances can pass across the cell plasma membrane, but others require a protein-based mediator. The process of simple diffusion is non-mediated transport. The activity of certain carrier protein molecules is what makes mediated transport possible.

In solution (a), Ethanol as non-mediated transport

The solubility of a chemical in the non-polar region of the membrane determines the pace at which it diffuses.Non-polar molecules can easily diffuse through biological membranes by non-mediated transport depending on the concentration gradient across the membrane.

Ethanol’s non-polar end allows it to dissolve freely in non-polar cell membranes. As a result of the non-polar end, ethanol may pass across cellular membranes without being mediated.

In solution (b), Glycine as mediated transport

Glycine is a polar charged molecule. It is transported across the membrane via protein-based transporter molecules, primarily the glycine receptor and glycine reuptake inhibitor. Furthermore, an ATP-dependent transport pathway exists in glycine. Hence, it is included in mediated-active transport.

In solution (c), Cholesterol as non-mediated transport

Non-polar molecules are easily dispersed through biological membranes through non-mediated transport, depending on the concentration gradient across the membrane.

Cholesterol constitutes polar and non-polar components. It is polar near the hydroxyl group, but due to phospholipids, it is non-polar towards the fatty acid sections. Cholesterol is easily permeable across the cell membrane due to the existence of a non-polar component.

In solution (d), ATP as mediated transport

The cell membrane cannot pass ATP since it is a charged polar molecule.As a result, it must penetrate the membrane with the help of a transmembrane protein.

Conclusion

As a result, glycine and ATP are mediated transporters, while cholesterol and ethanol are non-mediated transporters.