What Do Prokaryotic Cells Have

The Actual Components of a Prokaryotic Cell

Prokaryotic cells are the simpler of the two main cell types, lacking a true nucleus and membrane-bound organelles. When you're asking what do prokaryotic cells have, the answer is a specific set of structures that have evolved to keep the cell functioning despite the absence of compartmentalization. I spent years working with bacterial cultures in a lab setting, and the reality is that most people learning this material memorize a checklist and miss how these pieces actually interact under real conditions. The core components are straightforward on paper. Every prokaryotic cell has a plasma membrane made of a phospholipid bilayer. It has cytoplasm, which is the gel-like substance filling the interior. It has ribosomes for protein synthesis, though these are 70S ribosomes rather than the 80S variety found in eukaryotic cells. That difference matters more than textbooks usually indicate, because it's the reason certain antibiotics target bacterial infections without crippling human cells. The genetic material is a single circular chromosome located in a region called the nucleoid. There is no nuclear envelope surrounding it. This is the fundamental distinction from eukaryotic cells. The DNA is supercoiled and associated with some proteins, but nothing resembling histones in the eukaryotic sense. Many prokaryotes also carry plasmids, which are small, circular, extrachromosomal DNA molecules. Plasmids often carry genes for antibiotic resistance or metabolic functions that can be transferred between cells through conjugation.

Structural Features Beyond the Basics

The cell wall is present in most prokaryotes and is a critical structure. Bacterial cell walls are made of peptidoglycan, a polymer of sugars and amino acids. The thickness and layering of peptidoglycan is what distinguishes gram-positive from gram-negative bacteria. Gram-positive cells have a thick peptidoglycan layer with teichoic acids embedded in it. Gram-negative cells have a thin peptidoglycan layer plus an outer membrane containing lipopolysaccharides, which can trigger severe immune responses in animals including humans. Some prokaryotes have a capsule or slime layer outside the cell wall. The capsule is tightly attached and organized. The slime layer is looser and more diffuse. Both contribute to virulence by helping the cell evade phagocytosis. I once worked with a strain of Streptococcus pneumoniae where the capsule expression varied depending on the growth medium, and that variability made vaccine development significantly more complicated than the textbook description suggests. Flagella provide motility. They are long, helical filaments driven by a rotary motor embedded in the cell membrane and cell wall. The motor is powered by proton motive force, not ATP directly. Flagellar arrangement varies: some cells have a single flagellum, others have multiple at one pole, and some are peritrichous with flagella distributed over the entire surface. Pili and fimbriae are shorter, thinner appendages. Fimbriae are primarily for attachment to surfaces and host cells. Pili, particularly the sex pilus, are involved in conjugation and DNA transfer between cells.

Internal Organization Without Organelles

Just because prokaryotes lack membrane-bound organelles doesn't mean they're disorganized. They have protein-based microcompartments called carboxysomes in some autotrophic bacteria, which concentrate Rubisco for more efficient carbon fixation. Magnetosomes are lipid-coated structures containing magnetic iron crystals that help magnetotactic bacteria orient themselves along magnetic fields. Gas vacuoles provide buoyancy control in aquatic bacteria and archaea. The cytoplasm contains inclusions, which are storage granules of materials like polyphosphate, glycogen, or sulfur. These are not membrane-bound but are functionally important. When nutrients are scarce, the cell relies on these reserves. I remember running an experiment where growth phase dramatically affected inclusion content, and cells in stationary phase looked completely different under the microscope compared to log-phase cells, even though they were the same species.

Common Misunderstandings and Practical Pitfalls

One frequent mistake is assuming all prokaryotes have a cell wall. Mycoplasma species lack a cell wall entirely, which makes them naturally resistant to antibiotics that target peptidoglycan synthesis like penicillin. Another is assuming the nucleoid is randomly positioned. In many bacteria, the chromosome is actively organized and positioned within the cell through mechanisms involving nucleoid-associated proteins and the Par system for chromosome segregation. The 70S ribosome distinction is often taught but rarely contextualized. The 70S designation comes from the sedimentation coefficient and reflects the combined size of the 50S large subunit and the 30S small subunit. Antibiotics like tetracycline, chloramphenicol, and erythromycin exploit structural differences between bacterial and eukaryotic ribosomes. But resistance mechanisms are widespread now, and what works in a textbook scenario doesn't always work in clinical practice. I've seen treatment failures where resistance genes on plasmids rendered standard antibiotic protocols ineffective within days. Archaea are prokaryotes too, and their cell walls are fundamentally different from bacterial cell walls. They lack peptidoglycan entirely. Some use pseudopeptidoglycan, others use polysaccharides or protein surface layers. This is why antibiotics targeting peptidoglycan don't affect archaea, and it's a detail that often gets lost in introductory courses that conflate all prokaryotes as simply "bacteria."

What This Means in Practice

If you're studying this material for an exam, the checklist of structures is necessary. If you're actually working with prokaryotic cells in a lab or clinical setting, the interactions between structures matter far more. The cell wall determines gram stain results, which determines initial antibiotic choices. The presence or absence of a capsule affects virulence and vaccine design. Plasmid content can shift rapidly under selection pressure. Flagellar antigens are used in serotyping but can be lost during subculture. None of this is reflected in a simple diagram, but it's what you encounter when the cells stop behaving like textbook examples.