Which type of molecule provides the most energy based on C-C bonds?

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

Answer: (B)

The key idea is that energy from metabolism comes from how reduced the carbon atoms in a molecule are. More reduced carbons mean more C–H (and other high-energy) bonds that release a lot of energy when they are oxidized.

Lipids have long hydrocarbon chains that are highly reduced, with many C–C and C–H bonds and relatively little oxygen. When these fatty chains are oxidized during cellular respiration, a large amount of energy is released per unit of mass, making lipids the most energy-dense option.

Carbohydrates are more oxidized and contain more oxygen in their structure, so they release less energy per gram than lipids. Proteins also provide energy when needed, but their structure includes nitrogen and is more costly to break down for energy; nucleic acids, while essential for information storage, have comparatively little energy available for metabolism.

So, because lipids contain the most reduced carbon bonds and yield the most energy upon oxidation, they provide the most energy based on C–C/C–H bonds.