By Drew Lichtenstein | Updated Aug 30, 2022
Over 99% of the elements that compose organic molecules are carbon, hydrogen, and oxygen. These three atoms are the building blocks of carbohydrates, lipids, proteins, and more. When nitrogen joins this trio, it forms the nucleic acids—DNA and RNA—that carry genetic information.
Carbon is the cornerstone of organic chemistry. Its ability to form four covalent bonds—and in some cases up to six—allows it to serve as a versatile hub in countless molecular structures. This flexibility makes carbon the defining element of life and accounts for roughly 10% of the human body’s mass.
Hydrogen is the universe’s most abundant element and a common constituent of organic molecules. Its single valence electron enables it to bond strongly with carbon, providing stability to a wide array of compounds. In the human body, hydrogen constitutes about 63% of the total mass.
Oxygen complements carbon’s versatility by forming multiple bonds, though typically not as a central atom. It is essential for the diverse chemistry that sustains life, including the synthesis of proteins, carbohydrates, and lipids. Oxygen makes up approximately 26% of the human body.
Although nitrogen represents only about 1% of the body, its presence is critical for life. It is a key component of nucleic acids—DNA and RNA—which encode the instructions for cellular function and reproduction.
