Question

Phospholipids are esters of glycerol with

• A. one carboxylic acid residue and two phosphate groups
• B. three phoshate groups
• C. three carboxylic acid residues
• D. two carboxylic acid residues and one phosphate groups

Answer 1

The Correct Option is D

Phospholipids are a class of lipids that are a major component of all cell membranes. They can form lipid bilayers because of their amphiphilic characteristic. The general structure of a phospholipid consists of two parts:

1. Hydrophobic (Water-Repelling) Tails: These tails are typically composed of two fatty acid chains connected to glycerol. Fatty acids are carboxylic acids typically with long chains of hydrocarbons.
2. Hydrophilic (Water-Attracting) Head: This part includes a phosphate group connected to the third carbon of the glycerol backbone.

Based on this structure, phospholipids are esters of glycerol with two carboxylic acid residues and one phosphate group. Therefore, the correct answer is the option: two carboxylic acid residues and one phosphate group.

Let us analyze all the options:

• one carboxylic acid residue and two phosphate groups
  - Incorrect, as phospholipids typically have one phosphate group.
• three phosphate groups
  - Incorrect, not applicable as phospholipids only require one phosphate group and possess two fatty acid tails.
• three carboxylic acid residues
  - Incorrect, because phospholipids have only two carboxylic acid residues.
• two carboxylic acid residues and one phosphate group
  - Correct, corresponding directly with the standard structure of phospholipids described above.

The ability of phospholipids to form bilayers is crucial for constructing the cell membrane and is a key characteristic. This structure allows cells to maintain a stable internal environment.

Extra Tip for Exam Preparation: Understanding the amphiphilic nature of phospholipids helps in grasping their role in biological membranes, especially relevant in biology and biochemistry sections of exams.