AP Biology Notes: Biological Molecules

Four Things to Know about Biological Molecules

1. Organic compounds are molecules that contain carbon. All living matter is made up of nitrogen, carbon, hydrogen, oxygen, phosphorus, and sulfur (N’CHOPS).
2. Living systems require free energy and matter from the environment to grow, reproduce, and maintain homeostasis. Organisms survive by coupling chemical reactions that increase entropy with those that decrease entropy.
3. The water molecule’s polar nature leads to surface tension (enabling capillary action) and makes it an effective solvent. It expands rather than contracts when it freezes. These properties make water essential to life on Earth.
4. The four most common types of biological molecules are carbohydrates, lipids, proteins, and nucleic acids. Carbs, proteins, and nucleic acids include polymers composed of simpler monomer subunits, which give the molecules their distinctive properties: monosaccharides make up disaccharides and polysaccharides, amino acids make up monopeptides and polypeptides, and nucleotides make up RNA and DNA. Lipids are not technically polymers, but some of them are composed of smaller molecules: triglycerides (fats and oils) contain glycerol and three fatty acids, while phospholipids contain glycerol, two fatty acids, and a modified phosphate group.