Question

this diagram compares the relative rates at which various substances cross a cell membrane without any membrane proteins. molecules with lesser permeability coefficients cross the membrane more slowly, meaning that the membrane is less permeable to these molecules.
the chemical structures of indole and tryptophan are very similar. based on chemical structure, why is the membrane less permeable to tryptophan than indole? select all that apply.
indole has fewer polar covalent bonds than tryptophan.
indole has only nonpolar covalent bonds whereas tryptophan has only polar covalent bonds.
tryptophan is a larger molecule than indole.
tryptophan has two full charges whereas indole is neutral.

Explanation:

• Indole has fewer polar covalent bonds than tryptophan: Polar covalent bonds make a molecule more hydrophilic (water - loving). Since the cell membrane is lipid - based (hydrophobic), molecules with more polar covalent bonds (like tryptophan) have a harder time crossing the membrane.
• Tryptophan is a larger molecule than indole: Larger molecules generally have more difficulty diffusing through the lipid bilayer of the cell membrane compared to smaller molecules. As tryptophan is larger, it crosses the membrane more slowly.

Answer:

Indole has fewer polar covalent bonds than tryptophan.
Tryptophan is a larger molecule than indole.