Cell Structure and Function, Explained
A clear walkthrough of the cell — the basic unit of life — covering the major organelles, the difference between prokaryotic and eukaryotic cells, and how structure drives function.
Updated 2026-06-10
The cell: life's basic unit
Every living thing is built from cells. Some organisms are a single cell; you are tens of trillions of them, specialized into tissues and organs. Despite that diversity, cells share a common toolkit of structures — and in biology, structure almost always explains function.
The central divide is between prokaryotic cells (bacteria and archaea — no membrane-bound nucleus) and eukaryotic cells (plants, animals, fungi, protists — a true nucleus and specialized organelles). Understanding that split is the foundation for nearly everything else in cell biology.
The major organelles
Nucleus
Houses DNA and directs protein synthesis — the cell's control center.
Mitochondria
Generate ATP through cellular respiration — the cell's power plants.
Ribosomes
Assemble proteins from amino acids following mRNA instructions.
Endoplasmic reticulum
Rough ER builds proteins; smooth ER synthesizes lipids and detoxifies.
Golgi apparatus
Modifies, packages, and ships proteins to their destinations.
Cell membrane
A selectively permeable bilayer controlling what enters and exits.
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