Yes, bacteria are cells. Each bacterium is a single, self-contained cell capable of carrying out all the functions needed to stay alive and reproduce. Unlike human cells or plant cells, though, bacterial cells have a much simpler internal structure. They belong to a category called prokaryotes, meaning they lack a nucleus and the complex internal compartments found in the cells of animals, plants, and fungi.
What Makes a Bacterial Cell Different
The cells you’re probably most familiar with, the ones that make up your body, are eukaryotic cells. They have a clearly defined nucleus that houses DNA behind a double membrane, plus dozens of specialized compartments (organelles) that handle tasks like energy production and waste processing. Bacterial cells skip all of that. Their DNA floats in a concentrated region of the cell called the nucleoid, with no membrane separating it from everything else. They also lack the internal organelles that eukaryotic cells rely on.
This doesn’t mean bacterial cells are featureless blobs. They pack a surprising amount of function into a tiny package. The plasma membrane, the thin layer surrounding the cell’s interior, handles duties that would be split among multiple organelles in a human cell. It runs the cell’s energy systems, manages transport of nutrients in and waste out, and anchors the DNA during cell division. The interior is densely packed with ribosomes, the molecular machines that build proteins, along with granules that store energy reserves.
How Bacterial Cells Are Built
Nearly all bacteria are wrapped in a rigid cell wall sitting outside the plasma membrane. This wall is made of a mesh-like material called peptidoglycan, a polymer of sugar chains cross-linked by short protein fragments. It acts like a protective scaffold, preventing the cell from bursting under its own internal pressure, maintaining the bacterium’s shape, and shielding it from harsh conditions. The only bacteria that lack this wall are mycoplasmas, a small group that have evolved to survive without it.
Inside the cell wall, the bacterial chromosome is remarkably compressed. In E. coli, for example, if the DNA were allowed to spread out as a random coil, it would occupy a volume roughly 10,000 times larger than the cell itself. To fit, the DNA is compacted about 50,000-fold into organized loops anchored to a central scaffold of proteins. This is the nucleoid, visible under a microscope as an irregularly shaped mass occupying roughly the middle third of the cell. Many bacteria also carry small, separate rings of DNA called plasmids, which often hold genes for traits like antibiotic resistance.
How Small Are Bacterial Cells
Most bacterial cells are measured in micrometers, units one-thousandth of a millimeter. The well-studied species like E. coli, Staph aureus, and Bacillus subtilis have cell volumes between about 0.4 and 3 cubic micrometers. To put that in perspective, you could line up roughly 500 typical bacteria across the width of a single millimeter. Some marine bacteria are far smaller still, with volumes around 1% that of E. coli.
On the other end of the spectrum, a species called Thiomargarita magnifica shattered assumptions about how large a single bacterial cell can get. Discovered in a marine environment, individual cells of this species average over 9,000 micrometers long, making them visible to the naked eye, roughly the length of a centimeter. That’s about 50 times larger than any previously known giant bacterium. To pull this off, T. magnifica evolved an unusual trick: it stores its DNA and protein-building machinery inside membrane-bound compartments, something no other known bacterium does at this scale. It also carries over half a million copies of its genome, far more than a typical bacterium’s single copy.
How Bacterial Cells Reproduce
Bacteria reproduce by splitting in two through a process called binary fission. The sequence is tightly controlled. First, the cell copies its entire chromosome. The two copies migrate to opposite ends of the cell. Then a ring of proteins assembles at the cell’s midpoint, pinching the membrane inward like a belt tightening around a balloon. As the cell divides, new cell wall material is built at the division site, and two identical daughter cells separate. Under ideal conditions, some species can complete this entire cycle in as little as 20 minutes, which is why bacterial infections can escalate quickly.
Bacteria cannot reproduce sexually. There is no fusion of egg and sperm, no mixing of two parents’ full genomes in the way animals and plants do. They can, however, swap small segments of DNA with neighboring bacteria through several mechanisms, which is one reason antibiotic resistance spreads so efficiently across bacterial populations.
Bacteria vs. Archaea
Bacteria aren’t the only single-celled prokaryotes. A separate group called archaea shares the same basic blueprint: no nucleus, no membrane-bound organelles, usually a single circular chromosome, and a surrounding cell wall. For decades, scientists lumped them together. But genetic analysis revealed that archaea are as different from bacteria as both are from animals and plants, earning them their own branch on the tree of life. The three domains of life are Bacteria, Archaea, and Eukarya (which includes everything from fungi to humans).
The key differences between bacteria and archaea are chemical rather than structural. Their cell membranes are built from different types of fat molecules, their cell walls use different materials (archaea lack peptidoglycan), and their DNA-copying machinery more closely resembles that of eukaryotes. Both, however, are unambiguously cells, each one a complete living unit that takes in energy, grows, and divides on its own.