Molecules larger than what molecular weight range require specialized carriers to cross membranes?

Molecules larger than what molecular weight range require specialized carriers to cross membranes?

• A. 600-1000 Da
• B. 100-200 Da
• C. 400-700 Da
• D. 1000-1500 Da

Answer: (A)

Membrane crossing is governed by size and lipophilicity. Small, moderately lipophilic molecules diffuse across the lipid bilayer easily, but as molecular weight climbs into the mid hundreds to around a kilodalton, diffusion becomes inefficient. In this range, cells typically rely on specialized carriers—transport proteins or vesicular uptake—to move the molecule across membranes. Therefore, molecules larger than about 600–1000 Da generally require these carriers to cross membranes. The smaller ranges can still pass by diffusion if they’re sufficiently lipophilic, while very large ranges (near or above 1000–1500 Da) are usually too large for ordinary diffusion and common transport routes unless a specific transporter or uptake mechanism is available.

Membrane crossing is governed by size and lipophilicity. Small, moderately lipophilic molecules diffuse across the lipid bilayer easily, but as molecular weight climbs into the mid hundreds to around a kilodalton, diffusion becomes inefficient. In this range, cells typically rely on specialized carriers—transport proteins or vesicular uptake—to move the molecule across membranes. Therefore, molecules larger than about 600–1000 Da generally require these carriers to cross membranes. The smaller ranges can still pass by diffusion if they’re sufficiently lipophilic, while very large ranges (near or above 1000–1500 Da) are usually too large for ordinary diffusion and common transport routes unless a specific transporter or uptake mechanism is available.