Which lipid type is defined as glycerol plus three fatty acids?

• A. Triglycerides
• B. Phospholipids
• C. Carotenoids
• D. Steroids

Answer: (A)

The lipid type defined by glycerol plus three fatty acids is triglycerides. This molecule forms when each of the three hydroxyl groups on glycerol is esterified to a fatty acid, creating three ester bonds and yielding a neutral lipid known as a triacylglycerol. Triglycerides are the main energy storage form in many organisms, packed in adipose tissue, and provide a high energy yield per gram while being hydrophobic and largely nonpolar. This distinguishes them from phospholipids, which have two fatty acids plus a phosphate-containing head group and are key components of cell membranes; carotenoids, which are pigment molecules with long conjugated double-bond systems; and steroids, which are built from four fused carbon rings and lack glycerol with three fatty acids.