Cell wallGives the cell its shape; in bacteria it is built of peptidoglycan.
Plasma membrane (cell membrane)Controls what enters and leaves the cell.
CytoplasmEverything inside the plasma membrane; there are no membrane-bound organelles.
NucleoidWhere the single circular chromosome lies; no nuclear membrane surrounds it.
RibosomesBuild the cell's proteins.
CapsuleA sugar or protein coat outside the wall; it helps some bacteria resist defenses.
FlagellumSpins like a propeller to move the cell.
Outside the wall 2
PilusA longer appendage for attaching; a sex pilus passes DNA to another cell.
FimbriaeShort appendages that stick the cell to surfaces.
Inside the cell 1
PlasmidA small circle of extra DNA, often carrying useful genes.
Cell envelope (gram-negative) 3
Outer membraneA second lipid bilayer outside the peptidoglycan, found in gram-negative bacteria.
Peptidoglycan layerThe mesh that makes up the wall; thin in gram-negative cells.
Periplasmic spaceGel-like space between the outer and plasma membranes.
How this list was compiled: Read 2026-09-26. OpenStax Microbiology, 3.3 Unique Characteristics of Prokaryotic Cells, https://openstax.org/books/microbiology/pages/3-3-unique-characteristics-of-prokaryotic-cells : prokaryotic cells lack a nucleus and have a single circular chromosome in a nucleoid; plasmids; ribosomes; inclusions; the cell envelope; the cell wall's major component is peptidoglycan (murein), found only in bacteria; gram-negative cells have a thin peptidoglycan layer, a gel-like matrix in the periplasmic space between the cell wall and the plasma membrane, and a second lipid bilayer, the outer membrane, outside the peptidoglycan; a capsule is an organized layer outside the cell wall of polysaccharides or proteins, and with slime layers makes up the glycocalyx; fimbriae and pili (pili longer and fewer, aiding attachment; the F or sex pilus transfers DNA); flagella act like propellers, a monotrichous flagellum is single and polar. OpenStax Biology 2e, 4.2 Prokaryotic Cells, https://openstax.org/books/biology-2e/pages/4-2-prokaryotic-cells (plasma membrane, cytoplasm, nucleoid, ribosomes, cell wall, capsule, flagella, pili), used as a check. Licence: own work
The drawing: Drawn for this site by script, 2026-09-26. Own work, nothing traced. Licence: own work
How it works
This bacteria cell diagram shows one rod-shaped bacterium cut open, the classic prokaryotic cell: no nucleus and no membrane-bound organelles. Thirteen parts carry a ring, including three layers in an enlarged slice of a gram-negative wall. The simple set keeps 7.
Read the full guide
A prokaryotic cell, labeled
The DNA is a single circular chromosome lying loose in the nucleoid, with no membrane round it. Small rings of extra DNA, the plasmids, float separately, and ribosomes fill the cytoplasm. Outside the plasma membrane come the cell wall and, in many species, a capsule.
Hairs and a whip
Fimbriae are the many short hairs that stick the cell to surfaces. Pili are longer and fewer; a sex pilus passes DNA from one cell to another. The flagellum spins like a propeller to drive the cell along.
In the inset, read from the top: outer membrane, periplasmic space with the peptidoglycan layer inside it, then the plasma membrane.
Questions and answers
What is the difference between a gram-negative and a gram-positive cell wall?
A gram-negative wall, the one in the inset, has a thin peptidoglycan layer inside a periplasmic space and an outer membrane beyond it. A gram-positive wall has a thick peptidoglycan layer and no outer membrane.
Does a bacterium have a nucleus?
No. Its DNA sits in the nucleoid, a region of the cytoplasm with no membrane round it. Lacking a nucleus is what makes it a prokaryotic cell.
What is a plasmid?
A small ring of DNA separate from the chromosome. Plasmids often carry useful genes, and a cell may hold hundreds of them.