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The Big Four Elements

In every cell, four elements dominate the atomic composition: carbon, hydrogen, oxygen, and nitrogen. Together they account for roughly 96 % of the atoms that make up living organisms.

Carbon, with its unique ability to form stable covalent bonds with itself, underpins the diversity of organic molecules—proteins, carbohydrates, lipids, and nucleic acids. Hydrogen, oxygen, and nitrogen complete the building blocks that sustain life.

Other Major Elements

Beyond the core quartet, several elements contribute 3.5 % of the total atomic content. These include phosphorus, sulfur, sodium, chlorine, potassium, calcium, and magnesium.

• Phosphorus links nucleotides into the backbone of DNA and RNA.
• Sulfur bridges disulfide bonds in proteins, stabilizing their three‑dimensional structure.
• Sodium, chlorine, potassium, and calcium are essential for generating electrical signals in neurons.
• Magnesium serves as a cofactor for numerous enzymatic reactions.

Trace Elements: Small but Mighty

Trace elements—though present at only 0.5 % of cellular atoms—are indispensable for life. Key trace metals include iron, iodine, manganese, molybdenum, selenium, silicon, tin, vanadium, boron, chromium, cobalt, copper, and fluorine.

• Iron circulates oxygen in hemoglobin.
• Iodine is a building block of thyroid hormones that regulate metabolism.
• Other trace metals act as cofactors for enzymes, enabling critical biochemical pathways.

The Role of Water

Water, composed of hydrogen and oxygen, is the medium that dissolves and facilitates interactions among biomolecules. While it does not form covalent bonds with proteins or nucleic acids, it is essential for enzyme activity, energy storage, and metabolic flux.