Among the following, which organic molecule is most abundant in cells?

• A. Proteins
• B. Lipids
• C. Nucleic acids
• D. Carbohydrates

Answer: (A)

The question tests which type of organic biomolecule dominates cellular composition by mass. Proteins are the most abundant in cells because they form the vast majority of the cell’s machinery and structure—enzymes, motor proteins, transporters, receptors, cytoskeletal elements, signaling molecules, and many other functional components. A cell expresses a huge variety of proteins, and each protein is a relatively large polymer made of many amino acids, contributing a lot to the total mass. Nucleic acids are essential and present, but there are far fewer copies of DNA per cell (and RNA, while numerous, generally has less total mass than proteins). Lipids make up membranes and energy stores, but their total mass is smaller than that of proteins. Carbohydrates are important for energy and structure in plants, yet they contribute less to the cell’s overall dry mass in most organisms. So the abundance of proteins outstrips the other classes, making them the most abundant organic molecule in cells.