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

To determine which molecule would freely diffuse through a kidney cell plasma membrane without transport proteins, we need to consider membrane permeability properties. The lipid bilayer favors nonpolar, hydrophobic, relatively small molecules that can dissolve in the lipid core and cross by simple diffusion.

Option 1: Beta-Carotene. This molecule is highly hydrophobic and nonpolar, characteristic of substances that can move through the lipid bilayer without assistance. While it is relatively large, its lipophilicity makes passive diffusion across the membrane plausible compared to polar or charged species. This makes it a strong candidate for free diffusion.

Option 2: Guanine. Guanine is a polar, nitrogen-containing base with capacity to form hydrogen bonds and carries polar groups. Its polar nature reduces its ability to partition into the hydrophobic core of the membrane, so it would be less likely to diffuse freely without help and would typically require transport mechanisms or channels.

Option 3: Acetoacetate. Acetoacetate is a small organic acid (a carboxylate) that carries a negative charge at physiological pH. Charged species do not readily cross the hydrophobic lipid bilayer without transport or specific channels, so diffusion would be limited and transport proteins or channels are usually needed.

Option 4: Psilocybin. Psilocybin is a large, highly polar molecule with multiple phosphate groups. Its size and charge hinder passive diffusion through the membrane, and it would generally require transport processes or enzymatic modification to cross, not a simple diffusion process.

In summary, the differentiating factor is membrane permeability: nonpolar, hydrophobic molecules diffuse readily, whereas polar or charged molecules do not. Among the options, Beta-Carotene best fits the criterion for free diffusion through the plasma membrane without transport proteins.

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?单项选择题

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