Elements and Biomolecules in Living Systems

Exam Tip: If you see a question asking which elements make up the bulk of living matter, look for "CHON"—Carbon, Hydrogen, Oxygen, and Nitrogen. They account for over $96%$ of your body mass!

The Architecture of Life: Major Biomolecules

Biological molecules, or biomolecules, are organized based on their specific elemental composition. A helpful way to remember the primary elements involved in all major biomolecules is the mnemonic CHONPS (Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, and Sulfur).

The four major classes of biomolecules are:

1. Carbohydrates: Composed of C, H, and O. They serve as a source of quick energy and provide structural support, such as cellulose in plants.
2. Lipids (Fats): Primarily composed of C, H, and O, though phospholipids also include P. Lipids are used for long-term energy storage and are the primary components of cell membranes.
3. Proteins: Composed of C, H, O, N, and S. Proteins are the "workhorses" of the cell, responsible for building tissues and acting as enzymes that catalyze chemical reactions.
4. Nucleic Acids (DNA/RNA): Composed of C, H, O, N, and P. These molecules are responsible for the storage and transfer of genetic information.

Organic vs. Inorganic Compounds

In biological chemistry, we distinguish between molecules based on the presence of carbon.

• Organic Compounds: These are the majority of molecules in your body. An organic compound is defined as any molecule containing two or more carbon atoms. There is one notable exception: methane ($CH_4$) is considered organic despite having only one carbon atom.
• Inorganic Compounds: These are molecules that contain fewer than two carbon atoms.

Summary Table of Biomolecules