Core structure
Bacteria are prokaryotes. Their cells are much smaller than eukaryotic cells and have a simpler internal organisation.
- The cytoplasm lacks membrane-bound organelles.
- Prokaryotic ribosomes are 70S, smaller than the 80S ribosomes found in the eukaryotic cytoplasm.
- There is no nucleus.
- The main genetic material is a single circular DNA molecule lying freely in the cytoplasm and not associated with proteins.
- The cell is enclosed by a cell-surface membrane.
- Outside the membrane is a cell wall containing murein, a glycoprotein.
The absence of a nucleus and membrane-bound organelles is therefore a major feature distinguishing prokaryotic cells from eukaryotic cells.
Exam Tip: When describing a prokaryote, do not say that it has no DNA. State that it has no nucleus and that its main DNA molecule is circular and free in the cytoplasm.