Four shared features
Introductory biology compares prokaryotic and eukaryotic cells using four shared features: a cell membrane, cytoplasm, genetic information, and ribosomes. Those features describe the basic cellular plan across the two groups.
The membrane controls the boundary between the cell and its surroundings. Cytoplasm is the water-rich interior where many reactions occur. Genetic information supplies instructions, while ribosomes use those instructions to assemble proteins.
Where cells begin to differ
Prokaryotic cells keep their genetic material in the cell interior without a membrane-bound nucleus. Eukaryotic cells organize DNA inside a nucleus and use other membrane-bound structures for specialized jobs.
That difference changes how the cell is organized, but it does not erase the shared foundation. The four-feature model is a starting point rather than a claim about every cell at every stage: for example, mature mammalian red blood cells expel their nucleus and clear nearly all organelles, including ribosomes, as they develop.
Remember these ideas
Key ideas
- The basic plan of both prokaryotic and eukaryotic cells includes a cell membrane and cytoplasm.
- In that foundational model, genetic information stores instructions and ribosomes build proteins.
- A nucleus is a eukaryotic feature, not a feature shared by every cell.
- Some highly specialized cells lose one or more basic features as they mature.
Make the reasoning visible
Worked example · classify a ribosome
- 1
A ribosome's job is to build proteins by using genetic instructions.
- 2
Both prokaryotic and eukaryotic cells use ribosomes for that job.
- 3
So ribosomes belong to the introductory four-feature model shared by both cell groups.
- 4
Keep the model's limit in view: a highly specialized cell can lose ribosomes as it matures, as a mature mammalian red blood cell does.
Try the next step
Correct a claim about nuclei
A student says, “Every cell has a nucleus because DNA has to be stored somewhere.” What part of that reasoning should you correct first?
How would you explain the difference between “has DNA” and “has a nucleus” to a classmate?