Molecule Gallery

This page features all of the molecules from Metabolism: From Food to Fuel. You can use it like a key to see what's what. You'll also find information about why we chose to show some of the molecules the way we did and other interesting details.


Throughout the pages of Metabolism: From Food to Fuel, the three main macromolecules from food (and their breakdown products) are color-coded by type. Carbohydrates are red, proteins are green, and fats are yellow.

Depending on the context, the same molecule may be shown with more or less detail. For example, a glucose molecule can be shown in high detail, with color-coded carbon, oxygen, and hydrogen atoms. Or it can be shown as a similar but less-detailed shape that only hints at the individual carbon atoms.

To make it easier to "follow the carbon" as nutrients are broken down, we sometimes show equivalent carbon atoms in different colors. For instance, carbon dioxide may be shown in red if it came from a sugar, in green if it came from an amino acid, or in yellow if it came from a fatty acid. But regardless of the color, carbon dioxide is always the same molecule. The color just makes it easier to see which type of molecule the carbon dioxide came from.


The major macromolecules and their breakdown products all contain hydrogen atoms (as shown above for glucose), but for the most part we don't show them. We leave them out for the sake of simplicity. While hydrogen is an important atom in metabolism, showing it can make processes harder to understand. We chose to focus on the molecules' carbon skeletons, making it easier to follow their path from food to carbon dioxide.

However, we do show hydrogen atoms during some of the steps of breakdown for energy—in water and as protons and electrons (a hydrogen atom is a proton plus an electron). It's important to remember that these hydrogen atoms come from food macromolecules. As these carbon-based molecules are broken down, or oxidized, hydrogen atoms are stripped away, used to generate ATP, and ultimately transferred to water.

ATP and carrier molecules

We most often show ATP and carrier molecules such as NAD, FAD, and Coenzyme A as simplified grey shapes. The simplified shapes allow us to highlight the roles of these molecules while deemphasizing their large size and high level of complexity.

Even though we don't often show their molecular details, ATP and carrier molecules are made of atoms—carbon, oxygen, hydrogen, nitrogen, phosphorus, and the occasional sulfur—just like the other molecules depicted in Food to Fuel. And their structures are quite interesting. ATP, for instance, is a nucleotide. NAD, FAD, and Coenzyme A are made up of some familiar molecules, including B vitamins, nucleotides, and even an amino acid.

Based on PDB‘s Molecule of the Month, February 2004

APA format:

Genetic Science Learning Center. (2015, September 1) Molecule Gallery. Retrieved December 07, 2018, from

CSE format:


Chicago format:

Genetic Science Learning Center. "Molecule Gallery." Learn.Genetics. September 1, 2015. Accessed December 7, 2018.