Which of the following molecules illustrated below is most likely to freely diffuse through the kidney cell plasma membrane without the assistance of transport proteins?

Question

BlackTom AI · Accepted Answer

The question asks which molecule is most likely to freely diffuse through the kidney cell plasma membrane without transport proteins, so we should compare properties that govern passive diffusion across a lipid bilayer.
Option analysis:
- Beta-Carotene: This molecule is highly nonpolar and hydrophobic, consisting of a long conjugated hydrocarbon chain with no ionizable groups. Its nonpolarity allows it to partition easily into the lipid core of the membrane, enabling passive diffusion without transport proteins, albeit it is relatively large. This makes it the best candidate among typical intracellularly membrane-permeable compounds presented here.
- Guanine: Guanine is a nucleobase with several polar functional groups capable of hydrogen bonding. At physiological pH, it is largely polar, and may carry some ionic or charged character depending on protonation state. Such polarity reduces its ability to cross the hydrophobic interior of a phospholipid membrane via simple diffusion, so it is unlikely to freely diffuse without assistance.
- Acetate: Acetate exists as an anion (acetate ion) at physiological pH. As an ion, it is highly hydrophilic and repelled by the hydrophobic core of the lipid bilayer, making passive diffusion across the membrane very unfavorable. It must use transport mechanisms or channels if crossing cellular membranes.
- Psilocybin: Psilocybin contains a phosphate group and other polar functionalities, giving it a significant charge at physiological pH. Its ionic character and polarity impede direct diffusion through the lipid bilayer, so it would require transport proteins or facilitated pathways.
In summary, among typical candidates for simple diffusion, nonpolar, lipid-soluble compounds diffuse readily through the membrane, whereas charged or highly polar species do not. Therefore, Beta-Carotene best fits the criterion of freely diffusing through the membrane without transport proteins, whereas the other options would require assistance or would not readily diffuse.
Note: The provided options list appears incomplete in the prompt, but the reasoning compares the stated candidates to justify why Beta-Carotene is the most plausible choice for free diffusion.

Which of the following molecules illustrated below is most likely to freely diffuse through the kidney cell plasma membrane without the assistance of transport proteins?

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