Side by side
| Prokaryotic cell | Eukaryotic cell | |
|---|---|---|
| Nucleus | Absent; the DNA sits in a region of the cytoplasm called the nucleoid | Present, a membrane-bound compartment holding the chromosomes |
| Membrane-bound organelles | None | Present, including mitochondria, endoplasmic reticulum, Golgi and, in plants, chloroplasts |
| Organisms | The predominantly single-celled Bacteria and Archaea | Animals, plants, fungi and protists |
| Typical diameter | 0.1 to 5.0 micrometers | 10 to 100 micrometers |
| Cell wall | Most bacteria have a peptidoglycan wall, and many add a polysaccharide capsule | Present in plants and fungi, where the plant wall's major organic molecule is cellulose; absent in animal cells |
| Surface structures | Some have flagella for locomotion, pili for conjugation, or fimbriae for attaching to a host cell | Varied, including cilia and flagella built on a different internal structure |
| Shared by both | Plasma membrane, cytoplasm, DNA and ribosomes | Plasma membrane, cytoplasm, DNA and ribosomes |
Four things every cell has, and one thing only one type has
The clean way into this comparison is to start from what is universal. All cells share four components: a plasma membrane separating the interior from the environment, cytoplasm containing the other cellular components, DNA as genetic material, and ribosomes to synthesize proteins. Prokaryotes have all four and stop there, because a prokaryote is a simple, mostly single-celled organism that lacks a nucleus or any other membrane-bound organelle, with its DNA held in a region called the nucleoid. Eukaryotes add compartmentalization: a membrane-bound nucleus, plus the organelles that let different chemistries run at different conditions in the same cell.
Where students go wrong
The commonest error is saying prokaryotes have no DNA or no ribosomes because they have no nucleus. They have both; what they lack is the membrane that would wrap the DNA. The second is treating size as incidental. At 0.1 to 5.0 micrometers across, against 10 to 100 for eukaryotic cells, a prokaryote is small enough that ions and organic molecules entering it diffuse quickly to wherever they are needed, and wastes diffuse out just as quickly. Eukaryotic cells cannot rely on that, which is part of why they evolved structural adaptations for intracellular transport.
Where this leads next
Inside the eukaryotes, the next split is between plant and animal cells, which share the entire eukaryotic inventory and differ in a short list of structures, and that is the next page. The nucleus itself is the reason transcription and translation are separated in space in eukaryotes and not in prokaryotes, which is a point the transcription and translation comparison returns to directly. And the organelles that define eukaryotes are where the energy pathways live, since mitochondria host the citric acid cycle and oxidative phosphorylation.
Common mistakes
- Saying prokaryotes have no DNA or no ribosomes. Both are among the four components every cell shares; what is missing is the nuclear membrane.
- Calling all prokaryotes bacteria. The prokaryotes are Bacteria and Archaea, two separate domains.
- Assuming a cell wall makes a cell prokaryotic. Plant and fungal cells have walls too, built from different material.
- Forgetting that eukaryote is not the same as multicellular. Protists are single-celled eukaryotes.
Related concepts
- Plant cell vs animal cell: Both are eukaryotic, so both have a plasma membrane, nucleus, ribosomes, mitochondria and the endomembrane system.
- DNA vs RNA: DNA and RNA are both polynucleotides, but DNA uses deoxyribose and the bases A, T, G and C, and forms an antiparallel double helix.
- Transcription vs translation: Transcription copies a gene's DNA sequence into messenger RNA, one nucleotide at a time.