C'mon, give it a shot. Lipids are our 3rd group of organic compounds. No other elements in lipid molecules. Nada, none, zippo, zilch. Just those 3.
Lipids never do.
The carboxyl group gives a molecule an acidic property. And like before, this is accomplished by removing water molecules. Notice that there is no Nitrogen anywhere, so this is definately not a proteiN reaction. The repeating unit in nucleic acids is called a nucleotide . Well, congratulations for getting through all this stuff.