Prokaryotic Cells
Biology: Cambridge International A Level, topic 1.1.6
Prokaryotic Cells
Prokaryotic cells have some features that are also found in eukaryotic cells. Prokaryotic cells may also contain plasmids, a capsule and one or more flagella.
Prokaryotes vs eukaryotes
- Features common to these types of cells are:
- A plasma membrane.
- Cytoplasm.
- DNA.
- Ribosomes (ribosomes are 70S in prokaryotes).
- So, the main difference in terms of organelles is that prokaryotes do NOT have any membrane-bound organelles (e.g. nucleus, mitochondria, Golgi apparatus etc.).
Features of prokaryotic cells
- Key features of prokaryotic cells are:
- 70S ribosomes.
- Unicellular.
- No membrane-bound organelles.
- Typicall 1-5μm in diameter.
- Peptidoglycan (PPG) cell wall.
- No nucleus.
- Circular DNA.
DNA in prokaryotes
- Prokaryotic DNA is found as a circular molecule in the cytoplasm.
- Some prokaryotes have smaller loops of DNA called plasmids that are not part of the main circular DNA molecule.
- Bacteria can exchange plasmids with other bacteria, sometimes receiving beneficial new genes that the recipient can add to their chromosomal DNA.
- Antibiotic resistance is one trait that often spreads through a bacterial colony through plasmid exchange.
Capsule
- The capsule enables prokaryotic cells to attach to surfaces in its environment.
Flagella, pili and fimbriae
- Some prokaryotes have flagella, pili, or fimbriae:
- Flagella are tail-like and used for locomotion.
- Some prokaryotes have none and others have more than one.
- Pili are used to exchange genetic material during a type of reproduction called conjugation.
- Fimbriae are used by bacteria to attach to a host cell.
Test yourself on Prokaryotic Cells
Which four features do all cells contain?
What enables a prokaryotic cell to attach to surfaces in its environment?