Prokaryotic and eukaryotic cells

Understand the idea

There are two basic cell types. Prokaryotic means ‘before a nucleus’ (bacteria). Eukaryotic means ‘true nucleus’ (plant, animal, and your body cells). Despite the gap in complexity, both types do many of the same jobs with the same kind of DNA and the same genetic code.

Every cell has four shared parts. DNA carries instructions: in a nucleoid if prokaryotic, in a membrane-bound nucleus if eukaryotic. A plasma membrane of phospholipid and protein controls what enters. Cytoplasm is the material inside, with fluid cytosol. Ribosomes build proteins.

Eukaryotic cells are larger (about 5–100 μm) and have linear DNA with histones, several chromosomes, and membrane organelles such as mitochondria and ER. Prokaryotes are smaller (about 0.1–5 μm), with circular DNA, plasmids, a nucleoid that has no membrane, smaller ribosomes, and no true membrane organelles.

What to remember

• All cells: DNA, plasma membrane, cytoplasm, ribosomes.
• Prokaryote: no nucleus, circular DNA, small, unicellular.
• Eukaryote: true nucleus, linear chromosomes, organelles.

Recap

Start with the four shared parts, then add the nucleus test. No nucleus and circular DNA: prokaryote. True nucleus and organelles: eukaryote.