Eukaryotic vs Prokaryotic Cell Structure

The main difference is that eukaryotic cells have a nucleus and membrane-bound organelles, while prokaryotic cells have neither. Animal, plant and fungal cells are eukaryotic; bacterial cells are prokaryotic. An organelle is a cell structure with a particular function. A membrane-bound organelle is enclosed by a membrane, separating its contents from the surrounding cytoplasm.

Where is the DNA?

In a eukaryotic cell, long, linear DNA molecules are associated with proteins and form chromosomes inside the nucleus. Prokaryotic cells have no nucleus: their main DNA molecule is circular and lies free in the cytoplasm. Many prokaryotic cells also contain plasmids, which are smaller circles of DNA. So the difference is not whether a cell has DNA, but how that DNA is arranged and where it is found.

What other structures differ?

Eukaryotic cells can contain membrane-bound organelles, such as mitochondria and the endoplasmic reticulum. Mitochondria are involved in aerobic respiration. Plant cells also have chloroplasts, where photosynthesis occurs. Prokaryotic cells do not have these organelles. Both types of cell have a cell-surface membrane, cytoplasm and ribosomes, but prokaryotic ribosomes are smaller. Ribosomes are the structures where proteins are made.

Prokaryotic cells are generally smaller than eukaryotic cells and have a cell wall containing murein. Some also have a capsule or a flagellum. Not all eukaryotic cells have a cell wall: animal cells do not, while plant cell walls contain cellulose. A plant cell and a bacterial cell may therefore both have a wall, but the material making up the wall differs.

Exam tip

If asked to compare them, state the feature in both cell types. For example: “Eukaryotic DNA is enclosed in a nucleus, whereas prokaryotic DNA is free in the cytoplasm.” Avoid saying prokaryotes have no organelles at all: they have ribosomes, but no membrane-bound organelles.