Final answer:
The tertiary amine part of the local anesthetic molecule enables it to cross the cell membrane efficiently.
Explanation:
The part of the local anesthetic molecule that allows it to cross the cell membrane is the tertiary amine. Tertiary amines contain a nitrogen atom with three alkyl or aryl groups attached to it. These groups play a crucial role in the lipophilicity of the molecule, enabling it to pass through the cell membrane.
An example of a local anesthetic with a tertiary amine group is procaine, where the tertiary amino group (diethylamino) facilitates membrane penetration.
Additionally, hydrophobic nonpolar carbon chains like those found in quaternary ammonium compounds (quats) aid in infiltrating cell membranes, as seen in the structure of benzylalkonium chloride and cetylpyrimidine chloride.
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