The most studied organism on Earth. This rod-shaped bacterium lives in your gut, powers biotechnology, and taught us the fundamentals of molecular biology.
Explore the elegant machinery of a prokaryotic cell.
Gram-Negative Bacterium
Description here
Function here
Escherichia coli is a Gram-negative, rod-shaped bacterium that normally lives peacefully in the human intestine. But its real fame comes from the laboratory: virtually everything we know about gene regulation, DNA replication, and recombinant DNA technology was first worked out in E. coli.
E. coli divides every 20 minutes under ideal conditions. A single cell could theoretically produce a mass greater than Earth in about 2 days.
Unlike your cells, E. coli has no nuclear membrane. Its DNA floats freely in the cytoplasm as a compacted "nucleoid." Transcription and translation happen simultaneously—ribosomes start translating mRNA while it's still being made.
No mitochondria, no ER, no Golgi. E. coli does everything at its plasma membrane—energy production, protein export, and sensing the environment. Simplicity is efficiency: fewer parts means faster reproduction.
As a Gram-negative bacterium, E. coli has two membranes separated by the periplasmic space with a thin peptidoglycan layer. This architecture provides intrinsic resistance to many antibiotics and houses the LPS endotoxin.
The single circular chromosome (4.6 Mbp) is supercoiled into the nucleoid. Separately, small circular plasmids carry bonus genes—often for antibiotic resistance. These can be transferred between bacteria, spreading resistance horizontally.
Each flagellum is powered by one of the most remarkable molecular machines in nature—a rotary motor that spins at up to 18,000 RPM. It uses proton motive force (not ATP) and can reverse direction in milliseconds, enabling the run-and-tumble chemotaxis strategy.
E. coli's 70S ribosomes are smaller than eukaryotic 80S ribosomes—a difference exploited by antibiotics like tetracycline and streptomycin. During fast growth, ~50,000 ribosomes occupy most of the cytoplasm, churning out proteins at 15-20 amino acids per second.
"If you could line up all the E. coli in your gut end-to-end, they would stretch around the Earth about 2.5 times. Yet they weigh only about 100 grams—roughly the weight of a small apple."