Question

Draw the structural formula of a lecithin containing one molecule each of palmitic acid and linoleic acid.

Short answer

Answer: A lecithin molecule containing palmitic acid and linoleic acid consists of a glycerol backbone, a phosphate head group, choline, palmitic acid, and linoleic acid. The palmitic acid and linoleic acid are attached to the glycerol backbone through ester bonds. The phosphate head group is connected to the glycerol backbone via another ester bond, while choline is bonded to the phosphate group through a phosphoester bond.

Step-by-step solution

Understand Lecithin Structure

Lecithin is a type of phospholipid consisting of a glycerol backbone attached to two fatty acids and a phosphate head group. The phosphate head group often has an additional molecule, such as choline, attached to it.

Examine Palmitic Acid and Linoleic Acid

Palmitic acid is a saturated fatty acid with 16 carbon atoms and a carboxylic acid group at the end. Its structural formula is CH3(CH2)14COOH. Linoleic acid is an unsaturated fatty acid with 18 carbon atoms and two double bonds. It also has a carboxylic acid group at the end. Its structural formula is CH3(CH2)3(CH=CHCH2)2(CH2)6COOH.

Attach Fatty Acids to Glycerol Backbone

To form the lecithin molecule, the carboxylic acid groups of the palmitic acid and linoleic acid will form ester bonds with the hydroxyl groups on the glycerol backbone. The structural formula for glycerol is HOCH2CH(OH)CH2OH. We will attach palmitic acid and linoleic acid to different carbon atoms of the glycerol backbone.

Attach Phosphate Head Group and Choline

Next, we will attach the phosphate head group to the last hydroxyl group of the glycerol backbone. The phosphate group has the structural formula H2PO4-. After forming an ester bond with the glycerol backbone, we will attach the choline molecule to the phosphate group via a phosphoester bond. The structural formula for choline is (CH3)3N+CH2CH2OH.

Draw the Complete Structural Formula

Now that we have attached all the components, we can draw the complete structural formula for a lecithin molecule containing palmitic acid and linoleic acid: CH3(CH2)14-OC(O)CH2-CH(OH)-O-P(O)(OH)-O-CH2CH2-N+(CH3)3|| | ||| ||| CH(OH)-CH2-O-CH3(CH2)3-CH=CH-CH2-CH=CH-(CH2)6CH3 In this structure, the palmitic acid is located at the left side and is connected to the first carbon atom of the glycerol backbone through an ester bond. The linoleic acid is attached to the second carbon atom of the glycerol backbone, also through an ester bond. The phosphate head group is connected to the third carbon atom of the glycerol backbone through another ester bond, and choline is bonded to the phosphate group via a phosphoester bond.